2004.05.20 11:05 "[Tiff] Extra samples handling", by Mayank

Hi,

Please confirm if i am correct with the extra samples handling in TIFF images.

If TIFFTAG_EXTRASAMPLES has:

Type as 1(associated alpha): then the color values have to be taken as it is. also the number of extra channels will always be one only.

Type as 2(unassociated alpha): then all the color values have to be multiplied by the alpha channel value.

Question 1: Are multiple unassociated alpha channels possible? If yes, then how are the final color values calculated?

Type as 0(unspecified data): then the extra channels have to be simply ignored.

Question 2: Are combinations of Type 2 and Type 0 possible for a particular TIFF image? If yes, do we need to ignore the alpha channel/multilply the color values with the vaues of the color channel accordingly?

Thanks,
Mayank