Digital Light & Color

I tried to count colors in an image and when the process reached about the middle of the progress bar, it virtually stopped. I cancelled it but it took another several minutes to free the PC for another work. Finally it displayed an intermediate number of about 6 milions colors.

The Cancel button does not cancel the counting but rather stops or interrupts it instead, and after that delivers some intermediate number. In my opinion delivering any intermediate number does not make much sense if you want to know the number of colors in a picture.
I think that if it starts looking as a huge number of colors (tens of thousands and more) it would be good to have a chance to really cancel the process and immediatelly free the memory.

Just out of curiosity, can anybody tell what is about the highest number of colors in a picture which still have some practical usage to know?

Counting unique colors for 48-bit color images can take a very long time, especially for large images. I should probably just remove this feature.

Or perhaps just stop counting once some meaningful top limit for color is reached. Since the human eye is said to distinguish about 30 shades of gray, the limit of 256 colors seems to make sense to me. Besides, somebody might be interested to know the number of shades in their image.

After reaching the top limit a message like "The top limit of nnn colors was reached. Counting all colors in a picture can take a very long time." could pop up.
I am not sure if there any use to know that there are, for example, about as few as 2000 colors in a picture. But of course, others might think otherwise.

It can be used as a measure of posterization which does have some value. Maybe counting the number of unique 24-bit colors would be more useful since the eye can't really see the difference between 24-bit and 48-bit colors.