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How does ISO setting work?

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Anonymous
July 15, 2005 10:08:52 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark
2. Post processes the picture by increasing the brightness, in
software.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.
--
David Arnstein
arnstein+usenet@pobox.com

More about : iso setting work

Anonymous
July 15, 2005 10:08:53 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

David Arnstein wrote:
> The digital cameras that I have seen have a feature that allows the
> user to choose an ISO setting. I would like to know what this feature
> does, since I suspect that it is useless.
>
> My concern is that setting a high ISO number simply
> 1. Causes the camera to take pictures that are quite dark
> 2. Post processes the picture by increasing the brightness, in
> software.
>
> If this is the case, then I prefer to increase the brightness myself,
> in Photoshop.
>
> On the other hand, if the ISO adjustment on the camera actually
> changes the physical properties of the photosensor, then it's a
> different story.
>
> I'd like some feedback on this before I spend my time experimenting
> with different ISO settings.
> --
> David Arnstein
> arnstein+usenet@pobox.com

ISO does not change the physical properties of the photosensor, it
simply brightens the image as you suggest. There is, however, one
crucial difference. It amplifies the signal before digitizing it, and
this keeps down the quantization noise.

-T
Anonymous
July 15, 2005 10:17:39 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

iso settings are to do with how sensitive your sensor is to light , the
higher the iso setting i.e 400-800 1600 means you could take a photo in a
dimmer room than iso 100 or 200.

"David Arnstein" <arnstein@panix.com> wrote in message
news:D b8u3k$l19$1@reader2.panix.com...
> The digital cameras that I have seen have a feature that allows the
> user to choose an ISO setting. I would like to know what this feature
> does, since I suspect that it is useless.
>
> My concern is that setting a high ISO number simply
> 1. Causes the camera to take pictures that are quite dark
> 2. Post processes the picture by increasing the brightness, in
> software.
>
> If this is the case, then I prefer to increase the brightness myself,
> in Photoshop.
>
> On the other hand, if the ISO adjustment on the camera actually
> changes the physical properties of the photosensor, then it's a
> different story.
>
> I'd like some feedback on this before I spend my time experimenting
> with different ISO settings.
> --
> David Arnstein
> arnstein+usenet@pobox.com
Related resources
July 15, 2005 10:17:40 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

Your-Nice wrote:
> iso settings are to do with how sensitive your sensor is to light , the
> higher the iso setting i.e 400-800 1600 means you could take a photo in a
> dimmer room than iso 100 or 200.

Not quite correct. The ISO setting doesn't change the sensor at all. It changes the
amplification in the readout. I

>
> "David Arnstein" <arnstein@panix.com> wrote in message
> news:D b8u3k$l19$1@reader2.panix.com...
>
>>The digital cameras that I have seen have a feature that allows the
>>user to choose an ISO setting. I would like to know what this feature
>>does, since I suspect that it is useless.
>>
>>My concern is that setting a high ISO number simply
>>1. Causes the camera to take pictures that are quite dark

The picture won't come out dark unless oyu use the wrong ISO setting. Most digicams let
you use auutomaic ISO setting as part of a point-and-shoot setting. It works properly
most of the time.

>>2. Post processes the picture by increasing the brightness, in
>> software.

No. it increases the amplification by the camera's electronic hardware.
>>
>>If this is the case, then I prefer to increase the brightness myself,
>>in Photoshop.

You can do that up to a point. If the exposures are really bad, Photoshop or any progam
can't do the job well.

>>
>>On the other hand, if the ISO adjustment on the camera actually
>>changes the physical properties of the photosensor, then it's a
>>different story.
>>
>>I'd like some feedback on this before I spend my time experimenting
>>with different ISO settings.
>>--
>>David Arnstein
>>arnstein+usenet@pobox.com
>

My suggestion to you is to not think of digital photography as a close analog of film
photography. It is more diferent from film than film is from tintype. Each technology
has its own advantages and drawbacks. The more you understand the one you are using, the
better the results you will get.
Anonymous
July 16, 2005 2:40:39 AM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

In message <db8u3k$l19$1@reader2.panix.com>,
arnstein@panix.com (David Arnstein) wrote:

>The digital cameras that I have seen have a feature that allows the
>user to choose an ISO setting. I would like to know what this feature
>does, since I suspect that it is useless.

>My concern is that setting a high ISO number simply
>1. Causes the camera to take pictures that are quite dark

That should not be a problem. If anything, high ISO images should be
brighter if they are different in brightness, either because there is
not enough light for a low ISO image, or the cameras has run out of
shutter speeds or wide aperture to keep the high ISO image from
over-exposing.

>2. Post processes the picture by increasing the brightness, in
> software.

Some cameras achieve their highest ISOs this way, and get the lower
range by varying the gain applied to the sensor capture before it is
turned into numbers. Perhaps some do all of their ISOs this way, but I
don't know how many.

>If this is the case, then I prefer to increase the brightness myself,
>in Photoshop.
>
>On the other hand, if the ISO adjustment on the camera actually
>changes the physical properties of the photosensor, then it's a
>different story.

The normal way does not change the sensor at all; the sensors are fixed
in their sensitivities. The difference between ISOs is usually achieved
by amplifying the signal by different amounts, causing different ranges
of sensor voltages to map to the range of RAW data, usually 0 to 4095.

>I'd like some feedback on this before I spend my time experimenting
>with different ISO settings.

Experimenting will tell you more than other people usually can, and more
than what the manufacturer will tell you.

If the camera has manual exposure, set it up on a tripod or table to
take an image with a full range of tones, and make a normal exposure at
the camera's highest ISO. Now, keep the f-stop and the shutter speed
the same, but set it to the lowest ISO. Boost the exposure level of the
low-ISO image in software to match the high-ISO. If the high-ISO image
has less noise and more detail, then the camera may be using
amplification in hardware, and then you are clearly better off using
high ISO than under-exposing a low ISO image (or having too long a
shutter speed at a low ISO). Even if the camera is using amplification,
if it is JPEG-only, it may be that the camera kills shadow detail when
making a JPEG, to hide noise, in which case you will get poor images if
you boost the exposure, anyway. You can also try the different ISOs
with the same image, and automatic exposure. If the quality
deteriorates rapidly as you go to higher ISOs, then there is probably no
amplification. If the quality is only a little bit worse at each higher
ISO, there is probably amplification. It is also possible that there is
amplifiaction, but it has a lot of noise and distortion.

This is a complex issue, with usually no details coming from the
manufacturer.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 3:31:53 AM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

In article <Xns969511496EC5mvuorikotisoonfi@193.229.0.31>,
Matti Vuori <mvuori@koti.soon.fi> wrote:
>Could you please post in one group only...

