summaryrefslogtreecommitdiffstats
path: root/Documentation/media
diff options
context:
space:
mode:
authorSteve Longerbeam <slongerbeam@gmail.com>2019-05-03 19:45:07 -0400
committerMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-05-28 12:25:37 -0400
commita82c3149ad8b4a84f9737a633250815d5cf0cc5e (patch)
treec94dc0cf566a6c553465f666f9da9ef3d1d42782 /Documentation/media
parent0783525fff6e524532fd613f788e6ce14edba89d (diff)
downloadlinux-a82c3149ad8b4a84f9737a633250815d5cf0cc5e.tar.bz2
media: docs-rst: Clarify older field vs. first transmitted field
Add a paragraph to make it more clear that video equipment will transmit fields in the same order the fields were captured, and replace some of the "is transmitted first" language with "is the older field", since the latter is the important info for motion compensation applications. Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/media')
-rw-r--r--Documentation/media/uapi/v4l/field-order.rst17
1 files changed, 11 insertions, 6 deletions
diff --git a/Documentation/media/uapi/v4l/field-order.rst b/Documentation/media/uapi/v4l/field-order.rst
index d640e922a974..c422bebe4314 100644
--- a/Documentation/media/uapi/v4l/field-order.rst
+++ b/Documentation/media/uapi/v4l/field-order.rst
@@ -51,6 +51,11 @@ determined by the video standard. Hence the distinction between temporal
and spatial order of fields. The diagrams below should make this
clearer.
+In V4L it is assumed that all video cameras transmit fields on the media
+bus in the same order they were captured, so if the top field was
+captured first (is the older field), the top field is also transmitted
+first on the bus.
+
All video capture and output devices must report the current field
order. Some drivers may permit the selection of a different order, to
this end applications initialize the ``field`` field of struct
@@ -101,10 +106,10 @@ enum v4l2_field
* - ``V4L2_FIELD_INTERLACED``
- 4
- Images contain both fields, interleaved line by line. The temporal
- order of the fields (whether the top or bottom field is first
- transmitted) depends on the current video standard. M/NTSC
- transmits the bottom field first, all other standards the top
- field first.
+ order of the fields (whether the top or bottom field is older)
+ depends on the current video standard. In M/NTSC the bottom
+ field is the older field. In all other standards the top field
+ is the older field.
* - ``V4L2_FIELD_SEQ_TB``
- 5
- Images contain both fields, the top field lines are stored first
@@ -135,11 +140,11 @@ enum v4l2_field
* - ``V4L2_FIELD_INTERLACED_TB``
- 8
- Images contain both fields, interleaved line by line, top field
- first. The top field is transmitted first.
+ first. The top field is the older field.
* - ``V4L2_FIELD_INTERLACED_BT``
- 9
- Images contain both fields, interleaved line by line, top field
- first. The bottom field is transmitted first.
+ first. The bottom field is the older field.