Sign in with
Sign up | Sign in
Your question

10D overexposure and adjust in PS raw-image converter?

Last response: in Digital Camera
Share
Anonymous
May 8, 2005 8:18:34 AM

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

Bruce Fraser's white paper at

http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf

makes the case that half the information in a digital capture is in
the fifth, or highest, stop. And some digital cameras can capture and
image that is overexposed, thereby driving image information into that
often little-used last stop. The highlights, apparently blown out, can
be recovered in Photoshop's raw image converter.

Using a Canon EOS 10D, I've tried this with some amazingly good
results and some poor results. I'd like to hear about your 10D
experience in this area.

--David
May 8, 2005 4:50:13 PM

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

"David Ellis" <nospam@everywhere.com> wrote in message
news:lo4r711o2nk5pfs3okkhvkro4cj45lclaq@4ax.com...
> Bruce Fraser's white paper at
>
> http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf
>
> makes the case that half the information in a digital capture is in
> the fifth, or highest, stop. And some digital cameras can capture and
> image that is overexposed, thereby driving image information into that
> often little-used last stop. The highlights, apparently blown out, can
> be recovered in Photoshop's raw image converter.
>
> Using a Canon EOS 10D, I've tried this with some amazingly good
> results and some poor results. I'd like to hear about your 10D
> experience in this area.
>
> --David

I quite often adjust the gamma of the photos, from 10D or other cameras,
usually between 1.2 and 1.5 in PSP. Can really bring out the detail but not
sure about the accuracy of the result compared to the original.
Anonymous
May 9, 2005 4:06:48 PM

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

David Ellis wrote:
> Bruce Fraser's white paper at
>
> http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf
>
> makes the case that half the information in a digital capture is in
> the fifth, or highest, stop. And some digital cameras can capture and
> image that is overexposed, thereby driving image information into
that
> often little-used last stop. The highlights, apparently blown out,
can
> be recovered in Photoshop's raw image converter.

I've always wondered how this could be possible. 12 bits of
information, if highlights are blown out then surely that means the
level is at 4095 and can go no higher. How could you possibly 'recover'
extra information from this?

However ... after seeing this I finally understand why:

"... so cameras show the histogram of the image after processing using
the camera's default settings. Most cameras apply a fairly strong
S-curve to the raw data so that the JPEGs have a more film-like
response, with the result that the on-camera histogram often tells you
that your highlights are blown when, in fact, they aren't."

I'm a little miffed that my very expensive camera cannot accurately
inform me of truly blown highlights.
Anonymous
May 9, 2005 5:30:16 PM

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

>The highlights, apparently blown out, can
>be recovered in Photoshop's raw image converter.

If only one channel is clipped then any RAW converter can salvage some
data and reconstruct something. If two channels are clipped they can
still salvage a little bit but with more guesswork and less accuracy.

If all three channels are clipped then there's nothing any RAW
converter can do about it.
Anonymous
May 9, 2005 9:20:51 PM

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

>David Ellis writes ...
>
>The 10D practice of showing a jpeg histogram, in spite of capturing in

>raw format, makes using a +1 exposure bias tricky ...
>I wonder if the $8000 EOS-1Ds Mark II offers better information.

I have a 1Ds and a 1D Mark II and I don't trust the histogram on those
either, for the same reasons. You eventually learn there's a 'fudge
factor' and only go so far to leave a bit of working room.

>With the 10D I've captured about 200 files using +1 exposure bias ...
>this kind of dynamic-range gain is a most interesting topic.

Here's another write-up on this which you may find interesting (I
haven't read the Fraser link yet so not sure how much is duplicated)
.... http://www.luminous-landscape.com/tutorials/expose-righ...

>Hopefully someone who has done similar experiments, or found
>reports on the topic, will chime in.

I ran some tests trying to decide if it were better to shoot metered at
a low ISO or to shoot with exposure compensation at higher ISO (ie, ISO
100 vs ISO 200 @ +1 vs ISO 400 @ +2 vs ISO 800 @ +3), with the
overexposure compensated for during RAW conversion (note you can only
do this with low contrast scenes since with a full tonal range you
start to clip with the + compensation). My conclusion was it made
little difference in image quality whether you shot at ISO 400 @ +2 and
adjusted during RAW conversion compared to shooting at ISO 100 at 0
compensation. The problem with +2 as you note is that you get close to
the right edge of the histogram and can clip a channel, so as a
practical matter if I have exposure room on the histogram to go +2 or
+1 I would just as soon lower the ISO instead and shoot at 0 (ie,
metered) at the same shutter speed.

