Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 106 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-jpeg.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-jpeg.rst
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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+
+.. _jpeg-controls:
+
+**********************
+JPEG Control Reference
+**********************
+
+The JPEG class includes controls for common features of JPEG encoders
+and decoders. Currently it includes features for codecs implementing
+progressive baseline DCT compression process with Huffman entrophy
+coding.
+
+
+.. _jpeg-control-id:
+
+JPEG Control IDs
+================
+
+``V4L2_CID_JPEG_CLASS (class)``
+    The JPEG class descriptor. Calling
+    :ref:`VIDIOC_QUERYCTRL` for this control will
+    return a description of this control class.
+
+``V4L2_CID_JPEG_CHROMA_SUBSAMPLING (menu)``
+    The chroma subsampling factors describe how each component of an
+    input image is sampled, in respect to maximum sample rate in each
+    spatial dimension. See :ref:`itu-t81`, clause A.1.1. for more
+    details. The ``V4L2_CID_JPEG_CHROMA_SUBSAMPLING`` control determines
+    how Cb and Cr components are downsampled after converting an input
+    image from RGB to Y'CbCr color space.
+
+.. tabularcolumns:: |p{7.5cm}|p{10.0cm}|
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+
+    * - ``V4L2_JPEG_CHROMA_SUBSAMPLING_444``
+      - No chroma subsampling, each pixel has Y, Cr and Cb values.
+    * - ``V4L2_JPEG_CHROMA_SUBSAMPLING_422``
+      - Horizontally subsample Cr, Cb components by a factor of 2.
+    * - ``V4L2_JPEG_CHROMA_SUBSAMPLING_420``
+      - Subsample Cr, Cb components horizontally and vertically by 2.
+    * - ``V4L2_JPEG_CHROMA_SUBSAMPLING_411``
+      - Horizontally subsample Cr, Cb components by a factor of 4.
+    * - ``V4L2_JPEG_CHROMA_SUBSAMPLING_410``
+      - Subsample Cr, Cb components horizontally by 4 and vertically by 2.
+    * - ``V4L2_JPEG_CHROMA_SUBSAMPLING_GRAY``
+      - Use only luminance component.
+
+
+
+``V4L2_CID_JPEG_RESTART_INTERVAL (integer)``
+    The restart interval determines an interval of inserting RSTm
+    markers (m = 0..7). The purpose of these markers is to additionally
+    reinitialize the encoder process, in order to process blocks of an
+    image independently. For the lossy compression processes the restart
+    interval unit is MCU (Minimum Coded Unit) and its value is contained
+    in DRI (Define Restart Interval) marker. If
+    ``V4L2_CID_JPEG_RESTART_INTERVAL`` control is set to 0, DRI and RSTm
+    markers will not be inserted.
+
+.. _jpeg-quality-control:
+
+``V4L2_CID_JPEG_COMPRESSION_QUALITY (integer)``
+    ``V4L2_CID_JPEG_COMPRESSION_QUALITY`` control determines trade-off
+    between image quality and size. It provides simpler method for
+    applications to control image quality, without a need for direct
+    reconfiguration of luminance and chrominance quantization tables. In
+    cases where a driver uses quantization tables configured directly by
+    an application, using interfaces defined elsewhere,
+    ``V4L2_CID_JPEG_COMPRESSION_QUALITY`` control should be set by
+    driver to 0.
+
+    The value range of this control is driver-specific. Only positive,
+    non-zero values are meaningful. The recommended range is 1 - 100,
+    where larger values correspond to better image quality.
+
+.. _jpeg-active-marker-control:
+
+``V4L2_CID_JPEG_ACTIVE_MARKER (bitmask)``
+    Specify which JPEG markers are included in compressed stream. This
+    control is valid only for encoders.
+
+
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+
+    * - ``V4L2_JPEG_ACTIVE_MARKER_APP0``
+      - Application data segment APP\ :sub:`0`.
+    * - ``V4L2_JPEG_ACTIVE_MARKER_APP1``
+      - Application data segment APP\ :sub:`1`.
+    * - ``V4L2_JPEG_ACTIVE_MARKER_COM``
+      - Comment segment.
+    * - ``V4L2_JPEG_ACTIVE_MARKER_DQT``
+      - Quantization tables segment.
+    * - ``V4L2_JPEG_ACTIVE_MARKER_DHT``
+      - Huffman tables segment.
+
+
+
+For more details about JPEG specification, refer to :ref:`itu-t81`,
+:ref:`jfif`, :ref:`w3c-jpeg-jfif`.