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Alpha channel should be 1 by default, rather than 0 #2197

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Alpha channel should be 1 by default, rather than 0 #2197

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1ff4a21
For CPU processor, when source has no alpha make it default to 1.
pennelee Sep 25, 2025
c7b025e
Fix alpha channel for integer types.
pennelee Jan 31, 2026
24c6395
Merge branch 'AcademySoftwareFoundation:main' into feature/1781_2025_…
pennelee Feb 1, 2026
6ffa259
Fix max alpha value to be from input bitdepth not output.
pennelee Feb 3, 2026
fc66696
Forgot to update ImagePacking.h
pennelee Feb 3, 2026
63b7b7a
Merge branch 'AcademySoftwareFoundation:main' into feature/1781_2025_…
pennelee Feb 3, 2026
5a4085b
Remove the unused inputBitDepth name causing compiler error.
pennelee Feb 3, 2026
3066ee8
Update src/OpenColorIO/ImagePacking.cpp
pennelee Feb 3, 2026
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24 changes: 19 additions & 5 deletions src/OpenColorIO/ImagePacking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,8 @@ void Generic<Type>::PackRGBAFromImageDesc(const GenericImageDesc & srcImg,
Type * inBitDepthBuffer,
float * outputBuffer,
int outputBufferSize,
long imagePixelStartIndex)
long imagePixelStartIndex,
BitDepth outputBitDepth)
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@cozdas cozdas Feb 2, 2026

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This function Packs the input image (3 or 4 channel, of type 'Type') into 4-channel f32 buffer, and thus the output bit depth should not be part of the conversion. What needs to be done is to fill the missing input alpha value as the max value the "input" type can represent.

Since the GenericImageDesc class is a simplified version of ImageDesc, it doesn't carry the bithDepth information in it like the ImageDesc does, so you are right to pass it as a separate parameter, but it needs to be the input image bit depth, not the output.

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@pennelee pennelee Feb 3, 2026

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Thank you @cozdas for the helpful explanations!

{
if(outputBuffer==nullptr)
{
Expand Down Expand Up @@ -62,15 +63,21 @@ void Generic<Type>::PackRGBAFromImageDesc(const GenericImageDesc & srcImg,
aPtr = reinterpret_cast<Type*>(aRow + xStrideBytes*xIndex);
}

float maxValue = static_cast<float>(GetBitDepthMaxValue(outputBitDepth));
if (maxValue <= 0)
{
throw Exception("Invalid bit depth max value.");
}

// Process one single, complete scanline.
int pixelsCopied = 0;
while(pixelsCopied < outputBufferSize)
{
{
// Reorder channels from arbitrary channel ordering to RGBA 32-bit float.
inBitDepthBuffer[4*pixelsCopied+0] = *rPtr;
inBitDepthBuffer[4*pixelsCopied+1] = *gPtr;
inBitDepthBuffer[4*pixelsCopied+2] = *bPtr;
inBitDepthBuffer[4*pixelsCopied+3] = aPtr ? *aPtr : (Type)0.0f;
inBitDepthBuffer[4 * pixelsCopied + 3] = aPtr ? *aPtr : (Type)(maxValue);
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@cozdas cozdas Feb 2, 2026

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please keep the formatting consistent with the above lines


pixelsCopied++;
xIndex++;
Expand All @@ -93,7 +100,8 @@ void Generic<float>::PackRGBAFromImageDesc(const GenericImageDesc & srcImg,
float * /*inBitDepthBuffer*/,
float * outputBuffer,
int outputBufferSize,
long imagePixelStartIndex)
long imagePixelStartIndex,
BitDepth outputBitDepth)
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@cozdas cozdas Feb 2, 2026

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this is a specialization of the template function for float input type, so you can simplify this by using hard-coded 1.0f.

{
if(outputBuffer==nullptr)
{
Expand Down Expand Up @@ -132,6 +140,12 @@ void Generic<float>::PackRGBAFromImageDesc(const GenericImageDesc & srcImg,
aPtr = reinterpret_cast<float*>(aRow + xStrideBytes*xIndex);
}

double maxValue = GetBitDepthMaxValue(outputBitDepth);
if (maxValue <= 0)
{
throw Exception("Invalid bit depth max value.");
}

// Process one single, complete scanline.
int pixelsCopied = 0;
while(pixelsCopied < outputBufferSize)
Expand All @@ -140,7 +154,7 @@ void Generic<float>::PackRGBAFromImageDesc(const GenericImageDesc & srcImg,
outputBuffer[4*pixelsCopied+0] = *rPtr;
outputBuffer[4*pixelsCopied+1] = *gPtr;
outputBuffer[4*pixelsCopied+2] = *bPtr;
outputBuffer[4*pixelsCopied+3] = aPtr ? *aPtr : 0.0f;
outputBuffer[4*pixelsCopied+3] = aPtr ? *aPtr : (float)maxValue;

pixelsCopied++;
xIndex++;
Expand Down
3 changes: 2 additions & 1 deletion src/OpenColorIO/ImagePacking.h
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,8 @@ struct Generic
Type * inBitDepthBuffer,
float * outputBuffer,
int outputBufferSize,
long imagePixelStartIndex);
long imagePixelStartIndex,
BitDepth outputBitDepth);

