241 lines
11 KiB
ReStructuredText
241 lines
11 KiB
ReStructuredText
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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******************************
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Single-planar format structure
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******************************
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.. tabularcolumns:: |p{4.0cm}|p{2.6cm}|p{10.7cm}|
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.. c:type:: v4l2_pix_format
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.. cssclass:: longtable
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.. flat-table:: struct v4l2_pix_format
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``width``
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- Image width in pixels.
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* - __u32
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- ``height``
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- Image height in pixels. If ``field`` is one of ``V4L2_FIELD_TOP``,
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``V4L2_FIELD_BOTTOM`` or ``V4L2_FIELD_ALTERNATE`` then height
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refers to the number of lines in the field, otherwise it refers to
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the number of lines in the frame (which is twice the field height
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for interlaced formats).
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* - :cspan:`2` Applications set these fields to request an image
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size, drivers return the closest possible values. In case of
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planar formats the ``width`` and ``height`` applies to the largest
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plane. To avoid ambiguities drivers must return values rounded up
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to a multiple of the scale factor of any smaller planes. For
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example when the image format is YUV 4:2:0, ``width`` and
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``height`` must be multiples of two.
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For compressed formats that contain the resolution information encoded
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inside the stream, when fed to a stateful mem2mem decoder, the fields
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may be zero to rely on the decoder to detect the right values. For more
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details see :ref:`decoder` and format descriptions.
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For compressed formats on the CAPTURE side of a stateful mem2mem
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encoder, the fields must be zero, since the coded size is expected to
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be calculated internally by the encoder itself, based on the OUTPUT
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side. For more details see :ref:`encoder` and format descriptions.
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* - __u32
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- ``pixelformat``
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- The pixel format or type of compression, set by the application.
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This is a little endian
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:ref:`four character code <v4l2-fourcc>`. V4L2 defines standard
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RGB formats in :ref:`pixfmt-rgb`, YUV formats in
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:ref:`yuv-formats`, and reserved codes in
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:ref:`reserved-formats`
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* - __u32
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- ``field``
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- Field order, from enum :c:type:`v4l2_field`.
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Video images are typically interlaced. Applications can request to
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capture or output only the top or bottom field, or both fields
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interlaced or sequentially stored in one buffer or alternating in
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separate buffers. Drivers return the actual field order selected.
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For more details on fields see :ref:`field-order`.
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* - __u32
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- ``bytesperline``
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- Distance in bytes between the leftmost pixels in two adjacent
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lines.
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* - :cspan:`2`
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Both applications and drivers can set this field to request
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padding bytes at the end of each line. Drivers however may ignore
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the value requested by the application, returning ``width`` times
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bytes per pixel or a larger value required by the hardware. That
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implies applications can just set this field to zero to get a
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reasonable default.
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Video hardware may access padding bytes, therefore they must
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reside in accessible memory. Consider cases where padding bytes
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after the last line of an image cross a system page boundary.
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Input devices may write padding bytes, the value is undefined.
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Output devices ignore the contents of padding bytes.
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When the image format is planar the ``bytesperline`` value applies
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to the first plane and is divided by the same factor as the
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``width`` field for the other planes. For example the Cb and Cr
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planes of a YUV 4:2:0 image have half as many padding bytes
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following each line as the Y plane. To avoid ambiguities drivers
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must return a ``bytesperline`` value rounded up to a multiple of
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the scale factor.
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For compressed formats the ``bytesperline`` value makes no sense.
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Applications and drivers must set this to 0 in that case.
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* - __u32
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- ``sizeimage``
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- Size in bytes of the buffer to hold a complete image, set by the
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driver. Usually this is ``bytesperline`` times ``height``. When
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the image consists of variable length compressed data this is the
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number of bytes required by the codec to support the worst-case
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compression scenario.
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The driver will set the value for uncompressed images.
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Clients are allowed to set the sizeimage field for variable length
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compressed data flagged with ``V4L2_FMT_FLAG_COMPRESSED`` at
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:ref:`VIDIOC_ENUM_FMT`, but the driver may ignore it and set the
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value itself, or it may modify the provided value based on
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alignment requirements or minimum/maximum size requirements.
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If the client wants to leave this to the driver, then it should
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set sizeimage to 0.
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* - __u32
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- ``colorspace``
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- Image colorspace, from enum :c:type:`v4l2_colorspace`.
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This information supplements the ``pixelformat`` and must be set
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by the driver for capture streams and by the application for
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output streams, see :ref:`colorspaces`. If the application sets the
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flag ``V4L2_PIX_FMT_FLAG_SET_CSC`` then the application can set
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this field for a capture stream to request a specific colorspace
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for the captured image data. If the driver cannot handle requested
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conversion, it will return another supported colorspace.
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The driver indicates that colorspace conversion is supported by setting
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the flag V4L2_FMT_FLAG_CSC_COLORSPACE in the corresponding struct
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:c:type:`v4l2_fmtdesc` during enumeration. See :ref:`fmtdesc-flags`.
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* - __u32
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- ``priv``
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- This field indicates whether the remaining fields of the
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struct :c:type:`v4l2_pix_format`, also called the
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extended fields, are valid. When set to
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``V4L2_PIX_FMT_PRIV_MAGIC``, it indicates that the extended fields
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have been correctly initialized. When set to any other value it
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indicates that the extended fields contain undefined values.
