ppmtoyuv



Ppmtoyuv User Manual(0)                                Ppmtoyuv User Manual(0)




NAME

       ppmtoyuv - convert a PPM image to an Abekas YUV file



SYNOPSIS

       ppmtoyuv [ppmfile]



DESCRIPTION

       This program is part of Netpbm(1).

       ppmtoyuv  reads a PPM image as input and produces an Abekas YUV file as
       output.

       The output file contains a raster of four byte YUV codes, each uniquely
       associated  with two side-by-side pixels in the image.  The raster con-
       tains rows in order from top to bottom, and  within  each  row  columns
       from left to right.  So the output file size in bytes is twice the num-
       ber of pixels in the image.

       Each YUV code is associated with two pixels from the input  image  that
       we  will  call the left pixel and the right pixel.  The 2nd byte of the
       code is the Y value of the left pixel.  The 4th byte of the code is the
       Y  value of the right pixel.  The 1st byte of the code is an average of
       the U value of the pixel to the left of the left pixel, the left pixel,
       and  the right pixel.  The 3rd byte of the code is analogous for V val-
       ues.  These averages are weighted arithmetic means where the left pixel
       is weighted double what the other two pixels are weighted.

       This  format is reminiscent of but rather different from the common YUV
       4:2:0 format (aka YUV 420) and the similar YUV 4:4:4,  YUV  4:2:2,  YUV
       4:1:1,  YUV 4:1:1s, and YUV 4:1:0.  In YUV 4:2:0, the raster is differ-
       ent for even numbered lines and odd numbered lines.  On  even  numbered
       lines,  there are twice as many bits for Y of each pixel as for U or V.
       On odd numbered lines, there are the same number of bits for  Y  as  on
       even numbered lines, but no bits at all for U and V.



SEE ALSO

       yuvtoppm(1), ppmtoeyuv(1), ppmtoyuvsplit(1), ppm(1)



AUTHOR

       Marc  Boucher  marc@PostImage.COM, based on Example Conversion Program,
       A60/A64 Digital Video Interface Manual, page 69.

       Copyright (C) 1991 by DHD PostImage Inc.

       Copyright (C) 1987 by Abekas Video Systems Inc.



netpbm documentation             06 June 2005          Ppmtoyuv User Manual(0)

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