I love usenet and I endeavor to be a "good citizen" in this space. I
am very interested in your post.

Would you please explain your reasoning. Here is mine:

1. My post is relevant to all three news groups.
2. By cross-posting, I arrange that an individual using a decent
newsreader will only see my post once, even if he habitually reads
all three news groups.

I look forward to your response Mr. Vuori.
--
David Arnstein
arnstein+usenet@pobox.com
Anonymous
July 16, 2005 3:40:40 AM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

"David Arnstein" <arnstein@panix.com> wrote in message news:D b9h19$ruj$1@reader2.panix.com...
> In article <Xns969511496EC5mvuorikotisoonfi@193.229.0.31>,
> Matti Vuori <mvuori@koti.soon.fi> wrote:
> >Could you please post in one group only...
>
> I love usenet and I endeavor to be a "good citizen" in this space. I
> am very interested in your post.
>
> Would you please explain your reasoning. Here is mine:
>
> 1. My post is relevant to all three news groups.
> 2. By cross-posting, I arrange that an individual using a decent
> newsreader will only see my post once, even if he habitually reads
> all three news groups.
>
> I look forward to your response Mr. Vuori.

I think Matti's post equates to, "I'm not using a decent
news reader and don't know how Usenet works."
Anonymous
July 16, 2005 7:31:28 AM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

David Arnstein wrote:
> The digital cameras that I have seen have a feature that allows the
> user to choose an ISO setting. I would like to know what this feature
> does, since I suspect that it is useless.
>
> My concern is that setting a high ISO number simply
> 1. Causes the camera to take pictures that are quite dark
> 2. Post processes the picture by increasing the brightness, in
> software.
>
> If this is the case, then I prefer to increase the brightness myself,
> in Photoshop.
>
> On the other hand, if the ISO adjustment on the camera actually
> changes the physical properties of the photosensor, then it's a
> different story.
>
> I'd like some feedback on this before I spend my time experimenting
> with different ISO settings.

Vastly oversimplified:
The ISO number is like an amplifier volume setting. The larger the
number the 'louder' the light output from the sensor. And, like a sound
amplifier, excessive settings often produce very distorted, and
'clipped' output. The lower the ISO setting, the more light you need
for a usable picture, but the higher the setting, the more the output
from the sensor is amplified, and the more 'noise', and 'distortion' you
will see. Many cameras use software to improve the image quality, and,
since they have access to the original output from the sensor, they can
usually do this better than Photoshop.


--
Ron Hunter rphunter@charter.net
Anonymous
July 16, 2005 10:33:51 AM

Archived from groups: rec.photo.digital (More info?)

<tsingh@cnds.jhu.edu> wrote:
> David Arnstein wrote:
>>
>> My concern is that setting a high ISO number simply
>> 1. Causes the camera to take pictures that are quite dark
>> 2. Post processes the picture by increasing the brightness, in
>> software.
>>
>> If this is the case, then I prefer to increase the brightness myself,
>> in Photoshop.
>>
>> On the other hand, if the ISO adjustment on the camera actually
>> changes the physical properties of the photosensor, then it's a
>> different story.
>
> ISO does not change the physical properties of the photosensor, it
> simply brightens the image as you suggest. There is, however, one
> crucial difference. It amplifies the signal before digitizing it, and
> this keeps down the quantization noise.

Exactly. Since we only get 12-bit A/D converters (yet) in dSLRs, using an
analog amplifier before the A/D converters should provide better images.

FWIW, here's what's in effect an ISO 100 vs. ISO 3200 comparison (no noise
reduction) in the Canon 300D, where the ISO 3200 is implemented by
underexposing 5 stops at ISO 100 and postprocessing.

Note that using ISO 100 in the 300D for ISO 3200 photography results in
images that are far better than _any_ film could ever dream of.

http://www.pbase.com/davidjl/image/45495842/original

(Note that this does not say that "one should just shoot and ISO 100 and
postprocess", since it doesn't compare in-camera settings and
postprocessing.)

One practical reason to use the ISO settings in the camera is that the noise
reduction in some of the RAW converters is very good. (In particular, I've
been very pleased with Rawshooter essentials.) This saves a step and speeds
up one's work flow a lot.

David J. Littleboy
Tokyo, Japan
Anonymous
July 16, 2005 10:33:52 AM

Archived from groups: rec.photo.digital (More info?)

"David J. Littleboy" <davidjl@gol.com> wrote in message news:D b9a1e$piu$1@nnrp.gol.com...
>
> Exactly. Since we only get 12-bit A/D converters (yet) in dSLRs, using an
> analog amplifier before the A/D converters should provide better images.

David, is that true for all dSLRs? I thought even some high-end
P&S's (e.g. Sony's F717) had 14-bit converters.
Anonymous
July 16, 2005 10:33:52 AM

Archived from groups: rec.photo.digital (More info?)

> http://www.pbase.com/davidjl/image/45495842/original

David, please excuse the huge snip but I'd like you to focus on something.
It's a great demo shot and clearly shows how the S/N ratio is noticeably
better with the 1/4 s exposure as compared to the 1/125 s exposure. But
that's kind of obvious, isn't it?

A third shot with the camera set at ISO 3200 would look about the same as
the 1/125 s exposure ... right? If not, then please explain how
amplification before A/D as opposed to amplification after A/D makes a
significant difference. I am familiar with quantization noise, by the way,
but am looking for something from you that is more practical than
theoretical. I mean to say that your test shots are rather dramatic and
before we get bogged down in technical mumbo jumbo I'd like to see an ISO
3200 equivalent. I am voting for no dramatic difference.

Thanks and, again, it's a great demo shot!
Anonymous
July 16, 2005 10:33:53 AM

Archived from groups: rec.photo.digital (More info?)

In message <HK2dnStRVc6E00XfRVn-2Q@comcast.com>,
"Charles Schuler" <charleschuler@comcast.net> wrote:

>> http://www.pbase.com/davidjl/image/45495842/original
>
>David, please excuse the huge snip but I'd like you to focus on something.
>It's a great demo shot and clearly shows how the S/N ratio is noticeably
>better with the 1/4 s exposure as compared to the 1/125 s exposure. But
>that's kind of obvious, isn't it?
>
>A third shot with the camera set at ISO 3200 would look about the same as
>the 1/125 s exposure ... right?

