media/v4l/field-order.rst

13 odd and even field are transmitted, and due to a small delay between
23 object on screen may well move between one field and the next. For
25 which field of a frame is older, the *temporal order*.
27 When the driver provides or accepts images field by field rather than
30 even) fields, the *spatial order*: The first line of the top field is
32 field is the second line of that frame.
35 whether a frame commences with the top or bottom field is pointless. Any
41 Counter to intuition the top field is not necessarily the older field.
42 Whether the older field contains the top or bottom lines is a convention
48 bus in the same order they were captured, so if the top field was
49 captured first (is the older field), the top field is also transmitted
52 All video capture and output devices must report the current field
54 this end applications initialize the ``field`` field of struct
76       - Applications request this field order when any field format
78 	e.g. the requested image size, and return the actual field order.
80 	If multiple field orders are possible the
81 	driver must choose one of the possible field orders during
84 	:c:type:`v4l2_buffer` ``field`` can never be
89         (field-based).
92       - Images consist of the top (aka odd) field only.
95       - Images consist of the bottom (aka even) field only. Applications
102 	order of the fields (whether the top or bottom field is older)
104 	field is the older field. In all other standards the top field
105 	is the older field.
108       - Images contain both fields, the top field lines are stored first
109 	in memory, immediately followed by the bottom field lines. Fields
114       - Images contain both fields, the bottom field lines are stored
115 	first in memory, immediately followed by the top field lines.
121 	temporal order, i. e. the older one first. To indicate the field
122 	parity (whether the current field is a top or bottom field) the
124 	struct :c:type:`v4l2_buffer` ``field`` to
129 	:c:type:`v4l2_buffer` ``sequence`` field. This
131 	since there is no way to communicate if a field was a top or
132 	bottom field.
135       - Images contain both fields, interleaved line by line, top field
136 	first. The top field is the older field.
139       - Images contain both fields, interleaved line by line, top field
140 	first. The bottom field is the older field.