Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!news.cs.indiana.edu!arizona.edu!ece.arizona.edu!dan From: dan@ece.arizona.edu (Dan Filiberti) Newsgroups: comp.sys.next Subject: Re: ColorStation questions Message-ID: <1991May1.133326@ece.arizona.edu> Date: 1 May 91 20:33:26 GMT References: <1991Apr24.231003@ece.arizona.edu> <1991Apr25.180420.9712@menudo.uh.edu> <1991Apr25.221947@ece.arizona.edu> <1991Apr30.150026.9826@magnus.acs.ohio-state.edu> Reply-To: dan@ece.arizona.edu (Dan Filiberti) Distribution: usa,local Organization: University of Arizona Dept. of Electrical and Computer Engineering Lines: 108 Nntp-Posting-Host: dialsun.ece.arizona.edu In article <1991Apr30.150026.9826@magnus.acs.ohio-state.edu>, mitroo@magnus.acs.ohio-state.edu (Varun Mitroo) writes: |> What are you saying? Yes, the colorstation has "only" |> 4096 colors. You may want to study a little more about |> color on computers before you make comments like this. |> 4 bits/pixel gives 16 shades of a pure color. However, |> these 16 shades are not best represented by linear |> differences between them. (ie intensity 8 is not twice |> as bright as intensity 4). These colors must be adjusted |> to appear as distinct from each other as possible. This |> is called gamma correction, I believe. So, what's your dumb point. Gamma correction compensates for the nonlinearity of the display device. By making the colors appear "as distinct from each other as possible", you are essentially making it linear. This does not necessarily require a CLUT. The 4 bit "quantization", a term you should look up, divides the RGB color cube evenly. The digitized colors are best represented linearly, but not necessarily best viewed linearly on the display (the human visual system is best represented by a nonlinear color space). Here's a quote from "Fundamentals of Digital Image Processing" by Jain, a book which I suggest you read... "In the NTSC color coordinate R, G, B system, the reproducible color gamut is the cube [0,1]X[0,1]X[0,1]. It has been shown that uniform quantization of each color coordinate in this system provides the best results as compared to uniform quantization in several other coordinate systems. Four bits per color have been found to be just adequate in this coordinate system." The analog RGB signal is sampled, then quantized to 4bits, as above. Whether or not the 4096 colors chosen by NeXT map these color to best represent the human visual system (CIE coordinates) is irrelevant. What the camera sees, is quantized to 4 bits, and thats what research has with which to start. After all, just because you can't see a color doesn't mean that it doesn't exist in the image. |> Does resolution have anything to do with this? Do you |> have any idea what you're talking about? Since when is |> skin predominantly red?? Could it possibly have |> a tinge of blue? If it does, you have effectively |> doubled the number of colors from 16 to 32. How about |> a greenish tinge? Maybe you could have imparted this |> wisdom to Cezanne or Rembrant to always paint skin red |> rather than worrying about "warm" and "cool" colors. Talking about "faulty and ignorant"! This doesn't even deserve a reply, but in order to augment your thinking, I will. 1. Does resolution have anything to do with this? I don't know, that's what the research is supposed to determine. Can you prove that it does or doesn't? I'd like to see your evidence. 2. Since when is skin predominantly red?? Since studies have shown that the red component in skin color is always of higher intensity than green and blue, and is important in diagnosis of skin disorders. Take an image of a part of your skin, and view the rgb histograms. Which intensity is higher, that's right red. Now convert to IHS space and look at the hue. The hue lies in the red-purple range. 3. How about a greenish tinge? You have predominantly green and blue skin? Maybe you would be a good candidate for a research subject. And the doubling of colors ( there is some blue hue, but not much) is the problem, as I stated in my previous post. 4. ..."warm" and "cool" colors. These warm and cool colors that painters use for skin (tan, brown, pink, whatever) all contain a higher red component than blue and green, dummy. And, besides, what does a painting have to do with skin imaging? |> Before you make these idiotic claims, you might try |> any or all of the following: |> 1. Study a little bit about how the human visual |> system works |> 2. Read a little bit about color theory |> 3. Read a computer graphics textbook concerning color |> representation/dithering/anti-aliasing |> 4. Go to an art museum and look carefully at some |> portraits - maybe even look at some paintings |> by Seurat |> 5. Buy a copy of Frank Netter's Atlas of Human Anatomy |> and look at some of his illustrations of skin |> 6. Actually look at a colorstation screen Maybe you should follow some of your own advise (1,2,3). Research dealing with skin images doesn't start with viewing portraits and illustrations (4,5). And, I've seen the colorstation screen (6). Whether this screen is overkill when it comes to diagnosis of skin images remains to be researched, maybe a 256 color palette is enough. Why all the extra cost? And, if you think you have the answer, please post some of the research you have done, or some papers that you have seen on the subject. After all, put up or shut up. From what I've read, you should definitely do the latter. Daniel Filiberti dan@helios.ece.arizona.edu