Not exactly. It could be a small difference, or a tremendous
difference, depending on EC. If the RAW data is digitized so as to
saturate the ~4000 levels in the ISO 100 image, and you use that as a
reference point for the other exposures, the amount of noise is not
tremendous relative to signal, at any ISO, as it would be if the image
were not fully exposed (digitized, actually). I use the term
"digitized" because it is different from film, where absolute exposure
*is* the exposure. With digital, higher ISOs are usually used with
partial sensor exposures, but images come out a lot better even when the
ISO is high, if the RAW levels are fully utilized for that ISO.

The fact is, most "existing light" exposures, especially in situations
that call for high ISO, don't even come close to using the full range of
RAW levels, especially when specular highlights and direct light sources
play into the metering. The average RAW value above blackpoint with
auto-exposure, indoors, with incandescent light on my 20D is something
like 150 to 200 out of 3966 usable levels. Even on that high-exposure
image I posted the other day of the painted letters on the wood blocks,
95% of the pixels were less than 600 RAW levels above blackpoint (almost
3 stops below the clipping point).

>If not, then please explain how
>amplification before A/D as opposed to amplification after A/D makes a
>significant difference. I am familiar with quantization noise, by the way,
>but am looking for something from you that is more practical than
>theoretical.

Quantization noise is not just theoretical; in practice it is clearly
worse than sensor noise, stop for stop. Here's an example (strange
color is due to the fact that the image was not color balanced; this is
the RAW color balance of a black fabric and black plastic buckle).
Technically, the ISO 1600 image was exposed at -2 EC with a grey card,
in manual mose, and only the ISO setting was changed for the ISO 100.
The actual presentation, however, is probably boosted by a stop or a
little more, so what you're seeing appears as EIs 200 and 3200, with a
missing bit each, but the relative effect is still there (rendering them
as black would not make the difference as obvious).

http://www.pbase.com/jps_photo/image/40038800

>I mean to say that your test shots are rather dramatic and
>before we get bogged down in technical mumbo jumbo I'd like to see an ISO
>3200 equivalent. I am voting for no dramatic difference.

There is no gain-based ISO 3200 on the camera, AFAIK.


--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 10:33:53 AM

Archived from groups: rec.photo.digital (More info?)

On Fri, 15 Jul 2005 20:00:21 -0400, Charles Schuler wrote:

> David, please excuse the huge snip but I'd like you to focus on something.
> It's a great demo shot and clearly shows how the S/N ratio is noticeably
> better with the 1/4 s exposure as compared to the 1/125 s exposure. But
> that's kind of obvious, isn't it?
>
> A third shot with the camera set at ISO 3200 would look about the same as
> the 1/125 s exposure ... right? If not, then please explain how
> amplification before A/D as opposed to amplification after A/D makes a
> significant difference. I am familiar with quantization noise, by the way,
> but am looking for something from you that is more practical than
> theoretical.

At the risk of saying something foolish I'll try to answer that.
The two shots should look about the same, because the shutter speeds
(and exposure) were the same for both. The main difference is that
the shot taken using the actual ISO 3200 will have its brightness
boosted by 32x (5 bits worth) by the camera's amplifier. Since (as
David said) the camera uses 12-bit A/D converters, there may
sometimes (but not always) be some isolated highlights that after
32x amplification would exceed the capacity of the 12-bit A/D
converter and cause clipping of the signal, producing blown
highlights. In effect, you're losing the highest 5 bits of picture
information, and now have in effect an image with a smaller, 7-bit
dynamic range.

Since the picture taken with the pseudo ISO 3200 was really shot
at ISO 100, it won't have the 32x amplification boost, and the
12-bits worth of sensor data will be retained and can be sent to the
computer. If the brightness is amplified by a program that doesn't
have the camera's 12-bit limitation, you'll get fewer or no blown
highlights.

On the other hand, if there were no 'bright spots' in the scene,
there would be no highlights to blow and so there shouldn't be a
noticeable difference between the two shots. And then if you decide
that you don't care about any bright highlights (whether they exist
in the scene or not) that would have utilized the top 5 bits of the
A/D converter, you could set the camera to ISO 100. What you'd then
have would be the same image as the one taken at ISO 3200, but with
an additional 5 bits worth of shadow detail, a deal worth its weight
in photons. :) 
Anonymous
July 16, 2005 10:33:54 AM

Archived from groups: rec.photo.digital (More info?)

In message <eppgd1tnhjljg21ag1843j5v0muo9gi0e0@4ax.com>,
ASAAR <caught@22.com> wrote:

>On Fri, 15 Jul 2005 20:00:21 -0400, Charles Schuler wrote:
>
>> David, please excuse the huge snip but I'd like you to focus on something.
>> It's a great demo shot and clearly shows how the S/N ratio is noticeably
>> better with the 1/4 s exposure as compared to the 1/125 s exposure. But
>> that's kind of obvious, isn't it?
>>
>> A third shot with the camera set at ISO 3200 would look about the same as
>> the 1/125 s exposure ... right? If not, then please explain how
>> amplification before A/D as opposed to amplification after A/D makes a
>> significant difference. I am familiar with quantization noise, by the way,
>> but am looking for something from you that is more practical than
>> theoretical.
>
> At the risk of saying something foolish I'll try to answer that.
>The two shots should look about the same, because the shutter speeds
>(and exposure) were the same for both.

That gives equivalent S/N in the analog sensor.

>The main difference is that
>the shot taken using the actual ISO 3200 will have its brightness
>boosted by 32x (5 bits worth) by the camera's amplifier. Since (as
>David said) the camera uses 12-bit A/D converters, there may
>sometimes (but not always) be some isolated highlights that after
>32x amplification would exceed the capacity of the 12-bit A/D
>converter and cause clipping of the signal, producing blown
>highlights.

How is that any different than the the ISO 100 shot? The only
difference is that the ISO 100 shot is more likely to bloom. They will
both clip on the same highlights, with the same relative exposure (EC).

>In effect, you're losing the highest 5 bits of picture
>information, and now have in effect an image with a smaller, 7-bit
>dynamic range.

At the pixel level, yes. At lower spatial frequencies, more levels can
exist via dithering or averaging, albeit noisily.

> Since the picture taken with the pseudo ISO 3200 was really shot
>at ISO 100, it won't have the 32x amplification boost, and the
>12-bits worth of sensor data will be retained and can be sent to the
>computer.

Not at all!

Only 7 bits will be used in any kind of practical way.

>If the brightness is amplified by a program that doesn't
>have the camera's 12-bit limitation, you'll get fewer or no blown
>highlights.

Huh?

> On the other hand, if there were no 'bright spots' in the scene,
>there would be no highlights to blow and so there shouldn't be a
>noticeable difference between the two shots. And then if you decide
>that you don't care about any bright highlights (whether they exist
>in the scene or not)

I understand this stuff very well, but you are confusing the hell out of
me. I can't decide which image you're talking about, a lot of the time.

