[libcamera-devel] [RFC PATCH 2/4] libcamera: colorspace: Adjust colorspace of YUV streams

[Umang Jain]

If a YUV stream is requested with no Y'Cbcr encoding, we need to adjust
it to provide a Y'Cbcr encoding. Depending on the transfer function and
primaries specified, a Y'Cbcr encoding is picked up.

Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
---
 include/libcamera/color_space.h |  6 ++++
 src/libcamera/camera.cpp        | 11 ++++++
 src/libcamera/color_space.cpp   | 61 +++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+)

diff --git a/include/libcamera/color_space.h b/include/libcamera/color_space.h
index 0d39fbc0..113e2715 100644
--- a/include/libcamera/color_space.h
+++ b/include/libcamera/color_space.h
@@ -12,6 +12,8 @@
 
 namespace libcamera {
 
+struct StreamConfiguration;
+
 class ColorSpace
 {
 public:
@@ -59,6 +61,10 @@ public:
 
 	std::string toString() const;
 	static std::string toString(const std::optional<ColorSpace> &colorSpace);
+	ColorSpace adjust(const StreamConfiguration &cfg);
+
+private:
+	ColorSpace adjustYuv(const StreamConfiguration &cfg);
 };
 
 bool operator==(const ColorSpace &lhs, const ColorSpace &rhs);
diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp
index 3910915c..05135d16 100644
--- a/src/libcamera/camera.cpp
+++ b/src/libcamera/camera.cpp
@@ -386,6 +386,17 @@ CameraConfiguration::Status CameraConfiguration::validateColorSpaces(ColorSpaceF
 	if (index < 0 || !(flags & ColorSpaceFlag::StreamsShareColorSpace))
 		return status;
 
+	/*
+	 * \todo Question StreamsShareColorSpace <> an adjusted colorspace
+	 * interation.
+	 */
+	if (config_[index].colorSpace) {
+		ColorSpace oldColorspace = config_[index].colorSpace.value();
+		ColorSpace newColorspace = oldColorspace.adjust(config_[index]);
+		if (oldColorspace != newColorspace)
+			config_[index].colorSpace = newColorspace;
+	}
+
 	/* Make all output color spaces the same, if requested. */
 	for (auto &cfg : config_) {
 		if (!isRaw(cfg.pixelFormat) &&
diff --git a/src/libcamera/color_space.cpp b/src/libcamera/color_space.cpp
index 73148228..ff3f76d9 100644
--- a/src/libcamera/color_space.cpp
+++ b/src/libcamera/color_space.cpp
@@ -13,6 +13,10 @@
 #include <sstream>
 #include <utility>
 
+#include <libcamera/stream.h>
+
+#include "libcamera/internal/formats.h"
+
 /**
  * \file color_space.h
  * \brief Class and enums to represent color spaces
@@ -193,6 +197,63 @@ std::string ColorSpace::toString() const
 	return ss.str();
 }
 
+/**
+ * \brief Adjust colospace when stream configuration contains YUV stream
+ * \param[in] config Stream configuration
+ *
+ * This function adjust the stream's colorspace if it consists a YUV stream
+ * and has no Y'Cbcr encoding specified. The function shall update the
+ * Y'Cbcr encoding based on the transfer function and primaries fields.
+ *
+ * \return The adjusted colorspace
+ */
+ColorSpace
+ColorSpace::adjustYuv(const StreamConfiguration &cfg)
+{
+	ColorSpace cs = *this;
+	bool isYUV = (PixelFormatInfo::info(cfg.pixelFormat).colourEncoding ==
+		      PixelFormatInfo::ColourEncodingYUV);
+
+	if (isYUV && cs.ycbcrEncoding == YcbcrEncoding::None) {
+		if (cs.transferFunction == TransferFunction::Rec709) {
+			switch (cs.primaries) {
+			/* Raw should never happen */
+			case Primaries::Raw:
+			case Primaries::Smpte170m:
+				cs.ycbcrEncoding = YcbcrEncoding::Rec601;
+				break;
+			case Primaries::Rec709:
+				cs.ycbcrEncoding = YcbcrEncoding::Rec709;
+				break;
+			case Primaries::Rec2020:
+				cs.ycbcrEncoding = YcbcrEncoding::Rec2020;
+				break;
+			}
+		} else if (cs.transferFunction == TransferFunction::Srgb) {
+			cs.ycbcrEncoding = YcbcrEncoding::Rec601;
+		}
+
+		/* \todo: Determine if range needs to be adjusted in some cases? */
+	}
+
+	return cs;
+}
+
+/**
+ * \brief Adjust the colorspace depending on the stream configuration
+ * \param[in] config Stream configuration
+ *
+ * This function adjust the stream's colorspace depending on various factors
+ * as reflected by the \a config.
+ *
+ * \return The adjusted colorspace according to the stream configuration
+ */
+ColorSpace
+ColorSpace::adjust(const StreamConfiguration &config)
+{
+	return adjustYuv(config);
+}
+
 /**
  * \brief Assemble and return a readable string representation of an
  * optional ColorSpace
-- 
2.31.1