Working on SoftISP
a17f0eddc6
The JPEG color space is badly name, as the JPEG specification (ITU-T
T.81) doesn't define any particular color space:
The interchange format does not specify a complete coded image
representation. Application-dependent information, e.g. colour
space, is outside the scope of this Specification.
The JFIF specification (ITU-T T.871) is clearer as it requires ITU-R
BT.601 YCbCr encoding and a full quantization range:
The interpretations of Y, CB, and CR are derived from the E'Y, E'Cb,
and E'Cr signals defined in the 625-line specification of Rec. ITU-R
BT.601, but these signals are normalized so as to permit the usage of
the full range of 256 levels of the 8-bit binary encoding of the Y
component.
It however doesn't specify color primaries or a transfer function
explicitly. It only mentions the latter when describing the conversion
from YCbCr to RGB:
The inverse relationship for computing full scale 8-bit per colour
channel gamma pre-corrected RGB values (following Rec. ITU-R BT.601
gamma pre-correction and colour primary specifications) from YCbCr
colours (with 256 levels per component) can be computed as follows:
[...]
Given that ITU-R BT.601-5 (1995) didn't specify color primaries or a
transfer function, and that the later ITU-R BT.601-7 (2011) version
specifies color primaries for the 625-line variant that do not match
sRGB, the JPEG color space in libcamera is badly named. This is
confirmed by ITU-T T.871:
As this Recommendation | International Standard is based on the prior
informally-circulated JFIF version 1.02 specification that was
produced in 1992, which referenced Rec. ITU-R BT.601 (formerly CCIR
601), it references that specification for definition of the E'Y,
E'Cb, and E'Cr signals that correspond to the YCBCR values specified
herein. However, since the development of the prior JFIF version 1.02
specification, additional industry specifications have been developed,
Rec. ITU-R BT.601 has been updated, and common industry practice has
emerged which often follows the sYCC specification in IEC
61966-2-1/Amd.1. The difference between the use of the colour
interpretation specification in this Recommendation | International
Standard and that of the sYCC specification may be considered
negligible in practice.
Rename the color space to sYCC, as its definition matches the sYCC
standard, and indicate that it is typically used to encode JPEG images.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
|
||
|---|---|---|
| .reuse | ||
| Documentation | ||
| include | ||
| LICENSES | ||
| package/gentoo/media-libs/libcamera | ||
| src | ||
| subprojects | ||
| test | ||
| utils | ||
| .clang-format | ||
| .clang-tidy | ||
| .gitignore | ||
| COPYING.rst | ||
| meson.build | ||
| meson_options.txt | ||
| README.rst | ||
.. SPDX-License-Identifier: CC-BY-SA-4.0
.. section-begin-libcamera
===========
libcamera
===========
**A complex camera support library for Linux, Android, and ChromeOS**
Cameras are complex devices that need heavy hardware image processing
operations. Control of the processing is based on advanced algorithms that must
run on a programmable processor. This has traditionally been implemented in a
dedicated MCU in the camera, but in embedded devices algorithms have been moved
to the main CPU to save cost. Blurring the boundary between camera devices and
Linux often left the user with no other option than a vendor-specific
closed-source solution.
To address this problem the Linux media community has very recently started
collaboration with the industry to develop a camera stack that will be
open-source-friendly while still protecting vendor core IP. libcamera was born
out of that collaboration and will offer modern camera support to Linux-based
systems, including traditional Linux distributions, ChromeOS and Android.
.. section-end-libcamera
.. section-begin-getting-started
Getting Started
---------------
To fetch the sources, build and install:
::
git clone https://git.libcamera.org/libcamera/libcamera.git
cd libcamera
meson build
ninja -C build install
Dependencies
~~~~~~~~~~~~
The following Debian/Ubuntu packages are required for building libcamera.
Other distributions may have differing package names:
A C++ toolchain: [required]
Either {g++, clang}
Meson Build system: [required]
meson (>= 0.56) ninja-build pkg-config
If your distribution doesn't provide a recent enough version of meson,
you can install or upgrade it using pip3.