>that would have utilized the top 5 bits of the
>A/D converter, you could set the camera to ISO 100. What you'd then
>have would be the same image as the one taken at ISO 3200, but with
>an additional 5 bits worth of shadow detail, a deal worth its weight
>in photons. :) 

I don't know which image you're referring to, but both images will clip
at about the same point with default transfer curves in the RAW
conversion, and the image with ISO 3200 set on the camera will have 5
bits less posterization than the image taken at ISO 100 and
under-exposed by 5 stops (4, actually, as ISO 3200 isn't 32x gain; its
16x gain and 2x arithmetic, on most DSLRs).
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 10:33:55 AM

Archived from groups: rec.photo.digital (More info?)

On Sat, 16 Jul 2005 03:15:11 GMT, JPS@no.komm wrote:

> I understand this stuff very well, but you are confusing the hell out of
> me. I can't decide which image you're talking about, a lot of the time.

Funny, but I find your explanations inscrutable at best.
Anonymous
July 16, 2005 10:33:55 AM

Archived from groups: rec.photo.digital (More info?)

On Sat, 16 Jul 2005 03:15:11 GMT, JPS@no.komm wrote:

> I understand this stuff very well, but you are confusing the hell out of
> me. I can't decide which image you're talking about, a lot of the time.

Addendum. Now that I've seen David's latest message, I have to
add that what he says still seems logical and clearly stated, and
still consistent with what I was trying to say, albeit I may not be
speaking the standard jargon that you're used to using. In
contrast, reading your messages often is an adventure, full of
twisty passage, all alike. And based on the various responses in
your reply, it seems like you're jumping to conclusions that I must
be mistaken so you aren't even trying to understand what I've tried
to describe. I think that you understand less than you believe you
do.
Anonymous
July 16, 2005 11:19:57 AM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

David Arnstein wrote:
> In article <Xns969511496EC5mvuorikotisoonfi@193.229.0.31>,
> Matti Vuori <mvuori@koti.soon.fi> wrote:
>> Could you please post in one group only...
>
> I love usenet and I endeavor to be a "good citizen" in this space. I
> am very interested in your post.
>
> Would you please explain your reasoning. Here is mine:
>
> 1. My post is relevant to all three news groups.
> 2. By cross-posting, I arrange that an individual using a decent
> newsreader will only see my post once, even if he habitually reads
> all three news groups.
>
> I look forward to your response Mr. Vuori.

Following that line of reasoning, isn't your post relevant in
rec.photo.digital.zlr as well?

But your reasoning is flawed. If something is of general interest, it
should only be in rec.photo.digital. The aim of splitting the newsgroups
was to reduce the number of postings, and help people focus on their own
interest better. There was no intention to replace the rec.photo.digital
group.

It would be better to restrict your posting to just one group if possible.

Thanks,
David
Anonymous
July 16, 2005 11:54:22 AM

Archived from groups: rec.photo.digital (More info?)

JPS@no.komm wrote:
[]
> Quantization noise is not just theoretical; in practice it is clearly
> worse than sensor noise, stop for stop. Here's an example (strange
> color is due to the fact that the image was not color balanced; this
> is the RAW color balance of a black fabric and black plastic buckle).
> Technically, the ISO 1600 image was exposed at -2 EC with a grey card,
> in manual mose, and only the ISO setting was changed for the ISO 100.
> The actual presentation, however, is probably boosted by a stop or a
> little more, so what you're seeing appears as EIs 200 and 3200, with a
> missing bit each, but the relative effect is still there (rendering
> them as black would not make the difference as obvious).
>
> http://www.pbase.com/jps_photo/image/40038800

Thanks for putting that up, John. Proves your point very nicely (and is a
case where a picture is worth a thousand words!).

So we need more bits in the ADC (and perhaps better shielding in the
pre-ADC circuitry!) if the camera is to capture the full dynamic range of
which that particular sensor is capable?

Cheers,
David
Anonymous
July 16, 2005 1:03:59 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

David Arnstein wrote:
> The digital cameras that I have seen have a feature that allows the
> user to choose an ISO setting. I would like to know what this feature
> does, since I suspect that it is useless.
>
> My concern is that setting a high ISO number simply
> 1. Causes the camera to take pictures that are quite dark
> 2. Post processes the picture by increasing the brightness, in
> software.
>
> If this is the case, then I prefer to increase the brightness myself,
> in Photoshop.
>
> On the other hand, if the ISO adjustment on the camera actually
> changes the physical properties of the photosensor, then it's a
> different story.
>
> I'd like some feedback on this before I spend my time experimenting
> with different ISO settings.

The ISO setting is one parameter the exposure computer uses to determine
exposure (shutter speed and aperture [lens opening]). The default value
should give you the best balanced exposure. There IS now a definition
of the ISO exposure for digital cameras, but I can't find it right now.

You can push a digicam just as you can push a film camera by dialing in
a higher ISO value, which causes a smaller exposure (less energy) than
for the nominal value. This either shortens shutter speed, reduces
aperture, or both, depending on the exposure 'mode' you are using.
Anonymous
July 16, 2005 1:09:13 PM

Archived from groups: rec.photo.digital (More info?)

David J. Littleboy wrote:

>
> Exactly. Since we only get 12-bit A/D converters (yet) in dSLRs, using an
> analog amplifier before the A/D converters should provide better images.
>


All the systems I was familiar with had an amplifier in the signal path
before the A/D, regardless of the ISO setting. A given camera may
change the gain in the amplifier, but here is always an amplifier.

Also, the gain can be changed in effect by programming certain features
of the A/D. I get the impression this is what is done in some cameras
rather than actually using a programmable gain amplifier.

Also, no amount of amplification can change the basic limitation on
dynamic range due to finite well capacity in the CCD wells.
Anonymous
July 16, 2005 1:12:18 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

Andy Sullivan wrote:

>>
>>I look forward to your response Mr. Vuori.
>
>
> I think Matti's post equates to, "I'm not using a decent
> news reader and don't know how Usenet works."
>
>
>

Gee, while I was not the originator of the comment, I guess I myself do
not know how to set up my reader so that it doesn't show up cross posts.
I use Thunderbird. What do I have to do to keep from downloading and
seeing cross posts between rpd and rpe35?
Anonymous
July 16, 2005 1:16:12 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

Ron Hunter wrote:
>
> Vastly oversimplified:
> The ISO number is like an amplifier volume setting. The larger the
> number the 'louder' the light output from the sensor. And, like a sound
> amplifier, excessive settings often produce very distorted, and
> 'clipped' output. The lower the ISO setting, the more light you need
> for a usable picture, but the higher the setting, the more the output
> from the sensor is amplified, and the more 'noise', and 'distortion' you
> will see. Many cameras use software to improve the image quality, and,
> since they have access to the original output from the sensor, they can
> usually do this better than Photoshop.
>
>

I guess I'd argue with this. The sensor (the CCD chip) has the same
output regardless of the amplifier gain. If we push by using a higher
ISO setting, which results in less exposure, there will be fewer
photoelectrons in each well, and the CCD readout signal will be lower.
One can amplify signal AFTER the readout, but the sensor output is lower
when pushing exposure.
Anonymous
July 16, 2005 4:48:13 PM

Archived from groups: rec.photo.digital (More info?)

