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November 1999
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1999.11.02 18:27 "Re: grayscale tiff", by Richard J Otter
Hello all, Since the topic of grayscale TIFF has come up, I'd like to get your opinion about the use of some infrequently used (?) tags to help define the grayscale data range. Many desktop scanners will produce grayscale image with a 12 bit range. BitsPerSample could be set to 12, but this implies that the data has to be packed. If we want to keep the data on byte boundaries, we could store it in a 16 bit field with BitsPerSample set to 16. We find that more apps will open a 16 bit image than a 12 bit packed image. The problem now is that we have lost the value of the original data range. The data range is necessary if the stored transmitance values are to be converted to optical Density values. Without other information, one would have to assume that the range of values is from 0 to 2^16. One could look at the actual values in the image, but this still does not give the range necessary to convert to Optical Density. So- does it seem reasonable to use the SMinSampleValue and SMaxSampleValue tags to state that the actual range is from 0 to 4096 ? By the way, we do give the creator of the image the option to store a direct transmitance to OD lookup table (GrayResponseCurve tag), but even fewer apps know how to use this information. Thanks, Richard Otter