If you are questioning why the spectrum boundary is rounded and not triangular, the answer goes like this: When you transform the responses to single wavelengths of the cone cells (or equivalently, the X, Y and Z standard observer curves) into ratios (chromaticities) such as (x, y) or (u', v'), whenever one of the three input values goes to zero for a range of wavelengths, the chromaticity will vary along a straight line. That's the way the math works, as seen in the well-known property that the chromaticity of a mixture of two colors lies on the straight line connecting their chromaticities. In the region of longer wavelengths from red to yellow-green, this is the case in the eye because the short-wavelength "blue" cone response is essentially zero, and it is only the medium and long wavelength cone response ratios that are changing. However, the long and medium wave cone responses are quite broad, so in the green and blue-green portions of the spectrum, the ratios of all three responses are varying, and thus you see the locus of spectral chromaticity gradually changing direction in a curved path. It is equivalent to mixing variable ratios of three primaries. Camera systems with narrower spectral responses produce a spectral locus that is closer to a triangle, and in fact, many color films, in which the short, medium and long wavelength ("red," "green" and "blue") responses essentially do not overlap, have a triangular locus of recorded spectral chromaticity. You can see this is in a picture of a spectrum, which will be reproduced as wide bands of red, green, and blue, with only narrow or non-existent transition regions of orange and yellow between the red and green, and cyan between the green and blue. This was covered in my SMPTE paper on wide-gamut imaging. Wayne Bretl -----Original Message----- From: colorsync-users-bounces+waynebretl=cox.net@lists.apple.com [mailto:colorsync-users-bounces+waynebretl=cox.net@lists.apple.com] On Behalf Of Ricardo Decastro Sent: Wednesday, April 06, 2016 6:43 PM To: Colorsync-users@lists.apple.com Subject: CIELab colorspace Hey anyone know why the original CIELab color space is shaped like a 'horseshoe'? please help -- *Ricardo Decastro* *810 West Maude* *Arlington Heights IL 60004* *312.560.9511* sendricardo@gmail.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Colorsync-users mailing list (Colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/colorsync-users/waynebretl%40cox.net This email sent to waynebretl@cox.net