Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" <darkroom@i...> 
wrote:
 
> Why not?  You SHOULD be seeing only the top 8 significant bits of the 
image file.  What else would it do?

You are seeing 65000 levels represented as 256. As I said, if Photoshop 
could draw a black line in the Histogram for every level, you'd need a display 
that is about 30 feet long! With the current Histogram, you are viewing 256 
steps (they may be black, they may be white) but one level is drawn in that 
small GUI. So when you work with high bit files, the Histogram isn't "accurate" 
because thousands of levels are being represented as one level. 
 
> I don't understand how that follows.  Unless either the 16 bit histogram
> does not simply use the top 8 bits, or the conversion from 16 to 8 bits
> somehow does some "processing", and not simply uses the top 8 bits, then
> they should be the same.

All the additional data is there, you are just not seeing it. 

High bit files are like a stair case. An 8 bit file and a 16 bit file can be the same 
"length". But the 8 bit file has 256 steps to get from black to white while the 16 
bit stair case has 64500 (plus or minus). 

> Why?  Specifically.

You have more steps of data so as you move the levels, curves whatever, and 
then you drop down to 8 bits, Photoshop uses the BEST steps to compress 
the data down to 8 bits pre color. It uses the 645000 steps to end up with the 
best 256.