Olympus-OM
[Top] [All Lists]

Re: [OM] somewhat OT: 24bit vs higher color

Subject: Re: [OM] somewhat OT: 24bit vs higher color
From: "Paul D. Farrar" <farrar@xxxxxxxxxxxx>
Date: Sun, 24 Sep 2000 18:39:24 -0500
At 08:10 AM 9/24/00 -0700, you wrote:
>>if stuff on the web displays (generally) only in 24bits, and i think PS
>>and other image editing software also works in 24bits, what's the use of
>>scanning at higher depth? if there were two pictures, side by side, 24 and
>>36 (or 32, if the monitor is limited to 32), can one visually discern
>>it?
>
>The only useful reason to scan at higher bit depths is if you are 
>going to manipulate the image, especially the value curves.
>
>There is no visible difference between the two initially, but 
>differences can build up more readily in 24 bit images when you apply 
>multiple edits.
>
>For example, let's just say you have a B&W image with a value range 
>of 1 to 100, but only values from 26 to 75 are represented. You 
>adjust the curves to "normalize" the value range, perhaps through 
>auto levels or auto contrast. The image values now have a "comb" look 
>in histograms, with all the odd or even values missing.
>
>Now lets say you do your value adjustment on a scale from 1 to 1000 
>on values that range from 261 to 750. Afterward, you still have 
>combed data, with only even or odd values, but now you reduce it to 
>the "normal" 1 to 100 range, and every value is represented.

They don't dither? They should - on both upconversion and downconversion.

Paul

>
>For the best precision, do as much editing you can in 48 bits -- 
>especially global curves -- then reduce to 24 bits. Of course, 
>scanner software is supposed to do this.
>
>-- 
>: Jan Steinman <mailto:Jan@xxxxxxxxxxxxxx>
>: Bytesmiths <http://www.bytesmiths.com>
>
>< This message was delivered via the Olympus Mailing List >
>< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
>< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
>


< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz