y4mtopnm.1

Motion JPEG编解码器源代码

.\" 
.TH "y4mtopnm" "1" "28 April 2004" "MJPEG Linux Square" "MJPEG tools manual"
.SH "NAME"
y4mtopnm \- Convert a YUV4MPEG2 stream to PNM images

.SH "SYNOPSIS"
.B y4mtopnm
.RI [ options ]

.SH "DESCRIPTION"
\fBy4mtopnm\fP converts a YUV4MPEG2 stream into a sequence
of raw PPM, PGM, or PAM images.  (Technically, "pnm" comprises the PPM, PGM and
PBM formats.  PAM is a fourth format, which can effectively contain any of 
the other three, and more.)

Output is to stdout (but feel free to have the shell redirect to a file).

Input is read from stdin, like all other YUV4MPEG2 filters and tools.
YUV4MPEG2 streams contain frames using the Y'CbCr colorspace
(ITU-R BT.601).  For 4:4:4 (color) streams, \fBy4mtopnm\fP will convert
each pixel to the usual R'G'B' colorspace used for computer graphics,
and produce PPM images.  "MONO" (luma-only) streams will be converted
to full-range [0,255] grayscale and output as PGM images.

YUV4MPEG2 streams may (often!) have subsampled chroma planes, but
\fBy4mtopnm\fP will not process them.  Subsampled streams will need to
be converted to 4:4:4 using a tool such as \fBy4mscaler\fP. 

If \fBy4mtopnm\fP is given a "444ALPHA" stream (4:4:4 video with
an 8-bit alpha channel), the results depend on whether or not the "-P" option
is specified.  With "-P", it will produce PAM images with a TUPLTYPE of
RGB_ALPHA, containing both color and alpha channel data.
Without "-P", it will produce pairs of PPM and PGM images: 
a PPM for the color pixels followed by a PGM for the alpha channel data.
(Such a sequence of interspersed PPM and PGM images cannot be later
re-processed by \fBpnmtoy4m\fP.  This feature is mostly for quick and
easy stream debugging.)

If multiple output images are generated, they are simply output one after
another.  If you want to turn such a "multi-image" stream/file into
individual files, use \fBpnmsplit\fP.  (Some PNM filters can process
multi-image files/streams; however, many written before June 2000 will
only process the first image.)

\fBy4mtopnm\fP and \fBpnmtoy4m\fP are inverses of each other; you can
typically pipe the output of one into the other, and vice-versa (except
for the "444ALPHA" case noted above and the "mixed-mode" case noted below).
Note that the colorspace operations
can be lossy in both directions (due to range-compression and/or
quantization).  And, when converting to PNM, information on
interlacing and sample aspect ratio of a stream
is lost (but can be reconstructed by supplying command-line arguments to
\fBpnmtoy4m\fP).


.SH "OPTIONS"
\fBy4mtopnm\fP accepts the following options:

.TP 5
.BI \-P
Produce PAM format output, instead of PPM and/or PGM.  PAM can encode a
superset of PNM, but is not yet understood by as many graphics programs.
(Indeed, surprisingly few of the NetPBM tools seem to understand it.)
.TP 5
.BI \-D
Produce a separate output image for each field of each frame.
(Otherwise, a single image per frame, containing two interleaved fields,
is created.)

If the input stream is interlaced, the field-images are output in temporal
order, i.e. the first image of a bottom-field-first stream will be the
bottom-field.
If the stream is progressive or has "mixed-mode" interlacing, then the
temporal order is ambiguous, and the top-field will always be output first.

Note that it will \fInot\fP be possible to later use \fBpnmtoy4m\fP to
reconstruct a "mixed-mode" stream from a sequence of PNM/PAM images.
.TP 5
.BI \-v " [0,1,2]"
Set verbosity level.  
 0 = warnings and errors only.
 1 = add informative messages, too.
 2 = add chatty debugging message, too.

.SH "EXAMPLES"
.hw y4mtopnm pnmsplit lav2yuv
To turn the first 15 frames of an (MJPEG or DV) AVI file into individual
PPM files:

.RS 5
lav2yuv -f 15 your-video.avi | y4mscaler -O chromass=444 | y4mtopnm | pnmsplit - "your-video-%d.ppm"
.RE

.SH "AUTHOR"
This manual page was written by Matt Marjanovic.
.br 
If you have questions, remarks, problems or you just want to contact
the developers, the main mailing list for the MJPEG\-tools is:
  \fImjpeg\[e-mail]\fP

.TP 
For more info, see our website at
.I http://mjpeg.sourceforge.net/

.SH "SEE ALSO"
.BR pam (5),
.BR pgm (5),
.BR pnm (5),
.BR ppm (5),
.BR pnmtoy4m (1),
.BR mjpegtools (1),
.BR mpeg2enc (1),
.BR lav2yuv (1),
.BR pnmsplit (1),
.BR y4mscaler (1)