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Add scaler API for YCbCr range #156

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Merged
Themaister merged 1 commit into from
Oct 7, 2026
Merged

Add scaler API for YCbCr range #156

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33 changes: 27 additions & 6 deletions video/scaler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,12 @@ void VideoScaler::set_ycbcr_chroma_midpoint(float midpoint)
ycbcr_chroma_midpoint = midpoint;
}

void VideoScaler::set_ycbcr_range(VkSamplerYcbcrRange range, unsigned bit_depth)
{
ycbcr_range = range;
ycbcr_range_bit_depth = bit_depth;
}

void VideoScaler::rescale(CommandBuffer &cmd, const RescaleInfo &info)
{
if (!recognized_color_space(info.input_color_space) || !recognized_color_space(info.output_color_space))
Expand Down Expand Up @@ -349,20 +355,35 @@ void VideoScaler::rescale(CommandBuffer &cmd, const RescaleInfo &info)
};
auto *ubo = cmd.allocate_typed_constant_data<UBO>(0, 4, 1);

vec3 cr_row, y_row, cb_row;
if (info.output_color_space == VK_COLOR_SPACE_HDR10_ST2084_EXT)
{
ubo->gamma_space_transform[0] = vec4(0.5f, -0.459786f, -0.0402143f, ycbcr_chroma_midpoint);
ubo->gamma_space_transform[1] = vec4(0.2627f, 0.678f, 0.0593f, 0.0f);
ubo->gamma_space_transform[2] = vec4(-0.13963f, -0.36037f, 0.5f, ycbcr_chroma_midpoint);
cr_row = vec3(0.5f, -0.459786f, -0.0402143f);
y_row = vec3(0.2627f, 0.678f, 0.0593f);
cb_row = vec3(-0.13963f, -0.36037f, 0.5f);
}
else
{
// Everything else is standard BT.709.
ubo->gamma_space_transform[0] = vec4(0.5f, -0.454153f, -0.0458471f, ycbcr_chroma_midpoint);
ubo->gamma_space_transform[1] = vec4(0.2126f, 0.7152f, 0.0722f, 0.0f);
ubo->gamma_space_transform[2] = vec4(-0.114572f, -0.385428f, 0.5f, ycbcr_chroma_midpoint);
cr_row = vec3(0.5f, -0.454153f, -0.0458471f);
y_row = vec3(0.2126f, 0.7152f, 0.0722f);
cb_row = vec3(-0.114572f, -0.385428f, 0.5f);
}

float luma_scale = 1.0f, luma_offset = 0.0f, chroma_scale = 1.0f;
if (ycbcr_range == VK_SAMPLER_YCBCR_RANGE_ITU_NARROW)
{
// H.273 narrow range: 16..235 luma and 16..240 chroma at 8 bits, scaled up for higher bit depths.
float code_unit = float(1u << (ycbcr_range_bit_depth - 8u)) / float((1u << ycbcr_range_bit_depth) - 1u);
luma_scale = 219.0f * code_unit;
luma_offset = 16.0f * code_unit;
chroma_scale = 224.0f * code_unit;
}

ubo->gamma_space_transform[0] = vec4(cr_row * chroma_scale, ycbcr_chroma_midpoint);
ubo->gamma_space_transform[1] = vec4(y_row * luma_scale, luma_offset);
ubo->gamma_space_transform[2] = vec4(cb_row * chroma_scale, ycbcr_chroma_midpoint);

const Primaries bt709 = {
{ 0.640f, 0.330f },
{ 0.300f, 0.600f },
Expand Down
5 changes: 5 additions & 0 deletions video/scaler.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,9 @@ class VideoScaler
};

void set_ycbcr_chroma_midpoint(float midpoint);
// Narrow range follows H.273 at the given bit depth (8 to 16), expressed as normalized UNORM values.
// Full range (the default) ignores bit_depth.
void set_ycbcr_range(VkSamplerYcbcrRange range, unsigned bit_depth);
void rescale(Vulkan::CommandBuffer &cmd, const RescaleInfo &info);

private:
Expand All @@ -58,6 +61,8 @@ class VideoScaler
uint32_t last_input_width = 0, last_input_height = 0;
uint32_t last_output_width = 0, last_output_height = 0;
float ycbcr_chroma_midpoint = 0.5f;
VkSamplerYcbcrRange ycbcr_range = VK_SAMPLER_YCBCR_RANGE_ITU_FULL;
unsigned ycbcr_range_bit_depth = 8;

void update_weights(Vulkan::CommandBuffer &cmd, const RescaleInfo &info);
};
Expand Down
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