You can check your camera to see if you get the same results ... here
are two links showing what I got ...

http://members.aol.com/bhilton665/iso800_200.jpg (shot a gray card at
800, 800 -2 exposure +2 RAW conversion, 800 +2 exposure -2 RAW
conversion and at 200. All should give roughly equivalent exposures
but note the 800 -2 exp/+2 RAW is the noisest, 800 @ 0 second noisest
(as predicted by the "expose right" articles), and 800 +2 exp/-2 RAW is
pretty similar to the ISO 200 shot, noise-wise.

http://members.aol.com/bhilton665/iso800_100.jpg ... 800 +3 exp -2.2
RAW to get the exposure right vs ISO 100 metered ... looking at the
histograms you can see you are getting close to the clipping point at
+3 with nothing brighter than a gray card so any scene that would have
a decent range of tonal values would already be clipping. It's simpler
for me to just lower the ISO and shoot as metered since I get the same
end results (maybe a little smoother at 100 in this sample ... YMMV
depending on your camera and RAW converter).

Pretty easy to run your own tests with your camera and a gray card.

Bill
Anonymous
May 9, 2005 10:38:12 PM

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

Bill Hilton wrote:
>
> I ran some tests trying to decide if it were better to shoot metered at
> a low ISO or to shoot with exposure compensation at higher ISO (ie, ISO
> 100 vs ISO 200 @ +1 vs ISO 400 @ +2 vs ISO 800 @ +3), with the
> overexposure compensated for during RAW conversion (note you can only
> do this with low contrast scenes since with a full tonal range you
> start to clip with the + compensation). My conclusion was it made
> little difference in image quality


It's not a big difference but I tried loading your test shots in
irfanview & boosting the contrast way way way up and there is a very
obvious differnce if you exaggerate it enough. But I agree, I can't tell
without that exaggeration, except of course the underexposed one. It may
be though that with a low contrast scene, you *would* want to increase
contrast significantly.

Here's my test on a D70 enlarged 200%:
<http://www.edgehill.net/1/?SC=go.php&DIR=Misc/photograp...;


> whether you shot at ISO 400 @ +2 and
> adjusted during RAW conversion compared to shooting at ISO 100 at 0
> compensation. The problem with +2 as you note is that you get close to
> the right edge of the histogram and can clip a channel, so as a
> practical matter if I have exposure room on the histogram to go +2 or
> +1 I would just as soon lower the ISO instead and shoot at 0 (ie,
> metered) at the same shutter speed.
>
> You can check your camera to see if you get the same results ... here
> are two links showing what I got ...
>
> http://members.aol.com/bhilton665/iso800_200.jpg (shot a gray card at
> 800, 800 -2 exposure +2 RAW conversion, 800 +2 exposure -2 RAW
> conversion and at 200. All should give roughly equivalent exposures
> but note the 800 -2 exp/+2 RAW is the noisest, 800 @ 0 second noisest
> (as predicted by the "expose right" articles), and 800 +2 exp/-2 RAW is
> pretty similar to the ISO 200 shot, noise-wise.
>
> http://members.aol.com/bhilton665/iso800_100.jpg ... 800 +3 exp -2.2
> RAW to get the exposure right vs ISO 100 metered ... looking at the
> histograms you can see you are getting close to the clipping point at
> +3 with nothing brighter than a gray card so any scene that would have
> a decent range of tonal values would already be clipping. It's simpler
> for me to just lower the ISO and shoot as metered since I get the same
> end results (maybe a little smoother at 100 in this sample ... YMMV
> depending on your camera and RAW converter).
>
> Pretty easy to run your own tests with your camera and a gray card.
>
> Bill
>

--
Paul Furman
http://www.edgehill.net/1
san francisco native plants
Anonymous
May 10, 2005 12:03:14 AM

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

Bill Hilton wrote:
> Here's another write-up on this which you may find interesting (I
> haven't read the Fraser link yet so not sure how much is duplicated)
> ... http://www.luminous-landscape.com/tutorials/expose-righ...

That's where I originally learned the "expose to the right" technique,
but the article places a lot of faith in the histogram that the camera
presents:


"But, we all know (or at least should by now) that the worst sin in
digital imaging is to blow out the highlights - just as it was when
shooting slide film. Once they're blown (past the right-hand edge of
the histogram) it's bye-bye data."
[...]
"The simple lesson to be learned from this is to bias your exposures so
that the histogram is snugged up to the right, but not to the point
that the highlights are blown. This can usually be seen by the flashing
alert on most camera review screens. Just back off so that the flashing
stops."


