Hello,

I am trying to implement somekind of color correction.

I already implemented 1D LUT color correction, which is really easy to code and palette is easy to make.

Now, I would like to use 3D LUT, so i am able to control more color tranformations.

It's based on this http://udn.epicgames.com/Three/ColorGrading.html

I managed to use their standard palette, but problem is, i can't use hardware filtering as pixel is affected by another 16x16 table on left ( and right side ).

It's should be easy to do it with 3D texture, but how can i generate such a texture ? For me, easiest way is just use 2D texture like on the website i sent.

Do you have any ideas ? some tricks ?

Thank you very much.

About bleeding, it's caused by anisotropic sampler. If i use point sampler, it's working fine, but it only uses 1024 colours.

I also tried interpolated colour between two samples .. and i had bad results .. perhaps, i just did something wrong. It worked on my paper hehe.

Hello again :)

I think, i solved my problem. I just made a help function for converting from 2D UV to 3D UVW and back, and it helped me :)

This is my code, it's ComputeShader as I am doing mostly only CS, it's faster then vertex shader+pixel shader ( rendering quadscreen, etc ... ).

Texture2D<float4>   backbuffer             : register(t0);
RWTexture2D<float4> backbufferOut          : register(u0);
Texture2D<float4>   palette                : register(t1);

struct CSInput
{
   uint3 groupID  : SV_GroupID;
   uint3 threadID : SV_DispatchThreadID;
};


uint3 To3D( uint2 uv )
{
    uint blue = floor( uv.x / 16.0 );
    uint red  = uv.x - blue*16;
    uint green= uv.y;
    return uint3(red,green,blue);
}

uint2 To2D( uint3 uvw )
{
    uint v = uvw.y;
    uint u = uvw.z*16+uvw.x;
    return uint2(u,v);
}


[numthreads(16, 16, 1)]
void main( CSInput input )
{		
	float4 oldColor      = backbuffer.Load(uint3(input.threadID.xy,0));
    uint3  uColor        = oldColor.xyz*255;

    uint3  uvw_low       = floor( uColor/16.0);
    uint3  uvw_high      = ceil(  uColor/16.0);
    float3 uvw_avg       = uColor/16.0;

    float  xpercent = 0.0; float ypercent = 0.0; float zpercent = 0.0;
    if( uvw_high.x < 16) {if(uvw_high.x-uvw_low.x > 0) xpercent = 1.0-(uvw_high.x-uvw_avg.x); } else uvw_high.x=15;
    if( uvw_high.y < 16) {if(uvw_high.y-uvw_low.y > 0) ypercent = 1.0-(uvw_high.y-uvw_avg.y); } else uvw_high.y=15;
    if( uvw_high.z < 16) {if(uvw_high.z-uvw_low.z > 0) zpercent = 1.0-(uvw_high.z-uvw_avg.z); } else uvw_high.z=15;

    float4 color1         = palette.Load( uint3( To2D(uvw_low),0 ) );    
    float4 color2         = palette.Load( uint3( To2D(uvw_high),0 ) );
    float4 color3         = float4(0,0,0,1);

    color3.x = lerp( color1.x, color2.x, xpercent ); 
    color3.y = lerp( color1.y, color2.y, ypercent );
    color3.z = lerp( color1.z, color2.z, zpercent );   

	backbufferOut[input.threadID.xy] = color3;
}

if anyone has any idea, how to optimalize it (if it's possible ), i will be happy. Thanks

UV.rg = (UV.rg * 15.0f/16.0f) + (0.5f/16.0f);
You may not need the (0.5f/16.0f) at the end depending on whether you need the half texel offset.

Hi Hodgman,

i did not know about halfpixel for just sampling a texture. I know it only for dx9 quad screen rendering.

My case is a bit different here as I am using LOAD function, where input is UINT3. Not sure, if it still needs half pixel for float uv.

Styves: Thanks for ideas, i will check it. I will try to think about IF conditions, there are here to avoid reading from different 16x16 block.