Hi there, Is it possible to implement "palettes" for rendering a greyscale image in with any set of colours you want using pixel shaders? I have a texture map that basically consists of luminosity data and I want to define various user-selectable palettes to view the dataset with. I figured if I just were able to upload a palette texture, upload the luminosity data and fire off a pixel shader program, I might be able to do this. But how? I''m new to pixel shaders. Any hints would be much appreciated.

Right, so you''re talking about a colour scale re-mapping rather than a traditional indexed colour palette. I hope so at least, as it makes it a lot easier

All you need to do is create a 1d texture with the colours you want given the luminance values. Basically, use the texture u coordinate as the luminance and draw the texture given that.

Now use this pixel shader:

tex t0
texreg2gb t1, t0
mov r0, t1

This reads from sampler stage 0 (which you set to be your luminance texture), then passes the green and blue channels as the u and v coordinates for a look up in sampler stage 1 (which you set to be your ''palette'').

If you''re using, say, an A8 luminance texture instead, then use the texreg2ar instruction as that maps alpha to u and red to v.

btw, don''t worry about what is mapped to v as you''re ignoring that anyway (you''ve got a 1d texture).

NB. If you meant true indexed palettes then it''s harder as you need to emulate bilinear filtering manually using 4 displaced samples.

HTH

Matt Halpin

Hey I got that one already - except I''m using ps11 (GeForce 3) so I''m using texreg2ar t1, t0. Basically, my luminance data is convieniently 16 bit anyway. I bind my 2d palette texture to t1 and off I go Works like a dream. So impressive this ps stuff (this is my first go at ps).

tex t0

texreg2ar t1, t0
mov r0, t1