Re: [APML]: Stacking images in photoshop

[Wil Milan <wmilan@airdigital.com>]

Chuck Vaughn wrote:

> >Using an image-processing package which allows 16-bit or larger pixel values
> >avoids this by capturing the full value of multiple summed images. Some
> >scientific-imaging packages also allow pixels to be respresented by 16- or 32-bit
> >floating-point values, which has advantages for some kinds of numerical
> >processing.
> >
> This may or may not be true. The 8 bits are likely to be the most significant
> bits and 16 bits simply allows finer resolution. Finer resolution is indeed useful
> such as in contrast stretching but does not increase dynamic range (which is what
> we're talking about here) if 8 bits already covers the available range.

You're correct that stacking images does not increase the absolute dynamic range, but
it does increase the range of resolution, which is the reason for doing it. In
conventional stacking that additional range is thrown away in favor of increasing
contrast, but with a larger bit depth (16 bits per channel instead of 8, for instance)
you can have your cake and eat it too -- gain the contrast when needed *without*
throwing away the extra resolution. It represents information retained instead of
lost, which is always to the good.

Wil M.
--
"When I consider your heavens, the work of your fingers, the moon and the stars which
You have set in place, what is Man that you are mindful of him, or the son of Man that
you care for him?"  -- Psalm 8