"Charles Schuler" <charleschuler@comcast.net> wrote:
>> http://www.pbase.com/davidjl/image/45495842/original
>
> David, please excuse the huge snip but I'd like you to focus on something.
> It's a great demo shot and clearly shows how the S/N ratio is noticeably
> better with the 1/4 s exposure as compared to the 1/125 s exposure. But
> that's kind of obvious, isn't it?

Yes. But I think you are missing the point. Have you ever looked at a scan
of ISO 800 film? It's really really gross (incredibly grainy/noisy).

The original complaint here was that since setting the ISO doesn't change
the sensor, digital isn;t as good as film, where you can use any film you
want. I put up that image to point out that dSLR digital at ISO 100 is a
better low-light camera than any film, whatever the ISO.

> A third shot with the camera set at ISO 3200 would look about the same as
> the 1/125 s exposure ... right? If not, then please explain how
> amplification before A/D as opposed to amplification after A/D makes a
> significant difference.

Yes. I realize that I haven't actually spoken to the question at hand. My
point is simply that ISO 100 dSLR digital is a better low-light system than
any 35mm film.

One advantage of shooting correctly exposed ISO 1600 in the camera is that
you can profile the noise characteristics and set up your RAW conversion to
clean up the noise to your liking, even if the noise isn't all that much
lower than underexposed ISO 100.

(I'm currently being amuzed by the noise reduction in RSE. It's a phase,
presumably it will pass. Just a slight touch of RSE noise reduction and ISO
800 images become quite clean.)

> I am familiar with quantization noise, by the way, but am looking for
> something from you that is more practical than theoretical. I mean to say
> that your test shots are rather dramatic and before we get bogged down in
> technical mumbo jumbo I'd like to see an ISO 3200 equivalent. I am voting
> for no dramatic difference.

Well, the 300D only goes to ISO 1600<g>. You are right that I need to do a
4-stop boosted ISO 100 shot vs. and in-camera ISO 1600 shot. My niece is
using my 300D, so that won't happen immediately.

Ah. I see that John Sheehy has already done my homework for me.

http://www.pbase.com/jps_photo/image/40038800/original

Note that John's point here is that were the A/D converter "perfect" (or at
least better than the sensor), then ISO 1600 should look exactly like ISO
100. So your "I am voting for no dramatic difference." would be exactly
right were the A/D converter better.

By the way, there's another subtext going on here. I am of the opinion that
low noise is a very good thing and that sacrificing noise for pixel count is
not something that should be done blithely.

David J. Littleboy
Tokyo, Japan
Anonymous
July 16, 2005 4:48:14 PM

Archived from groups: rec.photo.digital (More info?)

In message <db9vum$veb$2@nnrp.gol.com>,
"David J. Littleboy" <davidjl@gol.com> wrote:

>Yes. I realize that I haven't actually spoken to the question at hand. My
>point is simply that ISO 100 dSLR digital is a better low-light system than
>any 35mm film.

That's with 12-bit digitization; if the current DSLRs had clean 16-bit
digitization, even using current sensor technology, the difference
between film and digital would be big, and totally in favor of digital
(except that some films, especially at larger sizes, have greater
spatial resolution).

Those images I posted recently at ISO 1600 (the paper clip, $20 bill,
wooden alphabet blocks) are what you'd get if you under-exposed ISO 100
by 4 stops! You could set your camera to sunny f/16 at ISO 100, and get
decent shots in deep shade, and excellent shots in the sun. Exposure
latitude would be tremendous.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 4:48:30 PM

Archived from groups: rec.photo.digital (More info?)

In message <O23Ce.70943$G8.2810@text.news.blueyonder.co.uk>,
"David J Taylor"
<david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
wrote:

>So we need more bits in the ADC (and perhaps better shielding in the
>pre-ADC circuitry!) if the camera is to capture the full dynamic range of
>which that particular sensor is capable?

Clearly. Now, the question is, is better digitization available now at
a reasonable price increase, and the companies are being cheap with us,
spoon-feeding technology, or would it be prohibitively expensive to
digitize with a clean 16-bits? The RAW data would only be about 33%
larger, 66% larger in a worst-case scenario (no compression at all of
the extra, relatively noisey 4 bits).

Could be, too, that the companies are using very conservative theory.
Witness the way they stop using analog gain at the highest ISO(s); is
this because they don't think there is any point in digitizing past the
point where a DN represents less than a single electron? Perhaps they
have never explored the benefits of going past that point. The read-out
noise and shot noise are at different scales, so if the DN represents
about one electron, the read-out noise can make the results swing wildly
with posterization. My theory is that you need 3 bits to represent the
individual electron, with a minimum of posterization, and that
digitizing at that level would make the aggregate image; i.e., what you
see when the image is seen in terms of average value in an area, or what
it is actually downsized to, more accurate with less contrasty noise and
posterization, should you choose to make the shadows bright for display
purposes.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 5:32:58 PM

Archived from groups: rec.photo.digital (More info?)

JPS@no.komm wrote:
> In message <O23Ce.70943$G8.2810@text.news.blueyonder.co.uk>,
> "David J Taylor"
> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
> wrote:
>
>> So we need more bits in the ADC (and perhaps better shielding in the
>> pre-ADC circuitry!) if the camera is to capture the full dynamic
>> range of which that particular sensor is capable?
>
> Clearly. Now, the question is, is better digitization available now
> at a reasonable price increase, and the companies are being cheap
> with us, spoon-feeding technology, or would it be prohibitively
> expensive to digitize with a clean 16-bits? The RAW data would only
> be about 33% larger, 66% larger in a worst-case scenario (no
> compression at all of the extra, relatively noisey 4 bits).

I haven't done the sums - what speed of ADC is required? What is an
acceptable power consumption? Here's a 16-bit 100Msample/s ADC:

http://www.analogzone.com/acqp0509.htm

http://www.analog.com/UploadedFiles/Data_Sheets/2645945...

