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I recall reading that making an exposure with the lens cap on, then
combining it with the image exposure is a good way to eliminate or at least
reduce long exposure noise. What I don't remember is which blending mode
should be used. Anyone know?

Thanks,
Cooter

"Cooter" <> wrote in message
news:Fn8rb.81532$. com...
> I recall reading that making an exposure with the lens cap on, then
> combining it with the image exposure is a good way to eliminate or at
least
> reduce long exposure noise. What I don't remember is which blending mode
> should be used. Anyone know?

I don't think that will work with random noise.

"Charles Schuler" <> wrote
>
> "Cooter" <> wrote in message
> news:Fn8rb.81532$. com...
> > I recall reading that making an exposure with the lens cap on, then
> > combining it with the image exposure is a good way to eliminate or at
> least
> > reduce long exposure noise. What I don't remember is which blending mode
> > should be used. Anyone know?
>
> I don't think that will work with random noise.

It works for getting rid of hox pixel noise, if your camera doesn't have
built-in noise reduction.

From what I understand, smaller CCD cameras generate random noise with
longer exposures at high ISO that can be minimized by keeping the CCD cooler
(turn off the camera for a few minutes between pictures), use a tripod and
turn anti-shake features off (in the case of the A1), use lower ISO where
possible, use a flash instead of long exposures.

I agree with the others that the method you are describing is for hot
pixels.

If you take pictures that can't work around the noise issue, noise can be
reduced with software such as:

http://www.neatimage.com/ (Neat Image)
http://www.picturecode.com/ (Noise Ninja)

Scott

"Cooter" <> wrote
> I recall reading that making an exposure with the lens cap on, then
> combining it with the image exposure is a good way to eliminate or at
least
> reduce long exposure noise. What I don't remember is which blending mode
> should be used. Anyone know?
> Thanks,
> Cooter

In article <Fn8rb.81532$> ,
says...
> I recall reading that making an exposure with the lens cap on, then
> combining it with the image exposure is a good way to eliminate or at least
> reduce long exposure noise. What I don't remember is which blending mode
> should be used. Anyone know?
>
> Thanks,
> Cooter
>
>
>

When I'm taking long exposures I take one picture with the lens cap on
and the next of the object I'm photographing. Two things to keep in mind
are that both pictures should be taken at the same shutter speed and you
should set your camera to save the file in a non-compressed format such
as TIFF. Saving as a Jpeg adds jpeg artifacts to the noise. With daylight
or flash pictures this isn't ussually a problem.

After the pictures are in your computer load them into a editing program
that supports layers such as Photoshop. Load the good exposure then into
a seperate layer load the exposure with the lens cap on. Subtract this
one from the good layer and most of the niose should be eliminated. Save
this file under a different name than you original picture.


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That only works with fixed pattern noise, which is not the sort that
bothers you in long exposures.

Cooter wrote:
>
> I recall reading that making an exposure with the lens cap on, then
> combining it with the image exposure is a good way to eliminate or at least
> reduce long exposure noise. What I don't remember is which blending mode
> should be used. Anyone know?
>
> Thanks,
> Cooter

--
Don Stauffer in Minnesota

webpage- http://www.usfamily.net/web/stauffer

On Sat, 08 Nov 2003 15:57:25 GMT, in rec.photo.digital "Cooter"
<> wrote:

>I recall reading that making an exposure with the lens cap on, then
>combining it with the image exposure is a good way to eliminate or at least
>reduce long exposure noise. What I don't remember is which blending mode
>should be used. Anyone know?

Give the Neat Image demo a try.
__________________________________________________ ______
Ed Ruf Lifetime AMA# 344007 ()
http://members.cox.net/egruf
See images taken with my CP-990 and 5700 at
http://members.cox.net/egruf-digicam

Take a look at "Black Frame" free from MediaChance:
http://www.mediachance.com/digicam/blackframe.htm

Good Luck!

"Don Stauffer" <> wrote in message
news:...
> That only works with fixed pattern noise, which is not the sort that
> bothers you in long exposures.
>
> Cooter wrote:
> >
> > I recall reading that making an exposure with the lens cap on, then
> > combining it with the image exposure is a good way to eliminate or at
least
> > reduce long exposure noise. What I don't remember is which blending mode
> > should be used. Anyone know?
> >
> > Thanks,
> > Cooter
>
> --
> Don Stauffer in Minnesota
>
> webpage- http://www.usfamily.net/web/stauffer