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+.. -*- coding: utf-8; mode: rst -*-
+
+**********************
+Standard Image Formats
+**********************
+
+In order to exchange images between drivers and applications, it is
+necessary to have standard image data formats which both sides will
+interpret the same way. V4L2 includes several such formats, and this
+section is intended to be an unambiguous specification of the standard
+image data formats in V4L2.
+
+V4L2 drivers are not limited to these formats, however. Driver-specific
+formats are possible. In that case the application may depend on a codec
+to convert images to one of the standard formats when needed. But the
+data can still be stored and retrieved in the proprietary format. For
+example, a device may support a proprietary compressed format.
+Applications can still capture and save the data in the compressed
+format, saving much disk space, and later use a codec to convert the
+images to the X Windows screen format when the video is to be displayed.
+
+Even so, ultimately, some standard formats are needed, so the V4L2
+specification would not be complete without well-defined standard
+formats.
+
+The V4L2 standard formats are mainly uncompressed formats. The pixels
+are always arranged in memory from left to right, and from top to
+bottom. The first byte of data in the image buffer is always for the
+leftmost pixel of the topmost row. Following that is the pixel
+immediately to its right, and so on until the end of the top row of
+pixels. Following the rightmost pixel of the row there may be zero or
+more bytes of padding to guarantee that each row of pixel data has a
+certain alignment. Following the pad bytes, if any, is data for the
+leftmost pixel of the second row from the top, and so on. The last row
+has just as many pad bytes after it as the other rows.
+
+In V4L2 each format has an identifier which looks like ``PIX_FMT_XXX``,
+defined in the :ref:`videodev2.h <videodev>` header file. These
+identifiers represent
+:ref:`four character (FourCC) codes <v4l2-fourcc>` which are also
+listed below, however they are not the same as those used in the Windows
+world.
+
+For some formats, data is stored in separate, discontiguous memory
+buffers. Those formats are identified by a separate set of FourCC codes
+and are referred to as "multi-planar formats". For example, a
+:ref:`YUV422 <V4L2-PIX-FMT-YUV422M>` frame is normally stored in one
+memory buffer, but it can also be placed in two or three separate
+buffers, with Y component in one buffer and CbCr components in another
+in the 2-planar version or with each component in its own buffer in the
+3-planar case. Those sub-buffers are referred to as "*planes*".