That's what I've been doing - if I see the camera indicating blown
highlights after the shot I will usually take the shot again with a
slight negative exposure correction... unless it's something
difficult/obvious like the sun hiding behind a tree branch.

One suggestion I've seen on another forum is to set your in-camera
defaults to produce a flatter, lower contrast image which will show a
less aggressive histogram. I'm going to do some experimenting with this
today, modifying the in-camera settings and trying various levels of
overexposure to see what happens.

> I ran some tests trying to decide if it were better to shoot metered
at
> a low ISO or to shoot with exposure compensation at higher ISO (ie,
ISO
> 100 vs ISO 200 @ +1 vs ISO 400 @ +2 vs ISO 800 @ +3), with the
> overexposure compensated for during RAW conversion (note you can only
> do this with low contrast scenes since with a full tonal range you
> start to clip with the + compensation). My conclusion was it made
> little difference in image quality whether you shot at ISO 400 @ +2
and
> adjusted during RAW conversion compared to shooting at ISO 100 at 0
> compensation.

For normal exposure times it probably doesn't make much difference, but
I've found that if you're planning to have your shutter open for
minutes, longer exposures at a lower ISO have less noise than shorter
exposures at a higher ISO. Makes sense: I believe that higher ISO in
camera is achieved by cranking up the analog gain.
Anonymous
May 10, 2005 2:11:18 AM

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

On 9 May 2005 12:06:48 -0700, googlegroups@sensation.net.au wrote:

>David Ellis wrote:
>> Bruce Fraser's white paper at
>>
>> http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf
>>
>> makes the case that half the information in a digital capture is in
>> the fifth, or highest, stop. And some digital cameras can capture and
>> image that is overexposed, thereby driving image information into
>that
>> often little-used last stop. The highlights, apparently blown out,
>can
>> be recovered in Photoshop's raw image converter.
>
>I've always wondered how this could be possible. 12 bits of
>information, if highlights are blown out then surely that means the
>level is at 4095 and can go no higher. How could you possibly 'recover'
>extra information from this?
>
>However ... after seeing this I finally understand why:
>
>"... so cameras show the histogram of the image after processing using
>the camera's default settings. Most cameras apply a fairly strong
>S-curve to the raw data so that the JPEGs have a more film-like
>response, with the result that the on-camera histogram often tells you
>that your highlights are blown when, in fact, they aren't."
>
>I'm a little miffed that my very expensive camera cannot accurately
>inform me of truly blown highlights.

The 10D practice of showing a jpeg histogram, in spite of capturing in
raw format, makes using a +1 exposure bias tricky because at the time
of shooting the amount of information spilled into the sixth stop (if
you'll allow that technical leap) cannot be gauged by viewing the LCD.
I wonder if the $8000 EOS-1Ds Mark II offers better information.

With the 10D I've captured about 200 files using +1 exposure bias (+2
is too extreme) and evaluative metering. About 10% of those have
pixels where at least one channel has a value of 255. Bill Hilton
pointed out, "If only one channel is clipped then any RAW converter
can salvage some data and reconstruct something." When two channels
are blown out, I'm finding the PS RIC reconstruction produces lower
quality than I would like, but it would be quite acceptable for
vacation snapshots.

For the files where the +1 exposure bias worked as expected , the
extra stop of dynamic range yields highlight detail in a sunny outdoor
scene shot through a window while showing shadow detail for the
interior room without flash fill. I've only achieved this before by
layering and masking in Photoshop two precisely-aligned images, one
exposed for highlight, the other for shadow. A tricky business if one
is shooting a basketball game. :=)

However, as "dylan" commented ("...not sure about the accuracy of the
result compared to the original."), I'm seeing problems with loss of
detail in yellow highlights even when the red and green channels are
clipped in very few pixels.

I may not be enough of a scientist to correctly evaluate what's
happening, but this kind of dynamic-range gain is a most interesting
topic. Hopefully someone who has done similar experiments, or found
reports on the topic, will chime in.
--David
Anonymous
May 10, 2005 3:17:07 PM

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

>Paul Furman
>Here's my test on a D70 enlarged 200%:
<http://www.edgehill.net/1/?SC=­go.php&DIR=Misc/photography/ex­pose-right>


These seem a good bit noiser at 200% than the 1D Mark II shots I posted
at 400%, at least to my eyes.
Anonymous
May 10, 2005 11:25:48 PM

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

Bill Hilton wrote:

>>Paul Furman
>>Here's my test on a D70 enlarged 200%:
>
> <http://www.edgehill.net/1/?SC=�go.php&DIR=Misc/photography/ex�pose-right>
>
>
> These seem a good bit noiser at 200% than the 1D Mark II shots I posted
> at 400%, at least to my eyes.


