On May 26, 2004, at 4:40 PM, Moose wrote:
> I have PS7 and can handle 48 bit images. What I have found to be true
> for me is that 48 bit doesn't really add anything if I adjust the scan
> to a good histogram and reasonable color balance at the preview stage
> before scanning. After experimenting with this issue, I concluded
> that 24 bits is enough to capture all the color/tonal nuance that I
> can distinguish on my monitor and prints.
Both your monitor and printer are only capable of displaying in 24-bit
colour, that's why you don't see a difference. As well, 48-bit colour
resolves more colour detail than can be discerned by the human eye so
you don't see any difference. The advantage comes in heavy editing,
which you mention further along.
> The problem with 24 bit comes when the white and black points aren't
> set right in the scan. Then data from the top and/or bottom of the
> luminance ranges are thrown away in the editor (yup, that's what the
> Auto functions and Manual adjustment of the histogram in the editor
> do.), forcing interpolation of less than 24 bits of data up to 24
> bits.
Yes exactly. I recently ran into this problem in a dramatic fashion.
I'm working on restoring an old tintype photo (my guess is it's from
around the 1880's). This is mostly just a personal project as well as
some work for a photoshop class I'm taking. I don't have a flatbed
scanner so I had to use one of the scanners at the school which can
only do 24-bit colour. Because the tintype is so dark, it needed a lot
of tonal adjustment to get it back to a more or less neutral image (I
left a bit of a colour cast to preserve some of the old-fashioned
look). In levels, I had to drag the white point to 124 (from 255) to
reach the first data in the image itself. That means that I'm throwing
away more than half of the colour data from the image. If I had a
48-bit scan there would still have been enough colour data remaining to
map out to a full 24-bit range of colour.
Andrew "Frugal" Dacey
frugal@xxxxxxxxxxxxxxx
http://www.tildefrugal.net/
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