summaryrefslogtreecommitdiffstats
path: root/Documentation/DocBook/media/v4l/dev-subdev.xml
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/DocBook/media/v4l/dev-subdev.xml')
-rw-r--r--Documentation/DocBook/media/v4l/dev-subdev.xml202
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 0916a73..4afcbbe 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;