.. code::
pip3 install --user meson
pip3 install --user --upgrade meson
for the libcamera core: [required]
libyaml-dev python3-yaml python3-ply python3-jinja2
for IPA module signing: [recommended]
Either libgnutls28-dev or libssl-dev, openssl
Without IPA module signing, all IPA modules will be isolated in a
separate process. This adds an unnecessary extra overhead at runtime.
for improved debugging: [optional]
libdw-dev libunwind-dev
libdw and libunwind provide backtraces to help debugging assertion
failures. Their functions overlap, libdw provides the most detailed
information, and libunwind is not needed if both libdw and the glibc
backtrace() function are available.
for device hotplug enumeration: [optional]
libudev-dev
for documentation: [optional]
python3-sphinx doxygen graphviz texlive-latex-extra
for gstreamer: [optional]
libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev
for cam: [optional]
libevent-dev is required to support cam, however the following
optional dependencies bring more functionality to the cam test
tool:
- libdrm-dev: Enables the KMS sink
- libjpeg-dev: Enables MJPEG on the SDL sink
- libsdl2-dev: Enables the SDL sink
for qcam: [optional]
qtbase5-dev libqt5core5a libqt5gui5 libqt5widgets5 qttools5-dev-tools libtiff-dev
for tracing with lttng: [optional]
liblttng-ust-dev python3-jinja2 lttng-tools
for android: [optional]
libexif-dev libjpeg-dev
for lc-compliance: [optional]
libevent-dev
Basic testing with cam utility
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``cam`` utility can be used for basic testing. You can list the cameras
detected on the system with ``cam -l``, and capture ten frames from the first
camera and save them to disk with ``cam -c 1 --capture=10 --file``. See
``cam -h`` for more information about the ``cam`` tool.
In case of problems, a detailed debug log can be obtained from libcamera by
setting the ``LIBCAMERA_LOG_LEVELS`` environment variable:
.. code::
:~$ LIBCAMERA_LOG_LEVELS=*:DEBUG cam -l
Using GStreamer plugin
~~~~~~~~~~~~~~~~~~~~~~
To use GStreamer plugin from source tree, set the following environment so that
GStreamer can find it. This isn't necessary when libcamera is installed.
export GST_PLUGIN_PATH=$(pwd)/build/src/gstreamer
The debugging tool ``gst-launch-1.0`` can be used to construct a pipeline and
test it. The following pipeline will stream from the camera named "Camera 1"
onto the OpenGL accelerated display element on your system.
.. code::
gst-launch-1.0 libcamerasrc camera-name="Camera 1" ! glimagesink
To show the first camera found you can omit the camera-name property, or you
can list the cameras and their capabilities using:
.. code::
gst-device-monitor-1.0 Video
This will also show the supported stream sizes which can be manually selected
if desired with a pipeline such as:
.. code::
gst-launch-1.0 libcamerasrc ! 'video/x-raw,width=1280,height=720' ! \
glimagesink
The libcamerasrc element has two log categories, named libcamera-provider (for
the video device provider) and libcamerasrc (for the operation of the camera).
All corresponding debug messages can be enabled by setting the ``GST_DEBUG``
environment variable to ``libcamera*:7``.
Presently, to prevent element negotiation failures it is required to specify
the colorimetry and framerate as part of your pipeline construction. For
instance, to capture and encode as a JPEG stream and receive on another device
the following example could be used as a starting point:
.. code::
gst-launch-1.0 libcamerasrc ! \
video/x-raw,colorimetry=bt709,format=NV12,width=1280,height=720,framerate=30/1 ! \
jpegenc ! multipartmux ! \
tcpserversink host=0.0.0.0 port=5000
Which can be received on another device over the network with:
.. code::
gst-launch-1.0 tcpclientsrc host=$DEVICE_IP port=5000 ! \
multipartdemux ! jpegdec ! autovideosink
.. section-end-getting-started
Troubleshooting
~~~~~~~~~~~~~~~
Several users have reported issues with meson installation, crux of the issue
is a potential version mismatch between the version that root uses, and the
version that the normal user uses. On calling `ninja -C build`, it can't find
the build.ninja module. This is a snippet of the error message.
::
ninja: Entering directory `build'
ninja: error: loading 'build.ninja': No such file or directory
This can be solved in two ways:
1) Don't install meson again if it is already installed system-wide.
2) If a version of meson which is different from the system-wide version is
already installed, uninstall that meson using pip3, and install again without
the --user argument.