|Baseline TIFF Tag BitsPerSample|
TIFF Tag Reference
TIFF Tag BitsPerSample
Number of bits per component.
Note that this field allows a different number of bits per component for each component corresponding to a pixel. For example, RGB color data could use a different number of bits per component for each of the three color planes. Most RGB files will have the same number of BitsPerSample for each component. Even in this case, the writer must write all three values.
LibTiff does not support different BitsPerSample values for different components.