[libcamera-devel] [PATCH] libcamera: color_space: Rename Jpeg to Sycc
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Wed Aug 17 23:18:24 CEST 2022
The JPEG color space is badly name, as the JPEG specification (ITU-T
T.81) doesn't define any particular color space:
The interchange format does not specify a complete coded image
representation. Application-dependent information, e.g. colour
space, is outside the scope of this Specification.
The JFIF specification (ITU-T T.871) is clearer as it requires ITU-R
BT.601 YCbCr encoding and a full quantization range:
The interpretations of Y, CB, and CR are derived from the E'Y, E'Cb,
and E'Cr signals defined in the 625-line specification of Rec. ITU-R
BT.601, but these signals are normalized so as to permit the usage of
the full range of 256 levels of the 8-bit binary encoding of the Y
component.
It however doesn't specify color primaries or a transfer function
explicitly. It only mentions the latter when describing the conversion
from YCbCr to RGB:
The inverse relationship for computing full scale 8-bit per colour
channel gamma pre-corrected RGB values (following Rec. ITU-R BT.601
gamma pre-correction and colour primary specifications) from YCbCr
colours (with 256 levels per component) can be computed as follows:
[...]
Given that ITU-R BT.601-5 (1995) didn't specify color primaries or a
transfer function, and that the later ITU-R BT.601-7 (2011) version
specifies color primaries for the 625-line variant that do not match
sRGB, the JPEG color space in libcamera is badly named.
Rename the color space to sYCC, as its definition matches the sYCC
standard, and indicate that it is typically used to encode JPEG images.
Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
Hans, following our discussion on IRC, I double-check the JFIF standard,
and my findings are described in the commit message above. It seems that
naming the color space "JPEG" in V4L2 is actually incorrect, as JFIF
expects the 626-line ITU-R BT.601 chromaticities for the primary colors,
which are slightly different than sRGB (the 525-line chromaticities
match SMPTE 170M and SMPTE 240M, but not sRGB either). It seems that we
are missing a V4L2_COLORSPACE_* value to describe the 625-line ITU-R
BT.601 chromaticities, is that an oversight ?
---
include/libcamera/color_space.h | 2 +-
src/libcamera/color_space.cpp | 28 +++++++++----------
.../pipeline/raspberrypi/raspberrypi.cpp | 10 +++----
src/libcamera/v4l2_device.cpp | 4 +--
src/py/libcamera/py_main.cpp | 2 +-
5 files changed, 23 insertions(+), 23 deletions(-)
diff --git a/include/libcamera/color_space.h b/include/libcamera/color_space.h
index 0d39fbc02220..8030a264c66f 100644
--- a/include/libcamera/color_space.h
+++ b/include/libcamera/color_space.h
@@ -46,8 +46,8 @@ public:
}
static const ColorSpace Raw;
- static const ColorSpace Jpeg;
static const ColorSpace Srgb;
+ static const ColorSpace Sycc;
static const ColorSpace Smpte170m;
static const ColorSpace Rec709;
static const ColorSpace Rec2020;
diff --git a/src/libcamera/color_space.cpp b/src/libcamera/color_space.cpp
index caf397607b10..6ace40dcb0fb 100644
--- a/src/libcamera/color_space.cpp
+++ b/src/libcamera/color_space.cpp
@@ -121,8 +121,8 @@ namespace libcamera {
* \brief Assemble and return a readable string representation of the
* ColorSpace
*
- * If the color space matches a standard ColorSpace (such as ColorSpace::Jpeg)
- * then the short name of the color space ("JPEG") is returned. Otherwise
+ * If the color space matches a standard ColorSpace (such as ColorSpace::Sycc)
+ * then the short name of the color space ("sYCC") is returned. Otherwise
* the four constituent parts of the ColorSpace are assembled into a longer
* string.
*
@@ -134,8 +134,8 @@ std::string ColorSpace::toString() const
static const std::array<std::pair<ColorSpace, const char *>, 6> colorSpaceNames = { {
{ ColorSpace::Raw, "RAW" },
- { ColorSpace::Jpeg, "JPEG" },
{ ColorSpace::Srgb, "sRGB" },
+ { ColorSpace::Sycc, "sYCC" },
{ ColorSpace::Smpte170m, "SMPTE170M" },
{ ColorSpace::Rec709, "Rec709" },
{ ColorSpace::Rec2020, "Rec2020" },
@@ -242,17 +242,6 @@ const ColorSpace ColorSpace::Raw = {
Range::Full
};
-/**
- * \brief A constant representing the JPEG color space used for
- * encoding JPEG images
- */
-const ColorSpace ColorSpace::Jpeg = {
- Primaries::Rec709,
- TransferFunction::Srgb,
- YcbcrEncoding::Rec601,
- Range::Full
-};
-
/**
* \brief A constant representing the sRGB color space
*
@@ -266,6 +255,17 @@ const ColorSpace ColorSpace::Srgb = {
Range::Limited
};
+/**
+ * \brief A constant representing the sYCC color space, typically used for
+ * encoding JPEG images
+ */
+const ColorSpace ColorSpace::Sycc = {
+ Primaries::Rec709,
+ TransferFunction::Srgb,
+ YcbcrEncoding::Rec601,
+ Range::Full
+};
+
/**
* \brief A constant representing the SMPTE170M color space
*/
diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
index e895584d4fbc..b4094898ca6c 100644
--- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
+++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
@@ -593,11 +593,11 @@ CameraConfiguration *PipelineHandlerRPi::generateConfiguration(Camera *camera,
fmts = data->isp_[Isp::Output0].dev()->formats();
pixelFormat = formats::NV12;
/*
- * Still image codecs usually expect the JPEG color space.
