Pixel Corruption From Neighboring Pixels with gl_FragCoord

[Rennie Johnson]

I'm trying to create a color filter array demosaicing fragment shader for raw capture from a color camera with color bayer filter. In order to properly decode the image, I require acces to clean neighboring texels without any averaging from neighboring texels. Since I'm not using TEXTURE_RECTANGLE textures, I'm a little nervous. I also have to know the exact x/y offset of the main pixel in the shader.

Here is a partial simple shader that implements the RGB values from a red pixel of the color bayer filter array:

[SIZE=2] #extension GL_EXT_gpu_shader4 : enable [SIZE=2][COLOR=#008000]//Required For Integer Modulus Operation (%)[/COLOR][/SIZE]
 
uniform sampler2D BayerCaptureSampler;
uniform [/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] captureImageWidth;
uniform [/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] captureImageHeight;
 
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]void[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#000000] main([/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]void[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#000000])[/COLOR]
{
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] step_w;
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] step_h;
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] fragOffsetFloatX;
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] fragOffsetFloatY
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]int[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] fragOffsetIntX;
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]int[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] fragOffsetIntY;
vec2 redOffset[4];
vec2 greenOffset[4];
vec2 blueOffset[4];
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]int[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] evenOddX;
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]int[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] evenOddY;
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]float[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] Sum;[/SIZE][SIZE=2]
 
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Example: ASSUME ORIGINAL SOURCE BUFFER OF 2048 x 1536
 
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Calculate Single Texel Normalized Offset From Original capture buffer resolution
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]step_w = 1.0/captureImageWidth;           [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Should return 1.0/2048.0 = 0.00048828125
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]step_h = 1.0/captureImageHeigh;            [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Should return 1.0/1536.0 = 0.00065104166
 
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Retrieve the Current Texel Offset (In Host Buffer Integer Coordinates From Corner (0,0)
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]fragOffsetIntX = gl_FragCoord.x;             [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Should Return Integer Value 0 to 2047
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]fragOffsetIntY = gl_FragCoord.y;             [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Should Return Integer Value 0 to 1535
 
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Determine if this is an even or odd pixel on horizontal and vertical offsets from bottom right corner texel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]evenOddX = fragOffsetIntX%2;               [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Should Return 0 for even, or 1 for odd
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]evenOddY = fagOffsetIntY%2;                [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Should Return 0 for even, or 1 for odd
 
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//*************************Sample Code For A Red Pixel Decocing******************//
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]if[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2](evenOddX==0) [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Width Offset = Even Texel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]{
[/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]if[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] {evenOddY==0) [/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Height Offset = Even Texel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]{
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Retrieve Red Texel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]glFragColor.r = texture2D(BayerCaptureSampler,vec(gl_TextCoord[0].st)).r;
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Calculate Green Pixel Offsets
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//THESE NEED TO BE IDENTICAL PIXEL VALUE FROM THE ORIGINAL BUFFER THAT WAS LOADED INTO
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//TEXTURE WIHTOUT ANY MIXTURE OR AVERAGING OF PIXELS ONCE INSIDE THE TEXTURE
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] greenOffset[0] = vec2(step_w,step_h);
  greenOffset[1] = vec2(0.0,step_h);
  greenOffset[2] = vec2(-step_w,0.0);
  greenOffset[3] = vec2(0.0,-step_h);
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Retrieve and Average Neighboring Green Pixels
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] sum = 0.0;
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + greenOffset[0];
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + greenOffset[1];
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + greenOffset[2];
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + greenOffset[3];
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Assign Final Calculated Green Texel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]glFragColor.g = sum/4.0;
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Calculate Blue Pixel Offsets
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//THESE NEED TO BE IDENTICAL PIXEL VALUE AS DESCRIBED ABOVE
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] greenOffset[0] = vec2(step_w,step_h);
  greenOffset[1] = vec2(-step_w,step_h);
  greenOffset[2] = vec2(step_w,-step_h);
  greenOffset[3] = vec2(-step_w,-step_h);
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Retrieve and Average Neighboring Blue Pixels
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] sum = 0.0;
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + blueOffset[0];
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + blueOffset[1];
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + blueOffset[2];
  sum += texture2D(BayerCaptureSampler,vec2(gl_TexCoord[0].st + blueOffset[3];
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Assign Final Calculated Blue Texel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]glFragColor.b = sum/4.0;
   }
}
[/SIZE][SIZE=2][COLOR=#008000][SIZE=2][COLOR=#008000]//Assign 1 to Alpha Channel
[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]glFragColor.a = 1.0
}
[/SIZE]

My questions are:

1) How do I implement the layout qualifier "pixel_center_integer" with this version of OpenGL? I need the offsets to be the actual integer values, not with 0.5 offsets.

2) Will my greenOffset[] and blueOffset[] texel offsets return me the original buffer pixels without any sub-pixel neighbor averaging? The color demosaicing will not work if the pixel values are in any way mixed.


Thanks for your help!