RE: [Algorithms] Colour reduction code

[Killpack, C. <Ch...@ea...>]

We have a palettiser for our PSX2 game that uses VQ to generate an 8-bit
palette of 32-bit entries. I'm not sure which exact alg it uses. Maybe it's
homebrew. *shrugs*

For the next project I want to provide a Photoshop plug-in for artists which
will allow them to preview the results of our palettiser allowing them to
author their textures to produce the best quality output at convert time.

> -----Original Message-----
> From: Jason Dorie [mailto:jas...@bl...]
> Sent: Wednesday, July 11, 2001 12:21 PM
> To: gda...@li...
> Subject: RE: [Algorithms] Colour reduction code
> 
> 
> 
>   I could be wrong, but I don't believe that PhotoShop's palettized
> (indexed) images can contain alpha.  The only thing you could 
> do is quantize
> at export time and save directly to a file.  You're better 
> off leaving all
> the art as 32 bit, and doing the 32->8 conversion during the 
> build process.
> 
> Jason Dorie
> BlackBoxGames
> 
> 
> 
> -----Original Message-----
> From: gda...@li...
> [mailto:gda...@li...]On Behalf Of
> Michael Grayford
> Sent: Wednesday, July 11, 2001 12:06 PM
> To: gda...@li...
> Subject: RE: [Algorithms] Colour reduction code
> 
> 
> I don't suppose there is a photoshop plug-in version of this?
> 
> -----Original Message-----
> From: gda...@li...
> [mailto:gda...@li...]On 
> Behalf Of Jason
> Dorie
> Sent: Wednesday, July 11, 2001 11:35 AM
> To: gda...@li...
> Subject: RE: [Algorithms] Colour reduction code
> 
> 
> 
> If you want it in code, go here...
> 
> http://www.nucleus.com/~dorie/dxtctest/
> 
> ...and download the ImageLib.zip file on the page.  Among the 
> code in here
> is a variance-based median-cut style color reducer.  It 
> reduces full 32 bit
> data to produce a palette of as many colors as you ask for, 
> up to a maximum
> of 256 colors.  (The max can be easily modified)
> 
>   There is also an algorithm called Lloyd which is used in a 
> lot of vector
> quantization applications, which is exactly what palettizing 
> is.  Lloyd is
> slower, but more accurate than median cut.  The Variance-Cut method is
> working very well for our multiple consoles, with or without alpha.
> 
>   When thinking about it, don't try to visualize the space - 
> Just realize
> that the color componant values are related, and are along 
> multiple axis in
> an n-dimensional space, whether that's 1D (Grayscale), 2D (Grayscale +
> Alpha?), 3D (RGB), 4D (RGBA), 12D (4 x RGB), or 16D (4 x 
> RGBA).  I've used
> the exact same code to do image compression for the DreamCast 
> which uses 2x2
> pixel blocks which must be palettized, hence 12D & 16D.  
> Works like a hot
> damn.
> 
> Jason Dorie
> BlackBoxGames
> 
> 
> 
> -----Original Message-----
> From: gda...@li...
> [mailto:gda...@li...]On Behalf Of
> Stuart Capewell
> Sent: Wednesday, July 11, 2001 9:58 AM
> To: gda...@li...
> Subject: [Algorithms] Colour reduction code
> 
> 
> Hi,
> 
> we've got an octtree colour reduction algorithm to convert 
> 24-bit source
> textures to 8-bit palettised versions. It's working fine, but now our
> artists have presented us with 32bit textures including alpha 
> information.
> 
> Visualising that extra dimension and extending the algorithm 
> is proving
> tricky. Anyone know of a sensible approach? Most of our ideas 
> only seem to
> work for certain textures. Others with wider colour ranges 
> and/or different
> amounts of alpha come out looking pretty horrid.
> 
> My other solution was to get the artists to author the 
> textures in 8-bit
> with 32-bit palette entries to preserve the alpha component, 
> but they assure
> me they can't do this. Anyone know of a package that will do this?
> 
> 
> Stuart.
> 
> 
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