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Changed color interpolation to occur in linear colorspace #4

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Changed color interpolation to occur in linear colorspace #4

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30 changes: 18 additions & 12 deletions src/color_grading_lut.shader
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,12 @@ vec3 get_interpolated_color(vec3 floorc, vec3 diff, float perc){
return floorc.rgb + diff.rgb * perc;
}

// Applies gamma correction to convert color from linear space to sRGB.
vec3 convert_srgb_to_linear(vec3 srgb_color){
float gamma = 2.2;
return pow(srgb_color.rgb, vec3(gamma));//<--
}

// Applies gamma correction to convert color from linear space to sRGB.
vec3 convert_linear_to_srgb(vec3 linear_color){
float gamma = 2.2;
Expand All @@ -34,12 +40,12 @@ vec3 convert_linear_to_srgb(vec3 linear_color){
// Gets LUT mapped color using trilinear interpolation.
vec4 get_lut_mapping_trilinear(vec4 old_color){
float lut_div = lut_size - 1.0;
// Get floor and ceil colors and diff from identity lut
// Get floor and ceil for srgb colors, convert to linear and diff between them
vec3 old_color_lut_base = lut_div * old_color.rgb;
vec3 old_color_floor_vec = floor(old_color_lut_base);
vec3 old_color_ceil_vec = ceil(old_color_lut_base);
vec3 old_color_diff = (old_color_floor_vec - old_color_ceil_vec)/lut_div;
vec3 old_color_percentages = get_interp_percent_color(old_color.rgb, old_color_floor_vec/lut_div, old_color_diff);
vec3 old_color_diff = convert_srgb_to_linear(old_color_floor_vec/lut_div) - convert_srgb_to_linear(old_color_ceil_vec/lut_div);
vec3 old_color_percentages = get_interp_percent_color(convert_srgb_to_linear(old_color.rgb), convert_srgb_to_linear(old_color_floor_vec/lut_div), old_color_diff);
// Get the surrounding 8 samples positions
vec3 lut_color_fff_vec = vec3(old_color_floor_vec.r, old_color_floor_vec.g, old_color_floor_vec.b);
vec3 lut_color_ffc_vec = vec3(old_color_floor_vec.r, old_color_floor_vec.g, old_color_ceil_vec.b);
Expand All @@ -58,14 +64,14 @@ vec4 get_lut_mapping_trilinear(vec4 old_color){
ivec2 lut_color_ccf_pos = ivec2(int(lut_size*lut_color_ccf_vec.b + lut_color_ccf_vec.r), int(lut_color_ccf_vec.g));
ivec2 lut_color_ccc_pos = ivec2(int(lut_size*lut_color_ccc_vec.b + lut_color_ccc_vec.r), int(lut_color_ccc_vec.g));
// Get gamma corrected color from LUT.
vec3 lut_color_fff = convert_linear_to_srgb(texelFetch(lut, lut_color_fff_pos, 0).rgb);
vec3 lut_color_ffc = convert_linear_to_srgb(texelFetch(lut, lut_color_ffc_pos, 0).rgb);
vec3 lut_color_fcf = convert_linear_to_srgb(texelFetch(lut, lut_color_fcf_pos, 0).rgb);
vec3 lut_color_fcc = convert_linear_to_srgb(texelFetch(lut, lut_color_fcc_pos, 0).rgb);
vec3 lut_color_cff = convert_linear_to_srgb(texelFetch(lut, lut_color_cff_pos, 0).rgb);
vec3 lut_color_cfc = convert_linear_to_srgb(texelFetch(lut, lut_color_cfc_pos, 0).rgb);
vec3 lut_color_ccf = convert_linear_to_srgb(texelFetch(lut, lut_color_ccf_pos, 0).rgb);
vec3 lut_color_ccc = convert_linear_to_srgb(texelFetch(lut, lut_color_ccc_pos, 0).rgb);
vec3 lut_color_fff = texelFetch(lut, lut_color_fff_pos, 0).rgb;
vec3 lut_color_ffc = texelFetch(lut, lut_color_ffc_pos, 0).rgb;
vec3 lut_color_fcf = texelFetch(lut, lut_color_fcf_pos, 0).rgb;
vec3 lut_color_fcc = texelFetch(lut, lut_color_fcc_pos, 0).rgb;
vec3 lut_color_cff = texelFetch(lut, lut_color_cff_pos, 0).rgb;
vec3 lut_color_cfc = texelFetch(lut, lut_color_cfc_pos, 0).rgb;
vec3 lut_color_ccf = texelFetch(lut, lut_color_ccf_pos, 0).rgb;
vec3 lut_color_ccc = texelFetch(lut, lut_color_ccc_pos, 0).rgb;
// Calculate first level interpolations.
vec3 lut_color_iff = get_interpolated_color(lut_color_fff, lut_color_fff - lut_color_cff , old_color_percentages.r);
vec3 lut_color_ifc = get_interpolated_color(lut_color_ffc, lut_color_ffc - lut_color_cfc, old_color_percentages.r);
Expand All @@ -77,7 +83,7 @@ vec4 get_lut_mapping_trilinear(vec4 old_color){
// Calculate third and final interpolation.
vec3 lut_color_iii = get_interpolated_color(lut_color_iif, lut_color_iif - lut_color_iic, old_color_percentages.b);
// Get final color with original alpha.
vec4 final_color = vec4(lut_color_iii, old_color.a);
vec4 final_color = vec4(convert_linear_to_srgb(lut_color_iii), old_color.a);
return final_color;
}

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