Canon 20D noise reduction at high ISO's

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

Winston wrote:
> On my 20D there's a custom function to reduce noise at high ISO's.
I'm
> curious why this is a custom function & not built into the firmware
> already? When *wouldn't* you want the noise suppression turned on at
> ISO's of 1600 & 3200?
>
> Thanks,
> Winston
You can get artifacts when using noise reduction, most of us would
rather control how the noise reduction is used, if at all, in a program
like PhotoShop. If you are going to be making prints often what looks
like a lot of noise on the computer screen is not noticeable on the
print.

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

You can lose sharpness and texture and everything will become smooth and
plastic looking. It is one of those features that you use if there is no
opportunity to edit the photo properly later.

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

On my 20D there's a custom function to reduce noise at high ISO's. I'm
curious why this is a custom function & not built into the firmware
already? When *wouldn't* you want the noise suppression turned on at
ISO's of 1600 & 3200?
------------------------

There is no such Custom Function on the 20D.
CF-2 reduces noise in long exposures, not high ISO's.
This dark-frame subtraction technique is useful for
astro-photographers. The drawback is that it takes longer between
shots. For example, if you shoot a 3-minute exposure it will take
another 3 minutes for the buffer to clear so you can take the next
shot.

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

In article <1108673451.748213.201700@f14g2000cwb.googlegroups.com>,
bobo44039@yahoo.com says...
> On my 20D there's a custom function to reduce noise at high ISO's. I'm
> curious why this is a custom function & not built into the firmware
> already? When *wouldn't* you want the noise suppression turned on at
> ISO's of 1600 & 3200?
>
> Thanks,
> Winston

I'm not sure if you're referring to dark frame subtraction or image-
smothering noise reduction.

Dark frame subtraction will reduce noise, but doubles the exposure time.

Smothering noise reduction smooths the luminance to reduce the
appearance of noise. Fine details, colors and such get smeared.
--
http://www.pbase.com/bcbaird/

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Scott W wrote:

>
> If you are going to be making prints often what looks
> like a lot of noise on the computer screen is not noticeable on the
> print.

No way! 200% crops are the only way to judge image quality!!

At least that's what I keep getting told, guess I need to stop looking at my
prints? :-)

--

Stacey

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

"Annika1980" <annika1980@aol.com> writes:

>There is no such Custom Function on the 20D.
>CF-2 reduces noise in long exposures, not high ISO's.
>This dark-frame subtraction technique is useful for
>astro-photographers. The drawback is that it takes longer between
>shots. For example, if you shoot a 3-minute exposure it will take
>another 3 minutes for the buffer to clear so you can take the next
>shot.

It's not "waiting for the buffer to clear". It's taking a second
exposure, identical in length to the first, then reading it out as an
image in order to subtract it from the first image. That's why it takes
twice the time.

Dave

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

>When *wouldn't* you want the noise suppression turned on at
>ISO's of 1600 & 3200?

There's usually a menu setting for noise reduction that's meant for
in-camera jpeg conversions. I'd probably use it for that, if I ever
shot jpegs ... but if you shoot RAW mode it's irrelevant, you would do
your noise filtering either during the RAW conversion (depending on the
software) or you'd convert w/o filtering and run the filtering with a
3rd party tool like Noise Ninja or Neat Image, which gives you a lot
more control than using the in-camera preset. I use Neat Image and it
does a very nice job on high ISO images.

Bill

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Winston:
> On my 20D there's a custom function to reduce noise at high ISO's. I'm
> curious why this is a custom function & not built into the firmware
> already? When *wouldn't* you want the noise suppression turned on at
> ISO's of 1600 & 3200?