Yep, they are indeed! Less than 1/4 the price though. I would love to
see this kind of test done under controlled conditions for a bunch of
different cameras. It is very revealing. This plus a crop of a
complicated scene would make an extremely valuable comparison chart.


--
Paul Furman
http://www.edgehill.net/1
san francisco native plants
Anonymous
May 11, 2005 4:21:15 AM

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

On 9 May 2005 20:03:14 -0700, googlegroups@sensation.net.au wrote:

>Bill Hilton wrote:
>> Here's another write-up on this which you may find interesting (I
>> haven't read the Fraser link yet so not sure how much is duplicated)
>> ... http://www.luminous-landscape.com/tutorials/expose-righ...
>
>That's where I originally learned the "expose to the right" technique,
>but the article places a lot of faith in the histogram that the camera
>presents:
>
>
>"But, we all know (or at least should by now) that the worst sin in
>digital imaging is to blow out the highlights - just as it was when
>shooting slide film. Once they're blown (past the right-hand edge of
>the histogram) it's bye-bye data."
>[...]
>"The simple lesson to be learned from this is to bias your exposures so
>that the histogram is snugged up to the right, but not to the point
>that the highlights are blown. This can usually be seen by the flashing
>alert on most camera review screens. Just back off so that the flashing
>stops."

I also learned "expose to the right" at luminous-landscape. But the
"Just back off so that the flashing stops" troubled me because
retaining the flashing is precisely what's required to gain the
benefits of using positive exposure bias in the camera and negative
exposure values in the raw image converter.
>
>
>That's what I've been doing - if I see the camera indicating blown
>highlights after the shot I will usually take the shot again with a
>slight negative exposure correction... unless it's something
>difficult/obvious like the sun hiding behind a tree branch.
>
It is the high-contrast scene that utilizes the expose-to-the-right
technique.
<snip>

Because of my limited experience with this subject, I had trouble
relating to the 18% gray test targets in the other article. A regular
photo is easier for me to follow.

At www.ellisisle.com/raw_image_tests see a single raw file, processed
a variety of ways. After exposure the 10D's Info LCD had lots of
flashing. I suggest you open all four .htm files on screen together,
each in a tab or its own window, for comparison purposes.

The images show the difference between dealing with apparently
blown-out highlights in Photoshop Curves (2.htm) and dealing with them
in the raw image converter (3.htm and 4.htm). The latter provides
highlight detail recovery in an apparently overexposed image that
cannot be achieved with Photoshop Curves.

The broad tonal range in 4.htm is dependent on having the 10D's
blown-out highilght indication flashing.
--David
Anonymous
May 11, 2005 4:21:16 AM

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

David Ellis wrote:
>
> It is the high-contrast scene that utilizes the expose-to-the-right
> technique.


Hmm, interesting, I see what you mean from the example.


>
> At www.ellisisle.com/raw_image_tests see a single raw file, processed
> a variety of ways. After exposure the 10D's Info LCD had lots of
> flashing. I suggest you open all four .htm files on screen together,
> each in a tab or its own window, for comparison purposes.
>
> The images show the difference between dealing with apparently
> blown-out highlights in Photoshop Curves (2.htm) and dealing with them
> in the raw image converter (3.htm and 4.htm). The latter provides
> highlight detail recovery in an apparently overexposed image that
> cannot be achieved with Photoshop Curves.


The real surprise in that set is between 2 & 3
http://ellisisle.com/raw_image_tests/2.htm
http://ellisisle.com/raw_image_tests/3.htm

I'm confused though because the dark interior areas are the same in
these two. This doesn't make sense.


>
> The broad tonal range in 4.htm is dependent on having the 10D's
> blown-out highilght indication flashing.


4 has the shaded areas lost in black which is what I would expect.


--
Paul Furman
http://www.edgehill.net/1
san francisco native plants
Anonymous
May 11, 2005 4:20:04 PM

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

INteresting and educational discussion! Thanks.

