Jawed wrote:
> I would agree with this. The intention is quite
> clearly to make the data fill the range of possible
> values. For reasons analogous to the use of 16-bit
> scans (really 10, 12 or 14 bits, generally): to
> maximise tonal smoothness and provide resilience
> under further editing.
Maybe I'm misreading this, but something I've wondered is whether any scanners
actually remap the data. It's hard to describe without a diagram - suppose
you have a monochrome scanner with an 8 bit A/D. The A/D can only produce
numbers from 0 to 255. If the actual image information is all between (say)
10 and 245 then you've effectively lost 8% of the resolution possible from
8 bits. But if you remap that range so that 10->0 and 245->255, you're
"stretching" the values in between. I presume this "stretching" is what
adjusting levels actually does. But presumably the fewer bits from the
A/D, and the smaller the input range, the poorer the result would be.
Does setting the black and white points cause the data to be remapped?
I presume this remapping is always post A/D. Are there any scanners which
attempt to adjust the input levels to maximise the range of values from
the A/D?
As far as I can tell, setting the black and white points in (say) Nikonscan
is no different to doing the same thing to a "flat" file in Photoshop with
Levels? BTW as far as colour shifts are concerned, I found Picture Window
Pro's ability to do levels in colour spaces other than RGB helped a lot.
RGB levels in PS tends to shift the colour balance, but HSL levels in PWP
doesn't.
What am I missing here?
Rob
Rob Geraghty harper@wordweb.com