You have misunderstood the function. It is noise reduction for long
exposures. Astrophotographers like me
<http://www.davidillig.com/ast-m42m45050127.shtml&gt; use it because we
make exposures of up to five minutes. With noise reduction on, after
completing a four-minute (e.g.) exposure the camera makes another
four-minute exposure with the shutter closed. This is called a "dark
frame." The camera then subtracts the dark frame -- specifically, the
thermal and other noise that it contains -- from the four-minute
exposure. Thus a four-minute exposure with noise reduction turned on
requires a bit over eight minutes to complete. Some astrophotographers
prefer to make their own dark frames -- exposures the same length as
the light exposure, but with the optics completely closed off -- and
subtract them with the image-processing software, be it Photoshop or
Images Plus or other.

Davoud

--
usenet *at* davidillig *dawt* com

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"Davoud" <see@below.net> wrote in message
news:190220051631034090%see@below.net...
> Winston:
>> On my 20D there's a custom function to reduce noise at high ISO's. I'm
>> curious why this is a custom function & not built into the firmware
>> already? When *wouldn't* you want the noise suppression turned on at
>> ISO's of 1600 & 3200?
>
> You have misunderstood the function. It is noise reduction for long
> exposures. Astrophotographers like me
> <http://www.davidillig.com/ast-m42m45050127.shtml&gt; use it because we
> make exposures of up to five minutes. With noise reduction on, after
> completing a four-minute (e.g.) exposure the camera makes another
> four-minute exposure with the shutter closed. This is called a "dark
> frame." The camera then subtracts the dark frame -- specifically, the
> thermal and other noise that it contains -- from the four-minute
> exposure. Thus a four-minute exposure with noise reduction turned on
> requires a bit over eight minutes to complete. Some astrophotographers
> prefer to make their own dark frames -- exposures the same length as
> the light exposure, but with the optics completely closed off -- and
> subtract them with the image-processing software, be it Photoshop or
> Images Plus or other.
>
> Davoud
>
> --
> usenet *at* davidillig *dawt* com

I guess the word noise is missleading.

Strictly, noise is a random process and will be different in the main
exposure and the dark frame on a pixel by pixel basis.

What the dark frame subtraction is removing is the pixel to pixel dark
current level, this is an offset or bias in statistics terms, not noise.

In fact as the actual random noise will be different in the two frames, the
noise variance across the pixels will be doubled by this process, so don't
use "noise reduction" unless your exposures are long enough for the pixel
dark current to be visible.


Lester

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

In article <190220051631034090%see@below.net>, see@below.net (Davoud)
wrote:
> make exposures of up to five minutes. With noise reduction on, after
> completing a four-minute (e.g.) exposure the camera makes another
> four-minute exposure with the shutter closed. This is called a "dark
> frame."
Wouldn't any target have moved significantly in that 10 min time or do you
use mounts that track with the target?

Iain

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

In article <memo.20050221231533.2448E@ilba14195.www.blueyonder.co.uk&gt;,
i.laskey@blueyonder.co.uk (Iain Laskey) wrote:

> In article <190220051631034090%see@below.net>, see@below.net (Davoud)
> wrote:
> > make exposures of up to five minutes. With noise reduction on, after
> > completing a four-minute (e.g.) exposure the camera makes another
> > four-minute exposure with the shutter closed. This is called a "dark
> > frame."
> Wouldn't any target have moved significantly in that 10 min time or do you
> use mounts that track with the target?
>
> Iain

You need a tracking mount for just about all astrophotography.

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

"Iain Laskey" <i.laskey@blueyonder.co.uk> wrote in message
news:memo.20050221231533.2448E@ilba14195.www.blueyonder.co.uk...
> In article <190220051631034090%see@below.net>, see@below.net (Davoud)
> wrote:
> > make exposures of up to five minutes. With noise reduction on, after
> > completing a four-minute (e.g.) exposure the camera makes another
> > four-minute exposure with the shutter closed. This is called a "dark
> > frame."
> Wouldn't any target have moved significantly in that 10 min time or do you
> use mounts that track with the target?
>
> Iain

The target may have moved, but the hot pixels will be in the same place.

Read 'shutter closed'...