raz@kilowatt.uucp (Raz- Berry) (04/26/89)
Calling all GRAPHICS GURU's. I am in the process of adding the
ability of doing HAM pics' to iff2sun. Unfortunately I have very
little idea on how to compress a color map. I need a basic flowchart
on taking a 4096 color palette and converting it down to
256. Initially I was thinking that:
1) Sort the file by pixel color (emulating HAM mode of course).
eg. how many reds? how many purples? how many puke greens?
2) take the largest number of pixels per color, and assign them their
very own color register (up to 256).
3) take any remaining colors (if we have exceeded the 256 available colors)
and perform the 'best fit' with the current palette.
Assuming for the moment that this is the correct way to go, could some
kind soul clue me in to the appropiate 'best fit' for a palette
algorithim?
I am not real fond of the approach I have described above. If you have a
better method PLEASE let me know.
Ideas appreciated. I'll even consider a graphics reference book if you
know of one.
--
Steve -Raz- Berry Disclaimer: I didn't do nutin!
UUCP: sun!kilowatt!raz ARPA: raz%kilowatt.EBay@sun.com
"Fate, it protects little children, old women, and ships named Enterprize"ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) (04/27/89)
In article <33747@kilowatt.uucp> raz@kilowatt.uucp (Raz- Berry) writes: > I need a basic flowchart > on taking a 4096 color palette and converting it down to > 256. Initially I was thinking that: > > 1) Sort the file by pixel color (emulating HAM mode of course). > eg. how many reds? how many purples? how many puke greens? > 2) take the largest number of pixels per color, and assign them their > very own color register (up to 256). > 3) take any remaining colors (if we have exceeded the 256 available colors) > and perform the 'best fit' with the current palette. > Permit me to poke a hole in this. Suppose I have a simple HAM picture. The left half of the screen is various hues of purple, and the right half of the screen is various hues of blue. Separating these two fields is a vertical line, one pixel wide, that is solid white. Now, if you were to do a histogram on this image, you'd probably find the most popular 256 entries were hues of purple and blue, and white would be right at the bottom of the list. However, that white line is a prominent feature, because of its contrast with the rest of the image. So picking colors for a reduced bitmap isn't all that simple. I had to attack similar problems when writing some internal tools when we were developing Roger Rabbit. I strongly recommend you get yourself a book on image processing (something I should have done). _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ Leo L. Schwab -- The Guy in The Cape INET: well!ewhac@ucbvax.Berkeley.EDU \_ -_ Recumbent Bikes: UUCP: pacbell > !{well,unicom}!ewhac O----^o The Only Way To Fly. hplabs / (pronounced "AE-wack") "Work FOR? I don't work FOR anybody! I'm just having fun." -- The Doctor
jmdavis@ihlpm.ATT.COM (Davis) (04/28/89)
First, you may want to post this to comp.graphics also. There
they have human factors types and references to the SIGGRAPH
journals where just your type of palette compression could
have been discussed in the past.
Second, I wouldn't weigh BLUE as heavily as I would RED and
GREEN. BLUE is harder for humans to see. This would have drastic
changes in both your most popular color algorithm and your best
fit algorigthm. Think about it, I would say that color (RGB) (332)
should be lumped together with colors (333) and (331).
Third, I don't think .tech is the appro place for this (but I am
not sure, so I post here too). .tech is for technical Amiga stuff,
you have asked a technical graphics question, not dealing with amiga
system function calls, amiga system programming, etc.
--
----------------------------------------------------------------------------
Mike Davis ..!att!ihlpm!jmdavis
char*p="char*p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}raz@kilowatt.uucp (Raz- Berry) (04/28/89)
In article <11430@well.UUCP> ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes: )In article <33747@kilowatt.uucp> raz@kilowatt.uucp (Raz- Berry) writes: )) I need a basic flowchart )) on taking a 4096 color palette and converting it down to )) 256. Initially I was thinking that: )) [I take a first stab at a HAM conversion routine ... deleted] ) Permit me to poke a hole in this. ) [Leo, armed with a short sword, makes swiss cheese out of my first pass] )... However, that white line is a )prominent feature, because of its contrast with the rest of the image. So )picking colors for a reduced bitmap isn't all that simple. Yeah, I had similar thoughts. I recognized the problem, I was hoping some one could 'show me the way' to enlightened color mapping techniques. As it turns out, a fellow named Tony Kennedy sent me some very interesting conversion and dithering routines. Perhaps the version after the next release will include dithering routines as well as HAM capability. So if I include HAM conversion, you can all thank Tony. BTW: I have included Extra-Half-Bright support to iff2sun and I will be posting to Bob the new source soon. I am not too happy with the way 320x400 images look on a Sun color monitor though. There is a definate elongation effect because of the different aspect ratio between the two machines. So far the best results have been with 640 (or larger) x400 images 'rastrepl'ed once, to fit the Sun screen. I like the hires LION that comes with PixMate... looks pretty good on mono. ) I had to attack similar problems when writing some internal tools )when we were developing Roger Rabbit. I strongly recommend you get yourself )a book on image processing (something I should have done). Gee, I suppose sharing the RR code is out of the question huh? ;-) )_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ )Leo L. Schwab -- The Guy in The Cape INET: well!ewhac@ucbvax.Berkeley.EDU -- Steve -Raz- Berry Disclaimer: I didn't do nutin! UUCP: sun!kilowatt!raz ARPA: raz%kilowatt.EBay@sun.com "Fate, it protects little children, old women, and ships named Enterprize"
