Newsgroups: sci.engr.color From: jeff@wa1hco.mv.com (Jeff Millar) Subject: Re: linear RGB Date: Thu, 8 Feb 1996 02:47:04 GMT grape%/etc/HOSTNAME (Johan A. Grape) wrote: >Well - here's a question regarding color. >I'm writing an X application that does continuous color >contour plotting. Only thing is that I have no idea >what the correct equation is to "linearize" blending >of colors. >What I want to do is e.g. red -> yellow -> green (in RGB) >I first just used a linear ramp with 8 bit rep >of each colors. So that red has a negative slope and green >has a positive slope, but then I get a narrow strip of yellow >in the center and lots of green and red. >Any references on what the correct intensity equation >should be would be appreciated. Hope this is adequate >info. Check out the excellent description of color in the following web page. I think you will find that RGB space is mathematically linear. However you may not like the perception of the resulting colors. http://www.inforamp.net/~poynton/Poynton-colour.html jeff ============================================================================== From: hafner@suncog2.forwiss.tu-muenchen.de (Walter 'madhouse' Hafner) Newsgroups: sci.engr.color Subject: Re: colors ... colors! Date: 09 Feb 1996 10:46:08 GMT >>On 7 Feb 1996 10:53:05 GMT, ras@rd.bbc.co.uk (Richard Salmon) said: RS> Spicy Pasul (pjaffe@wam.umd.edu) wrote: RS> : RS> : I got the welcome and charter ... are there any textbooks on this RS> : subject I might consult? (color that is) RS> The Reproduction of Colour in Photography, Printing & Television RS> R.W.G.Hunt. Fountain Press. ISBN 0 86343 088 0 RS> Measuring Colour RS> R.W.G.Hunt. Ellis Horwood. ISBN 0-13-567686-X Very good indeed. But make sure you get the 2nd edition from 1995. RS> Color in Electronic Displays RS> Ed: Widdel and Post. Plenum Press. ISBN 0-306-44191-8 RS> Bob Hunt (I should say: Prof. Hunt) comes from Kodak, so is excellent on RS> Photo & Printing. For TV the following is better (but out of print): RS> Colour Science in Television and Display Systems RS> W.N.Sproson. Adam Hilger. ISBN 0-85274-413-7 Don't forget the "bible": Color Science: Concepts and Methods, Quantitative Data and Formulae 2nd Edition Günther Wyszecki, W.S. Stiles John Wiley & Sons, 1982 ISBN 0-471-02106-7 And I can recommend: Color Measurement - Theme and Variations, 2nd Edtition D.L. MacAdam Springer 1985 ISBN 0-387-15573-2 Oh - and for the video engineers out there (hello Alan, Charles :-) Video Demystified - A Handbook for the Digital Engineer Keith Jack Brooktree, 1993 ISBN 1-878707-09-4 Not much about color (except lots of info about color spacer used in broadcasting) but much infos about encoding standatrds (PAL/NTSC ...) -Walter -- Walter Hafner_____________________________ hafner@forwiss.tu-muenchen.de FORWISS Muenchen, FG Kognitive Systeme, Raum O-134, Tel: 089/48095-220 R)etry, A)bort F)reebsd ? *CLICK* ============================================================================== From: wmdawes@colorpro.com (Bill Dawes) Newsgroups: sci.engr.color,sci.physics,sci.chem Subject: Re: Chromaticity diagrams, anyone? Date: 11 Feb 1996 23:14:44 GMT I enjoyed Jonathan Hardis' answers very much. Many of us know Jonathan, frequent poster to sci.engr.lighting. He was a lot help to me in forming this group. >In article <4fbldt$b3o@ousrvr3.oulu.fi>, kempmp@sun3.oulu.fi (Petri Pihko) >wrote: > >> Are there any programs available that could reproduce the >> chromaticity diagram - that is, create a representation of >> it _in full colour_, for instance, as a .rgb, .tiff or .gif >> image? What other tools for manipulating and using the diagram >> are available? > >> I would definitely like to know if there is any ready method to do >> it right, by calculating every pixel from the rules. My ISP lost the original message... but all fans of the shoe shaped xyY Chromaticity diagram should enjoy the CVD.ZIP Interactive Color Vision Demonstration at http://www.uni-mannheim.de/unima/fakul/psycho/irtel/cvd.htm This is Dr. Hans Irtel's program for PC, VGA, and mouse. Fascinating and clever program lets you vary the color, using the CIE diagram, to study dozens of psychological experimental diagrams. I loved it! Bill Dawes