14-bits is also available at a similar and faster speed:

http://www.analog.com/UploadedFiles/Data_Sheets/7717011...

These consume about 2 - 2.5W. What would that do to battery life? Power
management issues internally?

> Could be, too, that the companies are using very conservative theory.
> Witness the way they stop using analog gain at the highest ISO(s); is
> this because they don't think there is any point in digitizing past
> the point where a DN represents less than a single electron? Perhaps
> they have never explored the benefits of going past that point. The
> read-out noise and shot noise are at different scales, so if the DN
> represents about one electron, the read-out noise can make the
> results swing wildly with posterization. My theory is that you need
> 3 bits to represent the individual electron, with a minimum of
> posterization, and that digitizing at that level would make the
> aggregate image; i.e., what you see when the image is seen in terms
> of average value in an area, or what it is actually downsized to,
> more accurate with less contrasty noise and posterization, should you
> choose to make the shadows bright for display purposes.

I suspect that if you went all the way to 16-bits sensor errors and
non-uniformities would become much more apparent than they are right now,
and the electrical design would have to be an order of magnitude better to
avoid electrically coupled noise noises. You'd need to bring in the EMC
experts for the internal design!

Might be more cost-effective to improve the sensor QE a little?

Cheers,
David
Anonymous
July 16, 2005 5:47:37 PM

Archived from groups: rec.photo.digital (More info?)

In message <e08Ce.71131$G8.48347@text.news.blueyonder.co.uk>,
"David J Taylor"
<david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
wrote:

>Might be more cost-effective to improve the sensor QE a little?

That might give better performance at higher ISOs, but it's not going to
give more dynamic range at the lower ISOs, which are currently limited
by digitization, not noise.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 5:50:56 PM

Archived from groups: rec.photo.digital (More info?)

In message <is3id1tobhp4614pfs8q8kgs23dvhrti25@4ax.com>, I,
JPS@no.komm wrote:

>In message <e08Ce.71131$G8.48347@text.news.blueyonder.co.uk>,
>"David J Taylor"
><david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
>wrote:
>
>>Might be more cost-effective to improve the sensor QE a little?
>
>That might give better performance at higher ISOs, but it's not going to
>give more dynamic range at the lower ISOs, which are currently limited
>by digitization, not noise.

.... for DSLRs, that is. For the small-sensor cameras, sensor quality
would result in more usable dynamic range and cleaner images at their
higher ISOs.


--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 6:15:29 PM

Archived from groups: rec.photo.digital (More info?)

JPS@no.komm wrote:
> In message <e08Ce.71131$G8.48347@text.news.blueyonder.co.uk>,
> "David J Taylor"
> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
> wrote:
>
>> Might be more cost-effective to improve the sensor QE a little?
>
> That might give better performance at higher ISOs, but it's not going
> to give more dynamic range at the lower ISOs, which are currently
> limited by digitization, not noise.

Of course. I was thinking "cost-effective" in terms of how you might
improve a digital camera. And as you say, I'm thinking more small-sensor
than DSLR.

Cheers,
David
Anonymous
July 16, 2005 6:49:45 PM

Archived from groups: rec.photo.digital (More info?)

Don Stauffer wrote:
> Ron Hunter wrote:
>>
>> Vastly oversimplified:
>> The ISO number is like an amplifier volume setting. The larger the
>> number the 'louder' the light output from the sensor. And, like a
>> sound amplifier, excessive settings often produce very distorted, and
>> 'clipped' output. The lower the ISO setting, the more light you need
>> for a usable picture, but the higher the setting, the more the output
>> from the sensor is amplified, and the more 'noise', and 'distortion'
>> you will see. Many cameras use software to improve the image
>> quality, and, since they have access to the original output from the
>> sensor, they can usually do this better than Photoshop.
>>
>>
>
> I guess I'd argue with this. The sensor (the CCD chip) has the same
> output regardless of the amplifier gain. If we push by using a higher
> ISO setting, which results in less exposure, there will be fewer
> photoelectrons in each well, and the CCD readout signal will be lower.
> One can amplify signal AFTER the readout, but the sensor output is
> lower when pushing exposure.

Amplifying the signal after readout may show up other imperfections of the
sensor or cross-coupling in the electronics assembly.

The problems with low ISO are reduced sensitivity and hence slower shutter
speeds (image stabilisation can sometimes help here), and the inability of
the sensor to capture more than a certain limiting number of
photo-electrons.

At higher ISOs, with a small photo-electron count, in a well-designed
system the photo-electron noise should predominate. But does it?

Cheers,
David
Anonymous
July 16, 2005 7:07:37 PM

Archived from groups: rec.photo.digital (More info?)

In message <gy8Ce.8$8P.2207@news.uswest.net>,
Don Stauffer <stauffer@usfamily.net> wrote:

>Also, no amount of amplification can change the basic limitation on
>dynamic range due to finite well capacity in the CCD wells.

True, but where is that limit? And does the limit that each sensel have
as an individual measuring device apply to the aggregate image, which
can contain more dynamic range at a lower spatial frequencies?

If one electron registers 1 DN, 2 registers 2 DN, and 3 registers 4 DN,
how could it be a disadvantage to amplify (higher ISO) or digitize
(higher DR) enough that 1 electron registers 9 DN, 2 registers 18, and 3
registers 28 (on average)?
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
July 16, 2005 7:16:05 PM

Archived from groups: rec.photo.digital (More info?)

JPS@no.komm wrote:
> In message <gy8Ce.8$8P.2207@news.uswest.net>,
> Don Stauffer <stauffer@usfamily.net> wrote:
>
>> Also, no amount of amplification can change the basic limitation on
>> dynamic range due to finite well capacity in the CCD wells.
>
> True, but where is that limit? And does the limit that each sensel
> have as an individual measuring device apply to the aggregate image,
> which can contain more dynamic range at a lower spatial frequencies?
>
> If one electron registers 1 DN, 2 registers 2 DN, and 3 registers 4
> DN, how could it be a disadvantage to amplify (higher ISO) or digitize
> (higher DR) enough that 1 electron registers 9 DN, 2 registers 18,
> and 3 registers 28 (on average)?

The normal way to answer that question would be add the RMS value of the
noise sources, so add quantisation noise to the photo-electron noise.
This probably isn't quite mathematically correct for a Poisson
distribution, but I think most people do it just the same.

Often, one noise source predominates, if its RMS value is 2 - 3 times the
value of the other sources, so I guess one should aim for quantisation
noise to be 1/3 of the photon noise. Do that at the dark end and the
light end takes care of itself.....

Is this valid here?

