libcamera: Add ColorSpace class

This class represents a color space by defining its color primaries,
the transfer (gamma) function it uses, the YCbCr encoding and whether
the output is full or limited range.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

2 files changed, 318 insertions, 0 deletions

diff --git a/src/libcamera/color_space.cpp b/src/libcamera/color_space.cpp
new file mode 100644
index 00000000..895e5c8e
--- /dev/null
+++ b/src/libcamera/color_space.cpp
@@ -0,0 +1,317 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Raspberry Pi (Trading) Limited
+ *
+ * color_space.cpp - color spaces.
+ */
+
+#include <libcamera/color_space.h>
+
+#include <algorithm>
+#include <array>
+#include <map>
+#include <sstream>
+#include <utility>
+
+/**
+ * \file color_space.h
+ * \brief Class and enums to represent color spaces
+ */
+
+namespace libcamera {
+
+/**
+ * \class ColorSpace
+ * \brief Class to describe a color space
+ *
+ * The ColorSpace class defines the color primaries, the transfer function,
+ * the Y'CbCr encoding associated with the color space, and the range
+ * (sometimes also referred to as the quantisation) of the color space.
+ *
+ * Certain combinations of these fields form well-known standard color
+ * spaces such as "JPEG" or "REC709".
+ *
+ * In the strictest sense a "color space" formally only refers to the
+ * color primaries and white point. Here, however, the ColorSpace class
+ * adopts the common broader usage that includes the transfer function,
+ * Y'CbCr encoding method and quantisation.
+ *
+ * For more information on the specific color spaces described here, please
+ * see:
+ *
+ * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-srgb">sRGB</a>
+ * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-jpeg">JPEG</a>
+ * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-smpte-170m">SMPTE 170M</a>
+ * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-rec709">Rec.709</a>
+ * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-bt2020">Rec.2020</a>
+ */
+
+/**
+ * \enum ColorSpace::Primaries
+ * \brief The color primaries for this color space
+ *
+ * \var ColorSpace::Primaries::Raw
+ * \brief These are raw colors directly from a sensor, the primaries are
+ * unspecified
+ *
+ * \var ColorSpace::Primaries::Smpte170m
+ * \brief SMPTE 170M color primaries
+ *
+ * \var ColorSpace::Primaries::Rec709
+ * \brief Rec.709 color primaries
+ *
+ * \var ColorSpace::Primaries::Rec2020
+ * \brief Rec.2020 color primaries
+ */
+
+/**
+ * \enum ColorSpace::TransferFunction
+ * \brief The transfer function used for this color space
+ *
+ * \var ColorSpace::TransferFunction::Linear
+ * \brief This color space uses a linear (identity) transfer function
+ *
+ * \var ColorSpace::TransferFunction::Srgb
+ * \brief sRGB transfer function
+ *
+ * \var ColorSpace::TransferFunction::Rec709
+ * \brief Rec.709 transfer function
+ */
+
+/**
+ * \enum ColorSpace::YcbcrEncoding
+ * \brief The Y'CbCr encoding
+ *
+ * \var ColorSpace::YcbcrEncoding::None
+ * \brief There is no defined Y'CbCr encoding (used for non-YUV formats)
+ *
+ * \var ColorSpace::YcbcrEncoding::Rec601
+ * \brief Rec.601 Y'CbCr encoding
+ *
+ * \var ColorSpace::YcbcrEncoding::Rec709
+ * \brief Rec.709 Y'CbCr encoding
+ *
+ * \var ColorSpace::YcbcrEncoding::Rec2020
+ * \brief Rec.2020 Y'CbCr encoding
+ */
+
+/**
+ * \enum ColorSpace::Range
+ * \brief The range (sometimes "quantisation") for this color space
+ *
+ * \var ColorSpace::Range::Full
+ * \brief This color space uses full range pixel values
+ *
+ * \var ColorSpace::Range::Limited
+ * \brief This color space uses limited range pixel values, being
+ * 16 to 235 for Y' and 16 to 240 for Cb and Cr (8 bits per sample)
+ * or 64 to 940 for Y' and 16 to 960 for Cb and Cr (10 bits)
+ */
+
+/**
+ * \fn ColorSpace::ColorSpace(Primaries p, TransferFunction t, Encoding e, Range r)
+ * \brief Construct a ColorSpace from explicit values
+ * \param[in] p The color primaries
+ * \param[in] t The transfer function for the color space
+ * \param[in] e The Y'CbCr encoding
+ * \param[in] r The range of the pixel values in this color space
+ */
+
+/**
+ * \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
+ * the four constituent parts of the ColorSpace are assembled into a longer
+ * string.
+ *
+ * \return A string describing the ColorSpace
+ */
+std::string ColorSpace::toString() const
+{
+	/* Print out a brief name only for standard color spaces. */
+
+	static const std::array<std::pair<ColorSpace, const char *>, 6> colorSpaceNames = { {
+		{ ColorSpace::Raw, "RAW" },
+		{ ColorSpace::Jpeg, "JPEG" },
+		{ ColorSpace::Srgb, "sRGB" },
+		{ ColorSpace::Smpte170m, "SMPTE170M" },
+		{ ColorSpace::Rec709, "Rec709" },
+		{ ColorSpace::Rec2020, "Rec2020" },
+	} };
+	auto it = std::find_if(colorSpaceNames.begin(), colorSpaceNames.end(),
