X-bit labs

EPSON Perfection 3170/4180 PHOTO Scanners Review (page 6)

Category: Other

by Sergey Samarin

[ 10/21/2004 | 02:22 PM ]

Profiling and Gamut Ranges

This section is concerned with evaluating the error in the scanners’ interpretation of the colors of the original IT8.7/2 color target with the help of a color management system. In other words, we will know the coefficient of the color distortion introduced by the scanner into the image. Below there are gamut range diagrams for opaque (reflective) and transparent (emissive) originals.

The gamut range is outlined with a triangle in the diagrams. It is a projection on the plane and shows the scanner’s palette in the visible light spectrum. Since we know the coordinates of the vertexes of the triangles, we can calculate their areas to estimate the absolute values of the ranges.

For the comparison’s sake, I also offer the squares of the triangles for the standard sRGB and Wide Gamut RGB color spaces (the former is used with the majority of monitors, and the latter is the maximum area in the CIE La*b* space).

The next diagram is constructed by calculating the difference between the colors of the original color target and its scan. Note that Color Difference values above 5.0 are discernable by most people, i.e. evident for the “average” human eye. 

The closer to the X axis – the better

The diagram shows that the errors in color reproduction fall on the darkest sections of the color target, starting from the point GS17.