An individual can not be expected to map precisely to these averages and conditions. ANSI has developed recommendations based on the 1976 CIE Uniform Color Space. ISO9241, part 8, is still under development at this writing due to the difficulty of treating the subject analytically, yet with perceptual validity. The key issue addressed by ANSI is the excessive use of color for coding. Modem displays are capable of addressing a large number of points in color space, G .
G is the number of gray scale values.
It is important that application designers refrain from using more than nine levels and that the color separation between levels be large. A display with the addressability illustrated above can permit tuning of four to nine colors to the individual user. And, of course, realistic rendition of color images requires the use of many color points. Photochrominance criteria are an attempt to specify the equivalent contrast when both color and luminance differences are present. The recommended minima, however, are not mandatory.