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Diffstat (limited to 'Documentation/DocBook/media/v4l/dev-subdev.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/dev-subdev.xml | 202 |
1 files changed, 178 insertions, 24 deletions
diff --git a/Documentation/DocBook/media/v4l/dev-subdev.xml b/Documentation/DocBook/media/v4l/dev-subdev.xml index 0916a7343a16..4afcbbec5eda 100644 --- a/Documentation/DocBook/media/v4l/dev-subdev.xml +++ b/Documentation/DocBook/media/v4l/dev-subdev.xml @@ -76,11 +76,12 @@ <wordasword>format</wordasword> means the combination of media bus data format, frame width and frame height.</para></note> - <para>Image formats are typically negotiated on video capture and output - devices using the <link linkend="crop">cropping and scaling</link> ioctls. - The driver is responsible for configuring every block in the video pipeline - according to the requested format at the pipeline input and/or - output.</para> + <para>Image formats are typically negotiated on video capture and + output devices using the format and <link + linkend="vidioc-subdev-g-selection">selection</link> ioctls. The + driver is responsible for configuring every block in the video + pipeline according to the requested format at the pipeline input + and/or output.</para> <para>For complex devices, such as often found in embedded systems, identical image sizes at the output of a pipeline can be achieved using @@ -276,11 +277,11 @@ </section> <section> - <title>Cropping and scaling</title> + <title>Selections: cropping, scaling and composition</title> <para>Many sub-devices support cropping frames on their input or output pads (or possible even on both). Cropping is used to select the area of - interest in an image, typically on a video sensor or video decoder. It can + interest in an image, typically on an image sensor or a video decoder. It can also be used as part of digital zoom implementations to select the area of the image that will be scaled up.</para> @@ -288,26 +289,179 @@ &v4l2-rect; by the coordinates of the top left corner and the rectangle size. Both the coordinates and sizes are expressed in pixels.</para> - <para>The crop rectangle is retrieved and set using the - &VIDIOC-SUBDEV-G-CROP; and &VIDIOC-SUBDEV-S-CROP; ioctls. Like for pad - formats, drivers store try and active crop rectangles. The format - negotiation mechanism applies to crop settings as well.</para> - - <para>On input pads, cropping is applied relatively to the current pad - format. The pad format represents the image size as received by the - sub-device from the previous block in the pipeline, and the crop rectangle - represents the sub-image that will be transmitted further inside the - sub-device for processing. The crop rectangle be entirely containted - inside the input image size.</para> - - <para>Input crop rectangle are reset to their default value when the input - image format is modified. Drivers should use the input image size as the - crop rectangle default value, but hardware requirements may prevent this. - </para> + <para>As for pad formats, drivers store try and active + rectangles for the selection targets of ACTUAL type <xref + linkend="v4l2-subdev-selection-targets">.</xref></para> + + <para>On sink pads, cropping is applied relative to the + current pad format. The pad format represents the image size as + received by the sub-device from the previous block in the + pipeline, and the crop rectangle represents the sub-image that + will be transmitted further inside the sub-device for + processing.</para> + + <para>The scaling operation changes the size of the image by + scaling it to new dimensions. The scaling ratio isn't specified + explicitly, but is implied from the original and scaled image + sizes. Both sizes are represented by &v4l2-rect;.</para> + + <para>Scaling support is optional. When supported by a subdev, + the crop rectangle on the subdev's sink pad is scaled to the + size configured using the &VIDIOC-SUBDEV-S-SELECTION; IOCTL + using <constant>V4L2_SUBDEV_SEL_COMPOSE_ACTUAL</constant> + selection target on the same pad. If the subdev supports scaling + but not composing, the top and left values are not used and must + always be set to zero.</para> + + <para>On source pads, cropping is similar to sink pads, with the + exception that the source size from which the cropping is + performed, is the COMPOSE rectangle on the sink pad. In both + sink and source pads, the crop rectangle must be entirely + contained inside the source image size for the crop + operation.</para> + + <para>The drivers should always use the closest possible + rectangle the user requests on all selection targets, unless + specifically told otherwise. + <constant>V4L2_SUBDEV_SEL_FLAG_SIZE_GE</constant> and + <constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant> flags may be + used to round the image size either up or down. <xref + linkend="v4l2-subdev-selection-flags"></xref></para> + </section> + + <section> + <title>Types of selection targets</title> + + <section> + <title>ACTUAL targets</title> + + <para>ACTUAL targets reflect the actual hardware configuration + at any point of time. There is a BOUNDS target + corresponding to every ACTUAL.