From d09c2bb127d5f96f4f397bd3ca11839840888b46 Mon Sep 17 00:00:00 2001
From: Umang Jain <umang.jain@ideasonboard.com>
Date: Tue, 30 Aug 2022 13:17:22 +0530
Subject: libcamera: colorspace: Rectify the ColorSpace::Srgb preset

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 and full range.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
---
 src/libcamera/color_space.cpp | 18 ++++++++++--------
 src/libcamera/v4l2_device.cpp |  7 +++++--
 2 files changed, 15 insertions(+), 10 deletions(-)

(limited to 'src/libcamera')

diff --git a/src/libcamera/color_space.cpp b/src/libcamera/color_space.cpp
index 944d0e98..ec34620a 100644
--- a/src/libcamera/color_space.cpp
+++ b/src/libcamera/color_space.cpp
@@ -49,8 +49,13 @@ namespace libcamera {
  * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-bt2020">Rec.2020</a>
  *
  * 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.
+ * and definitions in libcamera and V4L2. Two notable differences are
+ *
+ * - The sRGB libcamera color space is defined for RGB formats only with no
+ *   Y'CbCr encoding and a full quantization range, while the V4L2 SRGB color
+ *   space has a Y'CbCr encoding and a limited quantization range.
+ * - The sYCC libcamera color space is called JPEG in V4L2 due to historical
+ *   reasons.
  *
  * \todo Define the color space fully in the libcamera API to avoid referencing
  * V4L2
@@ -138,16 +143,13 @@ 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 301620f8..1d899657 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 },
-- 
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