Convert a YUV4MPEG2 stream to PNM images
see also :
pnmtoy4m - mpeg2enc - lav2yuv - pnmsplit
add an example, a script, a trick and tips
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"
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
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.
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
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.)
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.)
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
accepts the following options:
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.)
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.
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.
Set verbosity level.
0 = warnings and errors only.
1 = add informative messages, too.
2 = add chatty debugging message, too.
pgm, pnm, ppm,
pnmtoy4m , mjpegtools,
mpeg2enc , lav2yuv , pnmsplit ,
page was written by Matt Marjanovic.
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