+			       [this](const auto &item) {
+				       return *this == item.first;
+			       });
+	if (it != colorSpaceNames.end())
+		return std::string(it->second);
+
+	/* Assemble a name made of the constituent fields. */
+
+	static const std::map<Primaries, std::string> primariesNames = {
+		{ Primaries::Raw, "RAW" },
+		{ Primaries::Smpte170m, "SMPTE170M" },
+		{ Primaries::Rec709, "Rec709" },
+		{ Primaries::Rec2020, "Rec2020" },
+	};
+	static const std::map<TransferFunction, std::string> transferNames = {
+		{ TransferFunction::Linear, "Linear" },
+		{ TransferFunction::Srgb, "sRGB" },
+		{ TransferFunction::Rec709, "Rec709" },
+	};
+	static const std::map<YcbcrEncoding, std::string> encodingNames = {
+		{ YcbcrEncoding::None, "None" },
+		{ YcbcrEncoding::Rec601, "Rec601" },
+		{ YcbcrEncoding::Rec709, "Rec709" },
+		{ YcbcrEncoding::Rec2020, "Rec2020" },
+	};
+	static const std::map<Range, std::string> rangeNames = {
+		{ Range::Full, "Full" },
+		{ Range::Limited, "Limited" },
+	};
+
+	auto itPrimaries = primariesNames.find(primaries);
+	std::string primariesName =
+		itPrimaries == primariesNames.end() ? "Invalid" : itPrimaries->second;
+
+	auto itTransfer = transferNames.find(transferFunction);
+	std::string transferName =
+		itTransfer == transferNames.end() ? "Invalid" : itTransfer->second;
+
+	auto itEncoding = encodingNames.find(ycbcrEncoding);
+	std::string encodingName =
+		itEncoding == encodingNames.end() ? "Invalid" : itEncoding->second;
+
+	auto itRange = rangeNames.find(range);
+	std::string rangeName =
+		itRange == rangeNames.end() ? "Invalid" : itRange->second;
+
+	std::stringstream ss;
+	ss << primariesName << "/" << transferName << "/" << encodingName << "/" << rangeName;
+
+	return ss.str();
+}
+
+/**
+ * \brief Assemble and return a readable string representation of an
+ * optional ColorSpace
+ *
+ * This is a convenience helper to easily obtain a string representation
+ * for a ColorSpace in parts of the libcamera API where it is stored in a
+ * std::optional<>. If the ColorSpace is set, this function returns
+ * \a colorSpace.toString(), otherwise it returns "Unset".
+ *
+ * \return A string describing the optional ColorSpace
+ */
+std::string ColorSpace::toString(const std::optional<ColorSpace> &colorSpace)
+{
+	if (!colorSpace)
+		return "Unset";
+
+	return colorSpace->toString();
+}
+
+/**
+ * \var ColorSpace::primaries
+ * \brief The color primaries of this color space
+ */
+
+/**
+ * \var ColorSpace::transferFunction
+ * \brief The transfer function used by this color space
+ */
+
+/**
+ * \var ColorSpace::ycbcrEncoding
+ * \brief The Y'CbCr encoding used by this color space
+ */
+
+/**
+ * \var ColorSpace::range
+ * \brief The pixel range used with by color space
+ */
+
+/**
+ * \brief A constant representing a raw color space (from a sensor)
+ */
+const ColorSpace ColorSpace::Raw = {
+	Primaries::Raw,
+	TransferFunction::Linear,
+	YcbcrEncoding::None,
+	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
+ *
+ * This is identical to the JPEG color space except that the Y'CbCr
+ * range is limited rather than full.
+ */
+const ColorSpace ColorSpace::Srgb = {
+	Primaries::Rec709,
+	TransferFunction::Srgb,
+	YcbcrEncoding::Rec601,
+	Range::Limited
+};
+
+/**
+ * \brief A constant representing the SMPTE170M color space
+ */
+const ColorSpace ColorSpace::Smpte170m = {
+	Primaries::Smpte170m,
+	TransferFunction::Rec709,
+	YcbcrEncoding::Rec601,
+	Range::Limited
+};
+
+/**
+ * \brief A constant representing the Rec.709 color space
+ */
+const ColorSpace ColorSpace::Rec709 = {
+	Primaries::Rec709,
+	TransferFunction::Rec709,
+	YcbcrEncoding::Rec709,
+	Range::Limited
+};
+
+/**
+ * \brief A constant representing the Rec.2020 color space
+ */
+const ColorSpace ColorSpace::Rec2020 = {
+	Primaries::Rec2020,
+	TransferFunction::Rec709,
+	YcbcrEncoding::Rec2020,
+	Range::Limited
+};
+
+/**
+ * \brief Compare color spaces for equality
+ * \return True if the two color spaces are identical, false otherwise
+ */
+bool operator==(const ColorSpace &lhs, const ColorSpace &rhs)
+{
+	return lhs.primaries == rhs.primaries &&
+	       lhs.transferFunction == rhs.transferFunction &&
+	       lhs.ycbcrEncoding == rhs.ycbcrEncoding &&
+	       lhs.range == rhs.range;
+}
+
+/**
+ * \fn bool operator!=(const ColorSpace &lhs, const ColorSpace &rhs)
+ * \brief Compare color spaces for inequality
+ * \return True if the two color spaces are not identical, false otherwise
+ */
+
+} /* namespace libcamera */
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index dc1cc52a..7ae909d4 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -9,6 +9,7 @@ libcamera_sources = files([
     'camera_manager.cpp',
     'camera_sensor.cpp',
     'camera_sensor_properties.cpp',
+    'color_space.cpp',
     'controls.cpp',
     'control_serializer.cpp',
     'control_validator.cpp',