cn@allgfx.agi.oz (Con Neri) (02/08/90)
Does anybody know of the proper conversions to produce 1) YMCK color images from RGB images. 2) RGB images from YMCK images. Any help with the above will be much appreciated. Please e-mail your reply or post into this newsgroup, I will summarise if there are enough replies. thanks in advance CON NERI All Graphic R+D e-mail: cn@allgfx.agi.oz.au 73 Whiteman ST tele: +61-3-6966401 South Melbourne tele: +61-3-6464333 Vic 3205 tele: +61-3-6906788 AUSTRALIA
piety@hplred.HP.COM (Bob Piety) (02/09/90)
Given components in the 0..1 range, C = 1 - R M = 1 - G Y = 1 - B K = .59R + .30G + .11B = Luminance
darcy@druid.uucp (D'Arcy J.M. Cain) (02/09/90)
In article <1990Feb7.220805.27260@allgfx.agi.oz> cn@allgfx.agi.oz (Con Neri) writes: >Does anybody know of the proper conversions to produce > 1) YMCK color images from RGB images. > 2) RGB images from YMCK images. > >Any help with the above will be much appreciated. Please e-mail your reply or >post into this newsgroup, I will summarise if there are enough replies. > given that the colours range from 0 to 255: Cyan is 255 - red Magenta is 255 - green Yellow is 255 - blue This will give the primary subtractive colours. To include black, subtract the lowest of the CMY values from each (making at least one of them 0) and the subtracted value is the black component. The reverse should be obvious. -- D'Arcy J.M. Cain (darcy@druid) | Thank goodness we don't get all D'Arcy Cain Consulting | the government we pay for. West Hill, Ontario, Canada | (416) 281-6094 |
darcy@druid.uucp (D'Arcy J.M. Cain) (02/10/90)
In article <260002@hplred.HP.COM> piety@hplred.HP.COM (Bob Piety) writes: >Given components in the 0..1 range, > >C = 1 - R >M = 1 - G >Y = 1 - B >K = .59R + .30G + .11B = Luminance I previously posted a different algorithm for this problem and it appears now that I may have been wrong (not a first for me :-) ). My algorithm basically subtracted an equal amount from each of the resulting C, M and Y values making this subtracted amount the black component. I recognize the RGB->Greyscale calculation in the above statement and I can understand that the different components might have differing weights in the calculation but doesn't the black component, at least to some extent, have to be adjusted by reducing the CMY components. Is the above generally accepted. None of the texts I have seen really details this algorithm. Thanks for your help. -- D'Arcy J.M. Cain (darcy@druid) | Thank goodness we don't get all D'Arcy Cain Consulting | the government we pay for. West Hill, Ontario, Canada | (416) 281-6094 |
buck@drax.gsfc.nasa.gov (Loren (Buck) Buchanan) (02/12/90)
In article <1990Feb10.151544.19088@druid.uucp> darcy@druid.UUCP (D'Arcy J.M. Cain) writes: >In article <260002@hplred.HP.COM> piety@hplred.HP.COM (Bob Piety) writes: >>Given components in the 0..1 range, >> >>C = 1 - R >>M = 1 - G >>Y = 1 - B >>K = .59R + .30G + .11B = Luminance > >Is the above generally accepted. None of >the texts I have seen really details this algorithm. This is actually a very complicated problem that is not totally solved. I imagine that several PhD's can be earned researching this topic. It really boils down to what are the CMYK values going to be used for. The conversion to CMY is correct. The problem with K is that if you use these four values for percentages of ink to be put to paper your image will be much to dark. The computation of K is typically on the order of: 1. Set K to the smallest value of CMY 2. Subtract K from C, M, and Y The problem with the above computation is that it does not take into account the various interactions of the four different inks, the paper it is applied to, and the printing process used. These interactions are usually non-linear. The thing to do is find a printer who can give you the values you need (for a particular paper/ink set combination). Welcome to the confusing world of printing. (I am not involved in the printing industry, but I have had discussions with an expert in the field) B Cing U Buck Loren "Buck" Buchanan | internet: buck@drax.gsfc.nasa.gov | standard disclaimer CSC, 1100 West St. | uucp: ...!ames!dftsrv!drax!buck | "By the horns of a Laurel, MD 20707 | phonenet: (301) 497-2531 or 9898 | sky demon..."