Message-Id: <mailto:199409141231.HAA07865@library.wustl.edu> Date: Tue, 13 Sep 1994 13:43:03 CDT From: John Grossman <mailto:grossman@UTMDACC.MDA.UTH.TMC.EDU> Subject: Re: IMAGELIB Digest - 11 Sep 1994 to 12 Sep 1994 To: Multiple recipients of list IMAGELIB <mailto:IMAGELIB@ARIZVM1.BITNET>
>A contributor wrote:
>8-bit vs. 24-bit color.
>
>I have a garden-variety Dell computer with a 17" monitor and graphics card
>capable of displaying 24-bit color. I delight in displaying an 8-bit color
>and a 24-bit color version of the same image side by side and having the
>viewer tell the difference. (I did this at a conference and most people
>guessed it wrong.)
>
>Of course there is a difference, and if you get up close and look at areas
>of slowly changing color (sky is a good example) you can see the difference.
>But, for everyday use at normal viewing distances, the factor of 3 savings in
>size is worth while.
I wish 8-bit color were good enough for everyday use at normal viewing distances. To see why it isn't try this on either a Mac or a Windows machine with 8-bit color: Using an image viewing program that allows you to have multiple image windows open simultaneously, open a grayscale image (black and white photograph, for example) and a color photograph with a reasonable range of colors (a portrait of a person in a room environment). You'll note that the face looks horrible when you make the grayscale image the active window and the grayscale image looks horrible when you make the color photograph the active window.
This problem will drive you crazy if you're trying to do any kind of work that involves looking at images with substantially different color palettes. Examples include reviewing image archives and doing medical work with both radiographs and pathology images.
I think the standard for everyday use should be something that gives us the kind of visual experience that we have in everyday life. That often includes looking at pictures and objects with widely varying palettes. Even 16 bit color is not adequate for this purpose. Standard 16 bit color only uses 5 bits each of R, G, and B per pixel. This means that a 256 shade gray scale image must be rendered with only 32 shades of gray. Try that with any full range gray scale image and you'll see how bad it looks. Ironically, 8-bit displays usually perform better than 16-bit displays for gray scale images because they change the CLUT to 256 grays.
____________________________________________________________________________ John Grossman Project Director, The Radiologic-Pathologic Institute The University of Texas M. D. Anderson Cancer Center Phone 713-792-6214 FAX 713-792-0811