In a message dated 3/14/00 5:15:06 AM Eastern Standard Time,
[EMAIL PROTECTED] writes:
<< >Couldn't this be optimized by computing the squares for each color
>table entry as it is set into the table?
I don't think so. Well, anyway not much. To compute distance, you have to
square the difference. (a-b)^2 = a^2 - 2ab - b^2. So, even if you had a^2
precomputed you'd still have to do a bunch of multiplications.
Also, in the normal course of using the OS, we don't actually do
WinRGBToIndex very often. If you have an app that does it more frequently
or has custom needs, you're probably better of computing the indexes once
and caching them.
Beyond that.. well, there's API to get the current palette, so you could
always implement your own (better/faster) RGB to index routine!
>>
I would think that you would be able to use a table that holds the values for
the whole distance equation. Since range for a and b are both [0..255], the
range for (a-b) is -255 to +255 and you can make a 512 element table to hold
the values.
-Pete
PS: Shouldn't the mentioned equation be (a-b)^2 = a^2 - 2ab + b^2?
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