On Sun, 08 May 2005 04:18:34 GMT, David Ellis <nospam@everywhere.com>
wrote:

>Bruce Fraser's white paper at
>
>http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf
>
>makes the case that half the information in a digital capture is in
>the fifth, or highest, stop. And some digital cameras can capture and
>image that is overexposed, thereby driving image information into that
>often little-used last stop. The highlights, apparently blown out, can
>be recovered in Photoshop's raw image converter.
>
>Using a Canon EOS 10D, I've tried this with some amazingly good
>results and some poor results. I'd like to hear about your 10D
>experience in this area.
>
>--David
Anonymous
May 12, 2005 4:45:58 AM

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

In message <mf-dnSrJYKSq8BzfRVn-tQ@speakeasy.net>,
Paul Furman <paul-@-edgehill.net> wrote:

>Yep, they are indeed! Less than 1/4 the price though. I would love to
>see this kind of test done under controlled conditions for a bunch of
>different cameras. It is very revealing. This plus a crop of a
>complicated scene would make an extremely valuable comparison chart.

It would be more illuminating about the camera *hardware* if you looked
at the RAW data. Every RAW conversion is different. You can look at
the red and blue channels of the RAW as a simple bitmap; the green is a
little special with bayer, and must be rotated to make a normal bitmap.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
May 12, 2005 4:46:58 AM

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

In message <1115684451.130118.226590@z14g2000cwz.googlegroups.com>,
"Bill Hilton" <bhilton665@aol.com> wrote:

>I ran some tests trying to decide if it were better to shoot metered at
>a low ISO or to shoot with exposure compensation at higher ISO

I asked once before, but you never replied; what are you measuring with
a grey card? A grey card tells you almost nothing about *posterization*
of the shadows, the biggest enemy of low RAW levels.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
May 12, 2005 4:46:59 AM

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

JPS@no.komm wrote:
>
> A grey card tells you almost nothing about *posterization*
> of the shadows, the biggest enemy of low RAW levels.


When I (heavily) boosted contrast in his samples, posterization was the
big noticeable difference.

--
Paul Furman
http://www.edgehill.net/1
san francisco native plants
Anonymous
May 12, 2005 4:58:40 AM

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

In message <1115694194.665173.215570@z14g2000cwz.googlegroups.com>,
googlegroups@sensation.net.au wrote:

>One suggestion I've seen on another forum is to set your in-camera
>defaults to produce a flatter, lower contrast image which will show a
>less aggressive histogram. I'm going to do some experimenting with this
>today, modifying the in-camera settings and trying various levels of
>overexposure to see what happens.

That pretty much works with the Canons, as far as that goes. -2
contrast in the camera (set for JPEGs) pretty much has the clipping
point of the histogram right about where the most sensitive color
channel will clip with a white highlight (if the WB setting is correct).
That is usually green, and the blue may go another half stop, and the
red may go another stop, with "daylight" balance. Red goes further with
the cooler WB settings, and the blue goes further with the warmer ones.
Theoretically, you could put a cyan-blue filter on the camera, and shoot
greyscale scenes with much more than 12-bits of luminance levels, but of
course, the highlights will be red-sensitive only.

Of course, a true RAW RGB histogram would be so convenient, but the
manufacturers don't seem to care if we can optimize our exposure.

In fact, the flash units for most digitals should give off magenta
light. I've put magenta filters made from "Flomo" transparent binders
over my 550EX, and had a grey card give RAW levels within 10% for all
three channels. The manufacturers are sleeping, and dreaming about
digital "film". Where are the tungsten and daylight lens filters,
adjusted for CFA sensitivities?
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
May 15, 2005 6:13:11 PM

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

> John P Sheehy writes
>
> I asked once before, but you never replied; what are you measuring
> with a grey card?

I thought it was obvious ... measuring noise.
Anonymous
May 16, 2005 2:10:36 AM

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

In message <1116191591.026891.236820@o13g2000cwo.googlegroups.com>,
"Bill Hilton" <bhilton665@aol.com> wrote:

>> John P Sheehy writes
>>
>> I asked once before, but you never replied; what are you measuring
>> with a grey card?
>
>I thought it was obvious ... measuring noise.

I know what you're trying to measure. I am asking why you think this is
a comprehensive test for the issue of variable ISO with fixed exposure.

The alleged (and real) benefit of shooting at ISO 1600 and +2 as opposed
to ISO 400 and 0 EC is for the shadows; mainly the deeper shadows, *OR*
low-contrast midtones and highlights restored to high contrast with PP.
In other words, it is to avoid posterization.

Exposing a grey card is not *supposed* to show the more important
benefits. Also, you never know how much the RAW conversion obliterates
detail along with noise, if there is no detail that you can lose.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
!