y4mtopnm(1) MJPEG tools manual y4mtopnm(1)NAMEy4mtopnm - Convert a YUV4MPEG2 stream to PNM images
SYNOPSISy4mtopnm [options]
DESCRIPTIONy4mtopnm converts a YUV4MPEG2 stream into a sequence of raw PPM, PGM,
or PAM images. (Technically, "pnm" comprises the PPM, PGM and PBM for‐
mats. 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, y4mtopnm 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
y4mtopnm will not process them (except in the special 'flatten' mode;
see below). Subsampled streams will need to be converted to 4:4:4
using a tool such as y4mscaler.
If y4mtopnm 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 pnm‐
toy4m. 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 pnmsplit. (Some PNM filters can process
multi-image files/streams; however, many written before June 2000 will
only process the first image.)
y4mtopnm and pnmtoy4m 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 pnmtoy4m).
OPTIONSy4mtopnm accepts the following options:
-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.)
-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 ambigu‐
ous, and the top-field will always be output first.
Note that it will not be possible to later use pnmtoy4m to recon‐
struct a "mixed-mode" stream from a sequence of PNM/PAM images.
-f Produce a special 'flattened' output, most useful for analyzing
and debugging streams. All the planes of a frame/field are tiled
together into an enlarged PGM (or grayscale PAM) output image as
follows:
+-----+ +-----+
4:4:4 | Y | 4:4:4 w/alpha | Y |
+-----+ +-----+
| Cb | | Cb |
+-----+ +-----+
| Cr | | Cr |
+-----+ +-----+
| A |
+-----+ +-----+
4:2:2, | Y |
4:2:0 +--+--+ +-----+--+--+
|Cb|Cr| 4:1:1 | Y |Cb|Cr|
+--+--+ +-----+--+--+
+-----+
MONO | Y |
+-----+
In this mode, any YUV4MPEG2 chroma format is accepted, but no
upsampling or colorspace conversion is performed. This is essen‐
tially just a reformatting/permutation of the original data from
the input stream into a PGM image container. All the other com‐
mand-line flags continue to have the same effect on output.
-v [0,1,2]
Set verbosity level.
0 = warnings and errors only.
1 = add informative messages, too.
2 = add chatty debugging message, too.
EXAMPLES
To turn the first 15 frames of an (MJPEG or DV) AVI file into individ‐
ual PPM files:
lav2yuv -f 15 your-video.avi | y4mscaler -O chromass=444 |
y4mtopnm | pnmsplit - "your-video-%d.ppm"
AUTHOR
This manual page was written by Matt Marjanovic.
If you have questions, remarks, problems or you just want to contact
the developers, the main mailing list for the MJPEG-tools is:
mjpeg-users@lists.sourceforge.net
For more info, see our website at
http://mjpeg.sourceforge.net/
SEE ALSOpam(5), pgm(5), pnm(5), ppm(5), pnmtoy4m(1), mjpegtools(1),
mpeg2enc(1), lav2yuv(1), pnmsplit(1), y4mscaler(1)MJPEG Linux Square 28 April 2004 y4mtopnm(1)