Cheers,
David
Anonymous
July 16, 2005 9:36:28 PM

Archived from groups: rec.photo.digital (More info?)

"David J Taylor"
<david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote:
> David Arnstein wrote:
>
> Following that line of reasoning, isn't your post relevant in
> rec.photo.digital.zlr as well?
>
> But your reasoning is flawed. If something is of general interest, it
> should only be in rec.photo.digital. The aim of splitting the newsgroups
> was to reduce the number of postings, and help people focus on their own
> interest better. There was no intention to replace the rec.photo.digital
> group.
>
> It would be better to restrict your posting to just one group if possible.

Posting to _any_ of the groups under rec.photo.digital makes no sense
whatsoever: their nominal focus is too narrow to have a technical discussion
on any aspect of digital photography.

David J. Littleboy
Tokyo, Japan
Anonymous
July 17, 2005 12:24:23 AM

Archived from groups: rec.photo.digital (More info?)

On Sat, 16 Jul 2005 09:09:13 -0500, Don Stauffer wrote:

> All the systems I was familiar with had an amplifier in the signal path
> before the A/D, regardless of the ISO setting. A given camera may
> change the gain in the amplifier, but here is always an amplifier.

Unless I've missed it, I'm surprised that I haven't seen any
mention of low noise semiconducters and low noise circuits. This is
very important in the design of quality radios that have to dig out
faint signals and make them intelligible. I don't know about the
other companies, but Sony has at least several decades worth of
experience here, and while the A/D's amplifier doesn't have to work
at the high frequencies needed in radios, Sony's experience with low
noise circuits probably can be put to good use in their cameras.
Anonymous
July 17, 2005 1:51:00 AM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

"Don Stauffer" <stauffer@usfamily.net> wrote in message
news:9B8Ce.9$8P.2144@news.uswest.net...
> Andy Sullivan wrote:
>
>>>
>>>I look forward to your response Mr. Vuori.
>>
>>
>> I think Matti's post equates to, "I'm not using a decent
>> news reader and don't know how Usenet works."
>>
>>
>>
>
> Gee, while I was not the originator of the comment, I guess I myself do
> not know how to set up my reader so that it doesn't show up cross posts. I
> use Thunderbird. What do I have to do to keep from downloading and seeing
> cross posts between rpd and rpe35?

Gosh. Here's one instance where Outlook Express manages to meet
expectations. It correctly filters crossposts that are marked as already
read.
Anonymous
July 17, 2005 3:21:43 AM

Archived from groups: rec.photo.digital (More info?)

"Don Stauffer" <stauffer@usfamily.net> wrote:
> David J. Littleboy wrote:
>>
>> Exactly. Since we only get 12-bit A/D converters (yet) in dSLRs, using an
>> analog amplifier before the A/D converters should provide better images.
>
> All the systems I was familiar with had an amplifier in the signal path
> before the A/D, regardless of the ISO setting. A given camera may change
> the gain in the amplifier, but here is always an amplifier.
>
> Also, the gain can be changed in effect by programming certain features of
> the A/D. I get the impression this is what is done in some cameras rather
> than actually using a programmable gain amplifier.

Now that's interesting...

> Also, no amount of amplification can change the basic limitation on
> dynamic range due to finite well capacity in the CCD wells.

And that's a point that we've been ignoring (largely because Roger Clark
hasn't chipped in here yet<g>). The signal from the sensor has a dynamic
range, and more bits than required for that dynamic range would be wasted.
(Which is why Sony's claim of using 14-bit converters in some of their P&S
cameras is probably silly.) JPS's claim that 12 bits is inadequate for the
Canon dSLRs strikes me as probably correct. At least for the 10D/300D, I'd
think.

David J. Littleboy
Tokyo, Japan
Anonymous
July 17, 2005 12:00:47 PM

Archived from groups: rec.photo.digital (More info?)

ASAAR wrote:
> On Sat, 16 Jul 2005 09:09:13 -0500, Don Stauffer wrote:
>
>> All the systems I was familiar with had an amplifier in the signal
>> path before the A/D, regardless of the ISO setting. A given camera
>> may change the gain in the amplifier, but here is always an
>> amplifier.
>
> Unless I've missed it, I'm surprised that I haven't seen any
> mention of low noise semiconducters and low noise circuits. This is
> very important in the design of quality radios that have to dig out
> faint signals and make them intelligible. I don't know about the
> other companies, but Sony has at least several decades worth of
> experience here, and while the A/D's amplifier doesn't have to work
> at the high frequencies needed in radios, Sony's experience with low
> noise circuits probably can be put to good use in their cameras.

That's probably because the signal comes from the sensor chip at an
already-amplified level, so it's the chip design which matters more than
the external electronics (unless that's really badly done). Yes, Sony do
design some of the sensor chips!

David
Anonymous
July 17, 2005 12:00:48 PM

Archived from groups: rec.photo.digital (More info?)

On Sun, 17 Jul 2005 08:00:47 GMT, David J Taylor wrote:

> That's probably because the signal comes from the sensor chip at an
> already-amplified level, so it's the chip design which matters more than
> the external electronics (unless that's really badly done). Yes, Sony do
> design some of the sensor chips!

If by that you mean that the sensors contain their own amplifiers,
then that's where the low noise semiconductors would be needed, not
external to the chip. But based on a recent message remarking on
how sensors under certain operating conditions can get quite warm,
if that's true, then for the lowest noise it probably would be
better for the sensors amplifiers to be located off the chip. In
any case, the more I thought about it the less important low noise
semiconductors would be in cameras, at least compared to their use
in radios. There, if you're trying to listen to a faint signal,
it's important to have a good front end (low noise RF amp) to best
hear weak signals because by definition, the entire signal is very
weak. The same signal picked up by another radio with a poorer RF
amp would present that signal, well, buried in the noise. :)  With
a camera, the low noise circuitry would only provide a significant
benefit to the darkest parts of the picture. Unlike the case with
the radio picking up a weak signal, we might well assume that only a
small percent of the image would have received very little light,
because if the entire image was dark and muddy, in effect the entire
image consisting of shadow detail, then somebody didn't check their
histogram. :) 
Anonymous
July 17, 2005 12:39:15 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

Matti Vuori <mvuori@koti.soon.fi> whined:

>Could you please post in one group only...

If you don't like cross-posting, simply set your kill
filter so you don't see those posts, hypocrite. Your whining
just increasing the damn noise level.
Anonymous
July 17, 2005 1:59:35 PM

Archived from groups: rec.photo.digital (More info?)