wmdawes@colorpro.com ============================================================================== From: alanr@rd.bbc.co.uk (Alan Roberts) Newsgroups: sci.engr.color,sci.physics,sci.chem Subject: Re: Chromaticity diagrams, anyone? Date: 12 Feb 1996 15:06:07 GMT Gaurav Sharma (gsharma@unity.ncsu.edu) wrote: : : The Chromaticity diagram can be readily drawn by using the : CIE color matching functions for obtaining the chormaticity coordinates : for monochromatic light stimuli (and geometry for closing and filling in) : sometime back I wrote a program that creates a TIFF version of the : chromaticity diagram. Since we got rid of the TIFF library functions that : the library used I don't have the program available but I have the : diagram itself. If that would be of interest to you I can mail you a : uuencoded copy. There's a slight problem here; the chromaticity coordinates of the spectrum locus are tabulated, not derived from the colour-matching functions (or, at least not by any easy relationship). They are tabulated in most of the approved books on colorimetry, but they are _defined_ for us all in a CIE document, Tech.15 (my copy is dated 1971, but facts like these don't change much). For xy values, you need Table 2.1 for 1nm data at 2 degrees, Table 2.2 for 1nm data at 10 degrees, Table 2.3.1 for 5nm data at 2 degrees, Table 2.3.2 for 5nm data at 10 degrees. The 2 degree tables date from 1931 and relate to 2 degree visual areas, the 10 degere tables date from 1964. TV (and any other off-screen viewing) calculations should use the 2 degree sets. Tables 2.3.3 and 2.3.4 give 5nm data in 1960 uv values (2/10 degree), Tables 2.4 and 2.5 give 5nm data in CIE rgb values (2/10 degree). Don't confuse CIE rgb with TV rgb, the primaries are very different. -- ******* Alan Roberts ******* BBC Research & Development Department ******* * My views, not necessarily Auntie's, but they might be, you never know. * ************************************************************************** ============================================================================== From: wmdawes@colorpro.com (Bill Dawes) Newsgroups: sci.engr.color Subject: Re: Munsell soils? Date: 13 Feb 1996 04:05:16 GMT In article <4fngk3$n4j@whitbeck.ncl.ac.uk>, bram@myhost.subdomain.domain says... > >Bill Dawes (wmdawes@colorpro.com) wrote: >: tejas@infi.net (Ted Samsel) wrote: > >: If you find any RGB or xyY values for this, or any of the Munsell >: or Gardner color scales, > >This does not really make sense as you only have half of the puzzle. >Munsell and Gardner scales are standard reflectances that alter >when the illuminant changes. You could publish the xyY values under >a given illuminant e.g. D65 or CIE illum C but that probably is not >too useful. I suspect that soil samples as viewed in daylight would be fairly useful, since it's often found out of doors. >The whole spectra of the Munsell patches are at >http://www.lut.fi/~haanpalo/lutcs_database.html >and can be used to convolve with an illuminant spectrum so that you >can then use the CIE colour matching functions to create the xyY >value for a patch under a illuminant. Yes, thank you, I know this, and know of the fine data collection from our Finnish colleague. The missing puzzle piece is the Munsell names of the series in the soil sample set. I wonder what the original poster was up to in his short question, what he wanted to do with the soil sample color data? There's more than Munsell spectral data at Jouni Haanpalo's site: he also has forest and earth colors. And there's also the US Geodetic Survey database of mineral spectra. at ftp://speclab.cr.usgs.gov/pub/spectral.library. >(oh well, back to my thesis on Colour Constancy in Simple >and Complex Scenes) David Bramwell Good luck on your thesis! Have you seen Johan Lammens diss on the Web? Wish more PhD's would publish on the Web! Think about it... The thesis is "A Computational Model of Color Perception and Color Naming, at http://www.cs.buffalo.edu/pub/colornaming/diss/diss.html -- Bill Dawes wmdawes@colorpro.com http://www.colorpro.com/~color/wmdawes 13020 Birchleaf Road - Chester, VA 23831 - 804-748-8639 ==============================================================================