Section: MJPEG tools manual (1)
Updated: 28 April 2004
pnmtoy4m - Convert PNM/PAM images to YUV4MPEG2 stream
[ filename ]
converts one or more raw PPM, PGM, PBM, or PAM images into a
YUV4MPEG2 stream ready for further processing by other video tools.
These three (or four) image formats are collectively referred to
as "PNM images".
Output is to stdout to facilitate piping to other MJPEG tools.
The size of the output frame(s) is determined from the (first) input image.
Input is a 'raw' format PNM image, read from stdin or from the optional
filename. The input may contain multiple PNM images concatenated together;
pnmtoy4m will read and process them sequentially. All images must have
identical size and format. Input images can be interpreted as whole
progressive frames, pairs of interleaved fields, or as sequential fields
(read in pairs of images) to be output as either interlaced or progressive
PPM and PGM images must have 8 bits per channel (i.e. 'maxval' must be 255).
PPM input images should be in the usual R'G'B' colorspace. They are converted
to the Y'CbCr colorspace (ITU-R BT.601) before being output to a "4:4:4"
(non-subsampled) YUV4MPEG2 stream. If chroma subsampling is required
(e.g. to 4:2:0 for MPEG), the output should be further piped through a
program such as y4mscaler.
PGM images should be in the standard full-range ([0,255])
grayscale colorspace. PGM and PBM images will be converted to BT.601 luma
and output as "MONO" (luma-only) YUV4MPEG2 streams.
The PAM format is a newer superset of the PNM formats; the precise contents
of a PAM image is defined by the TUPLTYPE header tag. pnmtoy4m
handles TUPLTYPE "GRAYSCALE" as PGM, "RGB" as PPM, and "RGB_ALPHA" as
PPM with an 8-bit alpha channel. (The alpha channel is converted to
BT.601 luma as is appropriate for YUV4MPEG2 streams.)
pnmtoy4m and y4mtopnm are inverses of each other; you can
pipe the output of one into the other, and vice-versa. Note that the
colorspace operations are lossy in both directions. And,
when converting to PNM, information on interlacing and sample aspect ratio
is lost (but can be reconstructed by supplying command-line arguments to
accepts the following options:
- -o num
Frame offset: skip output of the first 'num' frames. (default: 0)
- -n num
Output a total of 'num' output frames. Use '0' to specify all frames.
Interpret data as being BGR rather than RGB.
Repeat last input frame until output is complete. If '-n 0' is also specified,
last input frame will be repeated forever.
- -D x
Treat each PNM image as a single (de-interleaved) field instead of a full
frame. The argument specifies the interpretation:
t - the first image is a top-field
b - the first image is a bottom-field
With this option, two input images will be required per output frame.
Be careful: mismatched "-I" and "-D" options can invert the temporal or
spatial order of the fields (or both).
- -F n:d
Set framerate encoded in output stream, as an exact integer ratio.
(default: 30000:1001) Common rates are:
24000:1001 - NTSC 3:2 pulldown converted film
24:1 - native film
25:1 - PAL/SECAM
30000:1001 - NTSC video
50:1 - PAL field rate
60000:1001 - NTSC field rate
- -A n:d
Set pixel aspect ratio encoded in output stream, as an exact integer ratio.
(default: 1:1) Common ratios are:
1:1 - square pixels (computer graphics)
10:11 - CCIR-601 NTSC
59:54 - CCIR-601 PAL
- -I x
Set the output interlacing mode, encoded in the output stream.
(Default is to match "-D" if given, or 'p' if not.)
p - progressive, non-interlaced
t - top/upper-field-first interlaced
b - bottom/lower-field-first interlaced
- -v [0,1,2]
Set verbosity level.
0 = warnings and errors only.
1 = add informative messages, too.
2 = add chatty debugging message, too.
To convert a file containing a single PPM file into a stream of 15
pnmtoy4m -n 15 -r some-image.ppm
To convert a series of Targa format images (in the current directory)
to a YUV4MPEG2 stream displayed by yuvplay:
ls *.tga | xargs -n1 tgatoppm | pnmtoy4m | yuvplay
This manual page was written by Matt Marjanovic.
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