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Applications that wish to use the pixel format extended fields
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must first ensure that the feature is supported by querying the
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device for the :ref:`V4L2_CAP_EXT_PIX_FORMAT <querycap>`
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capability. If the capability isn't set the pixel format extended
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fields are not supported and using the extended fields will lead
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to undefined results.
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To use the extended fields, applications must set the ``priv``
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field to ``V4L2_PIX_FMT_PRIV_MAGIC``, initialize all the extended
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fields and zero the unused bytes of the
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struct :c:type:`v4l2_format` ``raw_data`` field.
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When the ``priv`` field isn't set to ``V4L2_PIX_FMT_PRIV_MAGIC``
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drivers must act as if all the extended fields were set to zero.
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On return drivers must set the ``priv`` field to
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``V4L2_PIX_FMT_PRIV_MAGIC`` and all the extended fields to
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applicable values.
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* - __u32
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- ``flags``
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- Flags set by the application or driver, see :ref:`format-flags`.
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* - union {
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- (anonymous)
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* - __u32
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- ``ycbcr_enc``
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- Y'CbCr encoding, from enum :c:type:`v4l2_ycbcr_encoding`.
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This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`. If the application sets the
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flag ``V4L2_PIX_FMT_FLAG_SET_CSC`` then the application can set
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this field for a capture stream to request a specific Y'CbCr encoding
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for the captured image data. If the driver cannot handle requested
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conversion, it will return another supported encoding.
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This field is ignored for HSV pixelformats. The driver indicates that
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ycbcr_enc conversion is supported by setting the flag
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V4L2_FMT_FLAG_CSC_YCBCR_ENC in the corresponding struct
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:c:type:`v4l2_fmtdesc` during enumeration. See :ref:`fmtdesc-flags`.
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* - __u32
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- ``hsv_enc``
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- HSV encoding, from enum :c:type:`v4l2_hsv_encoding`.
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This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`. If the application sets the flag
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``V4L2_PIX_FMT_FLAG_SET_CSC`` then the application can set this
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field for a capture stream to request a specific HSV encoding for the
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captured image data. If the driver cannot handle requested
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conversion, it will return another supported encoding.
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This field is ignored for non-HSV pixelformats. The driver indicates
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that hsv_enc conversion is supported by setting the flag
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V4L2_FMT_FLAG_CSC_HSV_ENC in the corresponding struct
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:c:type:`v4l2_fmtdesc` during enumeration. See :ref:`fmtdesc-flags`.
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* - }
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-
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* - __u32
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- ``quantization``
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- Quantization range, from enum :c:type:`v4l2_quantization`.
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This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`. If the application sets the flag
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``V4L2_PIX_FMT_FLAG_SET_CSC`` then the application can set
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this field for a capture stream to request a specific quantization
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range for the captured image data. If the driver cannot handle requested
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conversion, it will return another supported quantization.
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The driver indicates that quantization conversion is supported by setting
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the flag V4L2_FMT_FLAG_CSC_QUANTIZATION in the corresponding struct
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:c:type:`v4l2_fmtdesc` during enumeration. See :ref:`fmtdesc-flags`.
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* - __u32
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- ``xfer_func``
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- Transfer function, from enum :c:type:`v4l2_xfer_func`.
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This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`. If the application sets the flag
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``V4L2_PIX_FMT_FLAG_SET_CSC`` then the application can set
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this field for a capture stream to request a specific transfer function
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for the captured image data. If the driver cannot handle requested
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conversion, it will return another supported transfer function.
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The driver indicates that xfer_func conversion is supported by setting
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the flag V4L2_FMT_FLAG_CSC_XFER_FUNC in the corresponding struct
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:c:type:`v4l2_fmtdesc` during enumeration. See :ref:`fmtdesc-flags`.
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.. tabularcolumns:: |p{6.8cm}|p{2.3cm}|p{8.2cm}|
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.. _format-flags:
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.. flat-table:: Format Flags
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_PIX_FMT_FLAG_PREMUL_ALPHA``
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- 0x00000001
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- The color values are premultiplied by the alpha channel value. For
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example, if a light blue pixel with 50% transparency was described
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by RGBA values (128, 192, 255, 128), the same pixel described with
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premultiplied colors would be described by RGBA values (64, 96,
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128, 128)
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* .. _`v4l2-pix-fmt-flag-set-csc`:
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- ``V4L2_PIX_FMT_FLAG_SET_CSC``
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- 0x00000002
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- Set by the application. It is only used for capture and is
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ignored for output streams. If set, then request the device to do
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colorspace conversion from the received colorspace to the requested
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colorspace values. If the colorimetry field (``colorspace``, ``xfer_func``,
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``ycbcr_enc``, ``hsv_enc`` or ``quantization``) is set to ``*_DEFAULT``,
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then that colorimetry setting will remain unchanged from what was received.
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So in order to change the quantization, only the ``quantization`` field shall
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be set to non default value (``V4L2_QUANTIZATION_FULL_RANGE`` or
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``V4L2_QUANTIZATION_LIM_RANGE``) and all other colorimetry fields shall
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be set to ``*_DEFAULT``.
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To check which conversions are supported by the hardware for the current
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pixel format, see :ref:`fmtdesc-flags`.
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