Ubuntu Manpage: y4mtopnm - Convert a YUV4MPEG2 stream to PNM images

Provided by: mjpegtools_2.1.0+debian-6build1_amd64

NAME

       y4mtopnm - Convert a YUV4MPEG2 stream to PNM images

SYNOPSIS

       y4mtopnm [options]

DESCRIPTION

y4mtopnm 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, 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 pnmtoy4m. 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).

OPTIONS

       y4mtopnm 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 ambiguous, and the  top-field  will  always  be
            output first.

            Note  that it will not be possible to later use pnmtoy4m to reconstruct 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 essentially just a reformatting/permutation of the original data from the input
            stream into a PGM image container.  All the other command-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 individual PPM files:

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

AUTHOR