static void UnpackRGBAToImageDesc(GenericImageDesc & dstImg,
float * inputBuffer,
Expand Down
3 changes: 2 additions & 1 deletion src/OpenColorIO/ScanlineHelper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -143,7 +143,8 @@ void GenericScanlineHelper<InType, OutType>::prepRGBAScanline(float** buffer, lo
&m_inBitDepthBuffer[0],
*buffer,
m_dstImg.m_width,
m_yIndex * m_dstImg.m_width);
m_yIndex * m_dstImg.m_width,
m_outputBitDepth);
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@cozdas cozdas Feb 2, 2026

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as explained above, needs to be m_inputBitDepth

}

numPixels = m_dstImg.m_width;
Expand Down
46 changes: 23 additions & 23 deletions tests/cpu/CPUProcessor_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -276,9 +276,9 @@ OCIO_ADD_TEST(CPUProcessor, with_one_matrix)
1.0000f, 1.2500f, 1.9900f };

const std::vector<float> resImg
= { -0.01929f, -0.3995f, 0.4002f, 0.5f,
1.58960f, 0.9050f, 1.5025f, 0.5f,
2.070699f, 1.6505f, 2.4002f, 0.5f };
= { -0.01929f, -0.3995f, 0.4002f, 1.5f,
1.58960f, 0.9050f, 1.5025f, 1.5f,
2.070699f, 1.6505f, 2.4002f, 1.5f };

ComputeValues<OCIO::BIT_DEPTH_F32, OCIO::BIT_DEPTH_F32>(
__LINE__, processor,
Expand Down Expand Up @@ -620,10 +620,10 @@ OCIO_ADD_TEST(CPUProcessor, with_one_1d_lut)
5120, 20480, 65535 };

const std::vector<uint16_t> resImg
= { 95, 24, 0, 0,
268, 178, 123, 0,
955, 598, 394, 0,
65535, 8589, 1986, 0 };
= { 95, 24, 0, 65535,
268, 178, 123, 65535,
955, 598, 394, 65535,
65535, 8589, 1986, 65535 };

ComputeValues<OCIO::BIT_DEPTH_UINT16, OCIO::BIT_DEPTH_UINT16>(
__LINE__, processor,
Expand Down Expand Up @@ -656,10 +656,10 @@ OCIO_ADD_TEST(CPUProcessor, with_one_1d_lut)
128, 1023, 640 };

const std::vector<uint16_t> ui10_resImg
= { 0, 6, 15, 0,
26, 48, 106, 0,
36, 106, 252, 0,
48, 1023, 384, 0 };
= { 0, 6, 15, 1023,
26, 48, 106, 1023,
36, 106, 252, 1023,
48, 1023, 384, 1023 };

ComputeValues<OCIO::BIT_DEPTH_UINT10, OCIO::BIT_DEPTH_UINT10>(
__LINE__, processor,
Expand All @@ -668,10 +668,10 @@ OCIO_ADD_TEST(CPUProcessor, with_one_1d_lut)
NB_PIXELS);

const std::vector<uint16_t> ui16_resImg
= { 0, 394, 955, 0,
1656, 3092, 6794, 0,
2301, 6794, 16162, 0,
3092, 65535, 24593, 0 };
= { 0, 394, 955, 65535,
1656, 3092, 6794, 65535,
2301, 6794, 16162, 65535,
3092, 65535, 24593, 65535 };

ComputeValues<OCIO::BIT_DEPTH_UINT10, OCIO::BIT_DEPTH_UINT16>(
__LINE__, processor,
Expand Down Expand Up @@ -704,21 +704,21 @@ OCIO_ADD_TEST(CPUProcessor, with_one_1d_lut)
1024, 2048, 4095 };

const std::vector<uint16_t> ui12_resImg
= { 0, 11, 25, 0,
37, 60, 103, 0,
49, 103, 193, 0,
424, 1009, 4095, 0 };
= { 0, 11, 25, 4095,
37, 60, 103, 4095,
49, 103, 193, 4095,
424, 1009, 4095, 4095 };

ComputeValues<OCIO::BIT_DEPTH_UINT12, OCIO::BIT_DEPTH_UINT12>(
__LINE__, processor,
&ui12_inImg[0], OCIO::CHANNEL_ORDERING_RGB,
&ui12_resImg[0], OCIO::CHANNEL_ORDERING_RGBA,
NB_PIXELS);
const std::vector<uint16_t> ui16_resImg
= { 0, 178, 394, 0,
598, 955, 1655, 0,
779, 1655, 3089, 0,
6789, 16143, 65535, 0 };
= { 0, 178, 394, 65535,
598, 955, 1655, 65535,
779, 1655, 3089, 65535,
6789, 16143, 65535, 65535 };

ComputeValues<OCIO::BIT_DEPTH_UINT12, OCIO::BIT_DEPTH_UINT16>(
__LINE__, processor,
Expand Down