[libcamera-devel] [PATCH v2 3/6] libcamera: colorspace: Rectify the ColorSpace::Srgb preset

[Umang Jain]

Rectify the ColorSpace::Srgb to denote that it does not use
any Y'Cbcr encoding and uses full range.

The kernel on the other hand, recommends to use Rec601 as the encoding
for V4L2_COLORSPACE_SRGB. It is not very explicit but it can be
inferred that the kernel assumes V4L2_COLORSPACE_SRGB is a YUV-encoded
one. However, when the data is in RGB, no encoding is required (and
this is denoted by YcbcrEncoding::None in libcamera).

Hence, to be clear on the libcamera colorspace API, rectify the
ColorSpace::Srgb preset to use YcbcrEncoding::None.

Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
---
 src/libcamera/color_space.cpp | 14 +++++++-------
 src/libcamera/v4l2_device.cpp |  7 +++++--
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/libcamera/color_space.cpp b/src/libcamera/color_space.cpp
index f0d6109a..cb47acf9 100644
--- a/src/libcamera/color_space.cpp
+++ b/src/libcamera/color_space.cpp
@@ -47,7 +47,10 @@ namespace libcamera {
  *
  * Note that there is no guarantee of a 1:1 mapping between color space names
  * and definitions in libcamera and V4L2. A notable difference is that the sYCC
- * libcamera color space is called JPEG in V4L2 due to historical reasons.
+ * libcamera color space is called JPEG in V4L2 due to historical reasons. On
+ * a similar note, the sRGB colorspace defined in the kernel assumes a Y'CbCr
+ * encoding to it which is not true. Hence the ColorSpace::sRGB is defined
+ * differently in libcamera (with no Y'CbCr encoding and full range).
  *
  * \todo Define the color space fully in the libcamera API to avoid referencing
  * V4L2
@@ -250,16 +253,13 @@ const ColorSpace ColorSpace::Raw = {
 };
 
 /**
- * \brief A constant representing the sRGB color space
- *
- * This is identical to the sYCC color space except that the Y'CbCr
- * range is limited rather than full.
+ * \brief A constant representing the sRGB color space (RGB formats only)
  */
 const ColorSpace ColorSpace::Srgb = {
 	Primaries::Rec709,
 	TransferFunction::Srgb,
-	YcbcrEncoding::Rec601,
-	Range::Limited
+	YcbcrEncoding::None,
+	Range::Full
 };
 
 /**
diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
index 1fb08b9d..a9e34ee1 100644
--- a/src/libcamera/v4l2_device.cpp
+++ b/src/libcamera/v4l2_device.cpp
@@ -746,7 +746,11 @@ void V4L2Device::eventAvailable()
 
 static const std::map<uint32_t, ColorSpace> v4l2ToColorSpace = {
 	{ V4L2_COLORSPACE_RAW, ColorSpace::Raw },
-	{ V4L2_COLORSPACE_SRGB, ColorSpace::Srgb },
+	{ V4L2_COLORSPACE_SRGB, {
+		ColorSpace::Primaries::Rec709,
+		ColorSpace::TransferFunction::Srgb,
+		ColorSpace::YcbcrEncoding::Rec601,
+		ColorSpace::Range::Limited } },
 	{ V4L2_COLORSPACE_JPEG, ColorSpace::Sycc },
 	{ V4L2_COLORSPACE_SMPTE170M, ColorSpace::Smpte170m },
 	{ V4L2_COLORSPACE_REC709, ColorSpace::Rec709 },
@@ -772,7 +776,6 @@ 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::Srgb, V4L2_COLORSPACE_SRGB },
 	{ ColorSpace::Sycc, V4L2_COLORSPACE_JPEG },
 	{ ColorSpace::Smpte170m, V4L2_COLORSPACE_SMPTE170M },
 	{ ColorSpace::Rec709, V4L2_COLORSPACE_REC709 },
-- 
2.35.1