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Diffstat (limited to 'Documentation/DocBook/media/v4l/dev-subdev.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/dev-subdev.xml | 206 |
1 files changed, 180 insertions, 26 deletions
diff --git a/Documentation/DocBook/media/v4l/dev-subdev.xml b/Documentation/DocBook/media/v4l/dev-subdev.xml index 05c8fefcbcb..d15aaf83f56 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 @@ -266,7 +267,7 @@ <para>When satisfied with the try results, applications can set the active formats by setting the <structfield>which</structfield> argument to - <constant>V4L2_SUBDEV_FORMAT_TRY</constant>. Active formats are changed + <constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. Active formats are changed exactly as try formats by drivers. To avoid modifying the hardware state during format negotiation, applications should negotiate try formats first and then modify the active settings using the try formats returned during @@ -275,12 +276,12 @@ </para> </section> - <section> - <title>Cropping and scaling</title> + <section id="v4l2-subdev-selections"> + <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 <xref + linkend="v4l2-selections-common" />.</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_SEL_TGT_COMPOSE</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_SEL_FLAG_GE</constant> and + <constant>V4L2_SEL_FLAG_LE</constant> flags may be + used to round the image size either up or down. <xref + linkend="v4l2-selection-flags" /></para> + </section> + + <section> + <title>Types of selection targets</title> - <para>Cropping behaviour on output pads is not defined.</para> + <section> + <title>Actual targets</title> + + <para>Actual targets (without a postfix) reflect the actual + hardware configuration at any point of time. There is a BOUNDS + target corresponding to every actual target.</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> </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_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><para>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.</para></listitem> + + <listitem><para>Sink pad actual crop selection. The sink pad crop + defines the crop performed to the sink pad format.</para></listitem> + + <listitem><para>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.</para></listitem> + + <listitem><para>Source pad actual crop selection. Crop on the source + pad defines crop performed to the image in the sink compose + bounds rectangle.</para></listitem> + + <listitem><para>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.</para></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; |