Hi. As far as I understand, with L*a*b* colorspaces, a* and b* are real values with no simple bounding, but with useful values somewhere in [-128,128]. This is fine when the input is floating point values, but when dealing with octets, some sort of scaling is required. As far as I understand, lcms uses an hard-coded scaling to [-128,128[.
Now, if we have an image stream in a PDF file, with three 8-bit channels, we have a stream of octets. The colorspace of that stream can be defined by something like: /Lab << /WhitePoint [ 0.9642 1 0.82491 ] /Range [ -100 100 -100 100 ] >> The /Range argument tells us that the second and third octets, which stand for a* and b*, must be scaled so that 0 is -100 and 255 is +100; the range for L* is always [0, 100]. Some others PDF can have others ranges, [-128, 127] is quite common. With the [-128, 127] range, lcms can be used directly on the buffer of the stream, with a TYPE_Lab_8 type. But with others ranges, it seems necessary to do the intermediate conversion, which is quite a waste. Is there some way to tell lcms the ranges for a* and b* so it can do the conversion itself more efficiently? Regards, -- Nicolas George
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