[libcamera-devel] [PATCH v4 4/7] libcamera: colorspace: Rectify the ColorSpace::Srgb preset
paul.elder at ideasonboard.com
paul.elder at ideasonboard.com
Thu Sep 1 05:40:38 CEST 2022
On Tue, Aug 30, 2022 at 01:17:22PM +0530, Umang Jain via libcamera-devel wrote:
> 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 at ideasonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>
> ---
> src/libcamera/color_space.cpp | 18 ++++++++++--------
> src/libcamera/v4l2_device.cpp | 7 +++++--
> 2 files changed, 15 insertions(+), 10 deletions(-)
>
> 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 },
> --
> 2.37.2
>
More information about the libcamera-devel
mailing list