+ * Still image codecs usually expect the sYCC color space.
* Even RGB codecs will be fine as the RGB we get with the
- * JPEG color space is the same as sRGB.
+ * sYCC color space is the same as sRGB.
*/
- colorSpace = ColorSpace::Jpeg;
+ colorSpace = ColorSpace::Sycc;
/* Return the largest sensor resolution. */
size = sensorSize;
bufferCount = 1;
@@ -628,7 +628,7 @@ CameraConfiguration *PipelineHandlerRPi::generateConfiguration(Camera *camera,
case StreamRole::Viewfinder:
fmts = data->isp_[Isp::Output0].dev()->formats();
pixelFormat = formats::ARGB8888;
- colorSpace = ColorSpace::Jpeg;
+ colorSpace = ColorSpace::Sycc;
size = { 800, 600 };
bufferCount = 4;
outCount++;
@@ -835,7 +835,7 @@ int PipelineHandlerRPi::configure(Camera *camera, CameraConfiguration *config)
format.size = maxSize;
format.fourcc = dev->toV4L2PixelFormat(formats::YUV420);
/* No one asked for output, so the color space doesn't matter. */
- format.colorSpace = ColorSpace::Jpeg;
+ format.colorSpace = ColorSpace::Sycc;
ret = dev->setFormat(&format);
if (ret) {
LOG(RPI, Error)
diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
index 3fc8438f6579..b22a981ff1a6 100644
--- a/src/libcamera/v4l2_device.cpp
+++ b/src/libcamera/v4l2_device.cpp
@@ -745,8 +745,8 @@ void V4L2Device::eventAvailable()
static const std::map<uint32_t, ColorSpace> v4l2ToColorSpace = {
{ V4L2_COLORSPACE_RAW, ColorSpace::Raw },
- { V4L2_COLORSPACE_JPEG, ColorSpace::Jpeg },
{ V4L2_COLORSPACE_SRGB, ColorSpace::Srgb },
+ { V4L2_COLORSPACE_JPEG, ColorSpace::Sycc },
{ V4L2_COLORSPACE_SMPTE170M, ColorSpace::Smpte170m },
{ V4L2_COLORSPACE_REC709, ColorSpace::Rec709 },
{ V4L2_COLORSPACE_BT2020, ColorSpace::Rec2020 },
@@ -771,8 +771,8 @@ static const std::map<uint32_t, ColorSpace::Range> v4l2ToRange = {
static const std::vector<std::pair<ColorSpace, v4l2_colorspace>> colorSpaceToV4l2 = {
{ ColorSpace::Raw, V4L2_COLORSPACE_RAW },
- { ColorSpace::Jpeg, V4L2_COLORSPACE_JPEG },
{ ColorSpace::Srgb, V4L2_COLORSPACE_SRGB },
+ { ColorSpace::Sycc, V4L2_COLORSPACE_JPEG },
{ ColorSpace::Smpte170m, V4L2_COLORSPACE_SMPTE170M },
{ ColorSpace::Rec709, V4L2_COLORSPACE_REC709 },
{ ColorSpace::Rec2020, V4L2_COLORSPACE_BT2020 },
diff --git a/src/py/libcamera/py_main.cpp b/src/py/libcamera/py_main.cpp
index 505cc3dc1a0d..2a58e34a7cdb 100644
--- a/src/py/libcamera/py_main.cpp
+++ b/src/py/libcamera/py_main.cpp
@@ -602,8 +602,8 @@ PYBIND11_MODULE(_libcamera, m)
.def_readwrite("ycbcrEncoding", &ColorSpace::ycbcrEncoding)
.def_readwrite("range", &ColorSpace::range)
.def_static("Raw", []() { return ColorSpace::Raw; })
- .def_static("Jpeg", []() { return ColorSpace::Jpeg; })
.def_static("Srgb", []() { return ColorSpace::Srgb; })
+ .def_static("Sycc", []() { return ColorSpace::Sycc; })
.def_static("Smpte170m", []() { return ColorSpace::Smpte170m; })
.def_static("Rec709", []() { return ColorSpace::Rec709; })
.def_static("Rec2020", []() { return ColorSpace::Rec2020; });
--
Regards,
Laurent Pinchart
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