A query in the same context

Indexed Color uses altogether only 256 colors or grays.
Each pixel byte points to a table with three entries RGB.

Handling layers requires color mixing in TrueColor – one byte (or two) for each channel RGB.

Theoreticall one could assign layers to an Indexed Color, but the results by mixing would be terrible, because they had to be rounded to the next AVAILABLE table color.

The practical solution: convert Indexed to TrueColor.
Apply any modification. Convert to Indexed, using a
new adapted table (automatically).

Best regards –Gernot Hoffmann

"Geetika" wrote:

Hi all

This in context to the same topic that was being discussed sometime before.
I am aware of the fact that i can not add layers to an indexed color file. But could anyone help me in understanding the reason behind it. I mean why cant an indexed color file possess multiple layers ??

It’s the math behind it. I think you have troubles understanding what "indexed" actually means. Think of a chinese restaurant. If the typical menu at your place looks as it looks here, you will soon know that your notorious wan tan soup and duck canton style ar numbers 6 and 42. It is sufficient to tell the waiter that you want the 6 and 42 as usual and you can be sure to get the right thing. However, if you go to the restaurant in the next town and order numbers 6 and 42 you may well get sweet sour soup and chop suey instead. With an indexed image it is the same thing. In one image the 6 points to teal and the 42 to dark yellow, in the next one the same numbers point to purple red and ice blue. You cannot do meangingful calculations on the indexes. Try to order nuber (6 + 42)/2 = 24 at your china restaurant. I am pretty sure you will get abalone or bami goreng but definitely not wan tan filled with duck canton style. But blending layers at 50 % opacity requires exactly this kind of math.

Peter