</para> + </section> + + <section> + <title>BOUNDS targets</title> + + <para>BOUNDS targets is the smallest rectangle that contains + all valid ACTUAL rectangles. It may not be possible to set the + ACTUAL rectangle as large as the BOUNDS rectangle, however. + This may be because e.g. a sensor's pixel array is not + rectangular but cross-shaped or round. The maximum size may + also be smaller than the BOUNDS rectangle.</para> + </section> - <para>Cropping behaviour on output pads is not defined.</para> + </section> + + <section> + <title>Order of configuration and format propagation</title> + + <para>Inside subdevs, the order of image processing steps will + always be from the sink pad towards the source pad. This is also + reflected in the order in which the configuration must be + performed by the user: the changes made will be propagated to + any subsequent stages. If this behaviour is not desired, the + user must set + <constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant> flag. This + flag causes no propagation of the changes are allowed in any + circumstances. This may also cause the accessed rectangle to be + adjusted by the driver, depending on the properties of the + underlying hardware.</para> + + <para>The coordinates to a step always refer to the actual size + of the previous step. The exception to this rule is the source + compose rectangle, which refers to the sink compose bounds + rectangle --- if it is supported by the hardware.</para> + + <orderedlist> + <listitem>Sink pad format. The user configures the sink pad + format. This format defines the parameters of the image the + entity receives through the pad for further processing.</listitem> + + <listitem>Sink pad actual crop selection. The sink pad crop + defines the crop performed to the sink pad format.</listitem> + + <listitem>Sink pad actual compose selection. The size of the + sink pad compose rectangle defines the scaling ratio compared + to the size of the sink pad crop rectangle. The location of + the compose rectangle specifies the location of the actual + sink compose rectangle in the sink compose bounds + rectangle.</listitem> + + <listitem>Source pad actual crop selection. Crop on the source + pad defines crop performed to the image in the sink compose + bounds rectangle.</listitem> + + <listitem>Source pad format. The source pad format defines the + output pixel format of the subdev, as well as the other + parameters with the exception of the image width and height. + Width and height are defined by the size of the source pad + actual crop selection.</listitem> + </orderedlist> + + <para>Accessing any of the above rectangles not supported by the + subdev will return <constant>EINVAL</constant>. Any rectangle + referring to a previous unsupported rectangle coordinates will + instead refer to the previous supported rectangle. For example, + if sink crop is not supported, the compose selection will refer + to the sink pad format dimensions instead.</para> + + <figure id="subdev-image-processing-crop"> + <title>Image processing in subdevs: simple crop example</title> + <mediaobject> + <imageobject> + <imagedata fileref="subdev-image-processing-crop.svg" + format="SVG" scale="200" /> + </imageobject> + </mediaobject> + </figure> + + <para>In the above example, the subdev supports cropping on its + sink pad. To configure it, the user sets the media bus format on + the subdev's sink pad. Now the actual crop rectangle can be set + on the sink pad --- the location and size of this rectangle + reflect the location and size of a rectangle to be cropped from + the sink format. The size of the sink crop rectangle will also + be the size of the format of the subdev's source pad.</para> + + <figure id="subdev-image-processing-scaling-multi-source"> + <title>Image processing in subdevs: scaling with multiple sources</title> + <mediaobject> + <imageobject> + <imagedata fileref="subdev-image-processing-scaling-multi-source.svg" + format="SVG" scale="200" /> + </imageobject> + </mediaobject> + </figure> + + <para>In this example, the subdev is capable of first cropping, + then scaling and finally cropping for two source pads + individually from the resulting scaled image. The location of + the scaled image in the cropped image is ignored in sink compose + target. Both of the locations of the source crop rectangles + refer to the sink scaling rectangle, independently cropping an + area at location specified by the source crop rectangle from + it.</para> + + <figure id="subdev-image-processing-full"> + <title>Image processing in subdevs: scaling and composition + with multiple sinks and sources</title> + <mediaobject> + <imageobject> + <imagedata fileref="subdev-image-processing-full.svg" + format="SVG" scale="200" /> + </imageobject> + </mediaobject> + </figure> + + <para>The subdev driver supports two sink pads and two source + pads. The images from both of the sink pads are individually + cropped, then scaled and further composed on the composition + bounds rectangle. From that, two independent streams are cropped + and sent out of the subdev from the source pads.</para> </section> + </section> &sub-subdev-formats; |