ASAAR wrote:
> On Sun, 17 Jul 2005 08:00:47 GMT, David J Taylor wrote:
>
>> That's probably because the signal comes from the sensor chip at an
>> already-amplified level, so it's the chip design which matters more
>> than the external electronics (unless that's really badly done).
>> Yes, Sony do design some of the sensor chips!
>
> If by that you mean that the sensors contain their own amplifiers,
> then that's where the low noise semiconductors would be needed, not
> external to the chip. But based on a recent message remarking on
> how sensors under certain operating conditions can get quite warm,
> if that's true, then for the lowest noise it probably would be
> better for the sensors amplifiers to be located off the chip. In
> any case, the more I thought about it the less important low noise
> semiconductors would be in cameras, at least compared to their use
> in radios. There, if you're trying to listen to a faint signal,
> it's important to have a good front end (low noise RF amp) to best
> hear weak signals because by definition, the entire signal is very
> weak. The same signal picked up by another radio with a poorer RF
> amp would present that signal, well, buried in the noise. :)  With
> a camera, the low noise circuitry would only provide a significant
> benefit to the darkest parts of the picture. Unlike the case with
> the radio picking up a weak signal, we might well assume that only a
> small percent of the image would have received very little light,
> because if the entire image was dark and muddy, in effect the entire
> image consisting of shadow detail, then somebody didn't check their
> histogram. :) 

Your radio receiver analogy isn't a perfect one, because today the major
problem with radio receivers is in preventing multiple off-frequency
signals from interfering with the one you're trying to hear.
Intermodulation performance is more important than absolute sensitivity on
may occasions. What you say is perhaps true in radio astronomy or
satellite reception - although even with geostationary satellites the
close spacing along the Clarke belt can mean that antenna size (and hence
narrow beamwidth) is more important!

You are right about the shadows being important. (I was going to mention
lens flare earlier on in this thread but decided it would only complicate
things...).

My guess, though, is that a reasonable on-chip amplifier would be more
useful than an excellent off-chip amplifier, because of all the transfers
which are required to get the signals from all the detectors off-chip, but
I'm not a chip designer. An interesting point about temperature. Does it
matter for the sorts of durations you might get with hand-held exposures
or just tripod-mounted times? Where is Roger when you need him?

Cheers,
David
Anonymous
July 17, 2005 1:59:36 PM

Archived from groups: rec.photo.digital (More info?)

On Sun, 17 Jul 2005 09:59:35 GMT, David J Taylor wrote:

> Your radio receiver analogy isn't a perfect one, because today the major
> problem with radio receivers is in preventing multiple off-frequency
> signals from interfering with the one you're trying to hear.
> Intermodulation performance is more important than absolute sensitivity on
> may occasions. What you say is perhaps true in radio astronomy or
> satellite reception - although even with geostationary satellites the
> close spacing along the Clarke belt can mean that antenna size (and hence
> narrow beamwidth) is more important!

Well, I was thinking of short wave radio designs, where some of
the better radio's prices begin in the thousands of dollars, and
their low noise characteristics are one of many important spec's.
For regular commercial radios, you're right about the need for good
IM performance. I live within walking distance of a moderately
powerful FM station, and it causes reception problems for most
radios trying to tune in about 10 of the stations nearest to it in
frequency. A few of my better radios have no problem at all. I
suspect, but can't verify that its strong signal also hinders the
reception (using poorly designed radios) of weak AM stations due to
desensitization in the RF section.


> My guess, though, is that a reasonable on-chip amplifier would be more
> useful than an excellent off-chip amplifier, because of all the transfers
> which are required to get the signals from all the detectors off-chip, but
> I'm not a chip designer.

I'm not a chip designer either nor do I play one on TV. But I did
visit a chip fab in Pennsylvania once. MOS Technology, IIRC. But
wouldn't the sensor's data bus width be the same whether the signals
were amplified on the chip or off it? If that's not what you were
referring to then I guess I missed your point.


> An interesting point about temperature. Does it matter for the
> sorts of durations you might get with hand-held exposures
> or just tripod-mounted times?

I don't think the shutter duration matters. Wouldn't the
amplifiers be used only for a short period immediately after the
shutter closes, when the sensor is no longer accumulating photons?


> Where is Roger when you need him?

Relaxing in an Ilya free environment, where if he's reading any
messages at all, they don't end with "Hope this helps". :) 
Anonymous
July 17, 2005 5:53:27 PM

Archived from groups: rec.photo.digital (More info?)

ASAAR wrote:
> On Sun, 17 Jul 2005 09:59:35 GMT, David J Taylor wrote:
[]
>> My guess, though, is that a reasonable on-chip amplifier would be
>> more useful than an excellent off-chip amplifier, because of all the
>> transfers which are required to get the signals from all the
>> detectors off-chip, but I'm not a chip designer.
>
> I'm not a chip designer either nor do I play one on TV. But I did
> visit a chip fab in Pennsylvania once. MOS Technology, IIRC. But
> wouldn't the sensor's data bus width be the same whether the signals
> were amplified on the chip or off it? If that's not what you were
> referring to then I guess I missed your point.

There are a number of techniques for getting the signals from the 6
million (or whatever) sensor sites to the single output pin, which is
analog rather than digital by the way. There are many on-chip transfers
of an analog signal, and I was talking about those data transfers, each of
which could introduce noise and imperfections. Hence the importance of
getting the signal large enough to survive all those transfers without
excessive degradation.

>> An interesting point about temperature. Does it matter for the
>> sorts of durations you might get with hand-held exposures
>> or just tripod-mounted times?
>
> I don't think the shutter duration matters. Wouldn't the
> amplifiers be used only for a short period immediately after the
> shutter closes, when the sensor is no longer accumulating photons?

You're right, of course! I was thinking dark current, but that affects
the capture of the photo-electronis, not the readout.

>> Where is Roger when you need him?
>
> Relaxing in an Ilya free environment, where if he's reading any
> messages at all, they don't end with "Hope this helps". :) 

<G>

David
Anonymous
July 17, 2005 7:33:42 PM

Archived from groups: rec.photo.digital.point+shoot,rec.photo.digital.rangefinder,rec.photo.digital (More info?)

On Sat, 16 Jul 2005 09:12:18 -0500, Don Stauffer wrote:

> Andy Sullivan wrote:
>
>>>
>>>I look forward to your response Mr. Vuori.
>>
>>
>> I think Matti's post equates to, "I'm not using a decent
>> news reader and don't know how Usenet works."
>>
>>
>>
>
> Gee, while I was not the originator of the comment, I guess I myself do
> not know how to set up my reader so that it doesn't show up cross posts.
> I use Thunderbird. What do I have to do to keep from downloading and
> seeing cross posts between rpd and rpe35?
Use Pan instead?
--
neil
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