coy@ssc-vax.UUCP (Stephen B Coy) (04/28/89)
In article <11430@well.UUCP>, ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes: > In article <33747@kilowatt.uucp> raz@kilowatt.uucp (Raz- Berry) writes: > > I need a basic flowchart > > on taking a 4096 color palette and converting it down to > > 256. Initially I was thinking that: > > > > [algorithm deleted for brevity] > > Suppose I have a simple HAM picture. The left half of the screen is > various hues of purple, and the right half of the screen is various hues of > blue. Separating these two fields is a vertical line, one pixel wide, that > is solid white. > > Now, if you were to do a histogram on this image, you'd probably > find the most popular 256 entries were hues of purple and blue, and white > would be right at the bottom of the list. However, that white line is a > prominent feature, because of its contrast with the rest of the image. So But rememeber, he's starting with a 4096 color palette which means only 16 hues of pure blue. Even allowing for going slightly off color you'll probably end up with less than 50 shades each of blue and purple. This still leaves over 100 palette entries for various shades of white. When DBW_render first appeared I coded up the algrothm as proposed for displaying the images on an Apollo with a 256/16M palette. The images looked fine. For mapping the non-popular colors onto the 256 color palette I used a simple distance function in RGB space. Obviously not the best but good enough. Stephen Coy uw-beaver!ssc-vax!coy
raz@kilowatt.uucp (Raz- Berry) (04/29/89)
In article <3404@ihlpm.ATT.COM> jmdavis@ihlpm.ATT.COM (Davis) writes: >First, you may want to post this to comp.graphics also. There Yeah, I should have. I figured that there are a *LOT* of Amiga people who know of (or at least where to look for) methods to do this. >Second, I wouldn't weigh BLUE as heavily as I would RED and >GREEN. BLUE is harder for humans to see. This would have drastic Good to know. >Third, I don't think .tech is the appro place for this (but I am >not sure, so I post here too). .tech is for technical Amiga stuff, >you have asked a technical graphics question, not dealing with amiga >system function calls, amiga system programming, etc. Hmm, that sounds like comp.sys.amiga.tech.programming to me. This was a technical question on converting the Amiga palette down to one that can be used on a Sun. Iff2sun is a utility used by people who have Amiga's and want to display pictures they have on Sun machines. Lets' see, technical Amiga question about a utility used ONLY by people who have Amiga's. Maybe I should post to alt.sex. ;-) > Mike Davis ..!att!ihlpm!jmdavis -- Steve -Raz- Berry Disclaimer: I didn't do nutin! UUCP: sun!kilowatt!raz ARPA: raz%kilowatt.EBay@sun.com "Fate, it protects little children, old women, and ships named Enterprize"
doug@xdos.UUCP (Doug Merritt) (05/01/89)
In article <3404@ihlpm.ATT.COM> jmdavis@ihlpm.ATT.COM (Davis) writes: >Second, I wouldn't weigh BLUE as heavily as I would RED and >GREEN. BLUE is harder for humans to see. This amounts to gamma correction, doesn't it? Doug -- Doug Merritt Member, Crusaders for a Better Tomorrow {pyramid,apple}!xdos!doug Professional Wildeyed Visionary "Of course, I'm no rocket scientist" -- Randell Jesup, Capt. Boinger Corps
bdb@becker.UUCP (Bruce Becker) (05/07/89)
In article <254@xdos.UUCP> doug@xdos.UUCP (Doug Merritt) writes: |In article <3404@ihlpm.ATT.COM> jmdavis@ihlpm.ATT.COM (Davis) writes: |>Second, I wouldn't weigh BLUE as heavily as I would RED and |>GREEN. BLUE is harder for humans to see. | |This amounts to gamma correction, doesn't it? Nope. -- __ Bruce Becker Toronto, Ont. w \cc/ Internet: bdb@becker.UUCP, bruce@gpu.utcs.toronto.edu `/v/-e BitNet: BECKER@HUMBER.BITNET _< >_ "Where is Newton Minow now that we need him?" - T. S. Eliot
douglee@becker.UUCP (Doug Lee) (05/07/89)
In article <482@becker.UUCP> bdb@becker.UUCP (Bruce Becker) writes: >In article <254@xdos.UUCP> doug@xdos.UUCP (Doug Merritt) writes: >|In article <3404@ihlpm.ATT.COM> jmdavis@ihlpm.ATT.COM (Davis) writes: >|>Second, I wouldn't weigh BLUE as heavily as I would RED and >|>GREEN. BLUE is harder for humans to see. >| >|This amounts to gamma correction, doesn't it? > > Nope. I can't stand just a simple Nope without an explaination:-). Gamma correction is nonlinear amplification applied to the video signal's amplitude to compensate for the fact that television picture tubes are nonlinear EG: twice as much video level doesn't make the picture twice as bright. Correction for this is always applied in TV cameras (Commercial ones, I don't know about the cheap home ones). The ratio between R G and B signals when mixed to produce monochrome is something else entirely. The ratio is something like 11% Blue, 59% Green and the rest Red. These are not necessarily the CORRECT figures as I don't have them right here. If anyone really needs to know, I can look it up later. <<<Doug>>> > >-- > __ Bruce Becker Toronto, Ont. >w \cc/ Internet: bdb@becker.UUCP, bruce@gpu.utcs.toronto.edu > `/v/-e BitNet: BECKER@HUMBER.BITNET >_< >_ "Where is Newton Minow now that we need him?" - T. S. Eliot