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Re: Inverse palette conversion algorithm... [message #2304 is a reply to message #2301]

Fri, 07 April 2006 11:16

mirek is currently offline

mirek
Messages: 14265
Registered: November 2005

Ultimate Member

What a nice trick, I did not knew this one! Thanks!

As for the purpose of the code: You have truecolor raster image and you have some existing palette. You want to convert truecolor to palette (indexed).

Now in theory, you should for each color of image find closest color - by equaction (r1 - r2)^2 + (g1 - g2)^2 + (b1 - b2)^2 (where ^2 is not xor but square).

Of course, performing this calculation for each pixel would be too slow, therefore standard approach reduces original pixel depth (to 64K colors here) and provides "inverse transformation cube" - a table that can be used to perform quick lookup of palette index for each possible color.

This algorithm builds such cube. "Brute force approach" is to go through all cells of cube and find closest color from palette for it. Above implementation is almost 20x faster in the average case...

Mirek

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[Message index]

		Inverse palette conversion algorithm... By: mirek on Wed, 05 April 2006 10:11
		Re: Inverse palette conversion algorithm... By: mr_ped on Fri, 07 April 2006 10:05
		Re: Inverse palette conversion algorithm... By: mirek on Fri, 07 April 2006 11:16
		Re: Inverse palette conversion algorithm... By: mr_ped on Fri, 07 April 2006 13:23
		Re: Inverse palette conversion algorithm... By: mirek on Fri, 07 April 2006 13:34
		Re: Inverse palette conversion algorithm... By: mr_ped on Fri, 07 April 2006 13:16
		Re: Inverse palette conversion algorithm... By: mirek on Fri, 07 April 2006 13:33
		Re: Inverse palette conversion algorithm... By: mr_ped on Fri, 07 April 2006 17:30
		Re: Inverse palette conversion algorithm... By: mr_ped on Fri, 07 April 2006 17:46
		Re: Inverse palette conversion algorithm... By: mirek on Sat, 08 April 2006 14:00
		Re: Inverse palette conversion algorithm... By: mr_ped on Mon, 10 April 2006 17:58
		Re: Inverse palette conversion algorithm... By: mr_ped on Sun, 21 May 2006 15:40
		Re: Inverse palette conversion algorithm... By: mr_ped on Sun, 21 May 2006 15:46
		Re: Inverse palette conversion algorithm... By: mirek on Sun, 21 May 2006 16:01

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