Information AboutSrgb |
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is shown in the center.]] sRGB color space, or '''standard RGB''' (Red Green Blue), is an RGB Color Space created cooperatively by Hewlett-Packard and Microsoft Corporation . It has been endorsed by the W3C , Exif , Intel , Pantone , Corel , and many other industry players. It is also well accepted by Open Source software such as the GIMP , and is used in proprietary and open Graphics File Format s such as SVG . sRGB defines the red, green, and blue Primaries as colors where one of the three channels is at the maximum value and the other two are at zero. In CIE Xy Chromaticity Coordinates red is at 0.3300 , green at 0.6000 and blue is at 0.0600 and the White Point is the D65 white point at [0.3127,0.3290]. sRGB has been criticised for poor placement of these primary colors. If you restrict the indexes to the 0 to 1 range you are unable to address outside the Gamut (the triangle produced by them), which is well inside the set of visible colors to a human. sRGB also defines a non-linear transformation between the intensity of these primaries and the actual number stored. The curve is similar to the gamma response of a CRT display. It is more important to replicate this curve than the primaries to get correct display of an sRGB image. This non-linear conversion means that sRGB is a reasonably efficient use of the values in an integer-based image file to display human-discernable light levels. It is important to realize that sRGB was designed to match what current (in 1996 ) CRT monitors do. Vast amounts of software, both professional and personal computer software, assumed an 8-bit image file placed unchanged into an 8-bit/channel display buffer will display with these colors and intensities. Modern non-CRT hardware, such as LCD screens, Digital Cameras , and printers, although they don't naturally produce an sRGB curve, have been built with compensating circuitry or software so that in the end they also obey this standard, for compatibility reasons (this is somewhat less true for high-end professional equipment). For this reason you can assume (in the absence of embedded profiles or any other information) that any 8-bit image file, and any 8-bit image API or device interface, is in the sRGB color space. There is a debate over color spaces that may (to outsiders) be surprising in its forcefulness. sRGB is frequently criticised by publishing professionals because of its narrow color gamut, which means that some colors that are visible, even some colors that can be reproduced in CMYK cannot be represented by sRGB. See RGB Color Space for the view that Adobe RGB is a preferred standard. SPECIFICATION OF THE TRANSFORMATION The forward transformation Calculation of sRGB tristimulus values from CIE xy chromaticity coordinates : Let C be R, G, or B:
The reverse transformation : where : for : otherwise THEORY OF THE TRANSFORMATION The non linear part of the transformation was designed to approximate a Gamma of about 2.2, but without having a zero slope at K=0, which can cause numerical problems. This is approximately true for the sRGB transformation. The condition that g(K) match at some is: : where the standard value of which was used above, yields =0.04045... and this is the transformation used. If we impose the condition that the slope match as well then we must have: : We now have two equations. If we take the two unknowns to be and then we can solve to give =0.03928... and =12.9232.... These values are sometimes used for the sRGB specification, although they are not standard. EXTERNAL LINKS
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