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y4munsharp(1)


NAME

   y4munsharp - Unsharp filter for YUV4MPEG2 streams

SYNOPSIS

   y4munsharp [options]

DESCRIPTION

   y4munsharp  is  an  implementation  of  the   GIMP  unsharp  filter for
   YUV4MPEG2 streams.  The usual 3 parameters for unshap  mask  processing
   (radius,  amount  and threshold) are specified on the command line.  By
   default only the Y' (luma) component is processed  although  processing
   of  the CbCr (chroma) may be requested by a commandline option.  Output
   must be either to a pipe or a file, leaving stdout as a  terminal  will
   elicit an error and the program will exit.

OPTIONS

   y4munsharp accepts the following options:

   -v num
        Set  verbosity  level (0 = quiet, 1 = normal, 2 = debug) (default:
        1)

   -h   Print a suage summary and exit

   -L radius,amount,threshold
        Y' (luma) unsharp parameters.  The radius  and  amount"  arguments
        are floating point numbers.  The threshold argument is an integer.
        (default:  3.0,0.3,4)  -C  radius,amount,threshold  CbCr  (chroma)
        unsharp  parameters.   The  chroma  is  not  processed unless this
        option is given.  Arguments are the same type as for the -L option
        above.  (default: none)

   -N   Filtering  can  produce  output outside the 16 to 240 range for Y'
        and 16 to 235 for CbCr.  By default values outside the legal range
        are  clipped/cored  (values  over  240  for  Y' are set to 240 for
        example).  Using -N the limits 0 and 255 are used instead.

EXAMPLES

   A mild setting:
   y4munsharp -L 2.0,0.3,0

   An aggressive setting:
   y4munsharp -L 5.0,0.5,0

NOTES

   The radius, amount, threshold parameters have the same meaning  as  the
   GIMP's  unsharp  plugin.   This  means you can use the GIMP on selected
   frame still images to determine suitable settings for y4munsharp.   The
   key  thing to remember is to be subtle - you just barely want to notice
   the sharpening effect.  If the effect is obvious ("jumps out  at  you")
   then the parameters are set too aggressively.

   The  chroma is not processed for a several reasons:  1) The eye is much
   more sensitive to changes in brightness,   2)  the  chroma  is  usually
   subsampled and doesn't contribute much to the perceived sharpness of an
   image - so not processing the chroma  provides  a  boost  in  speed  of
   processing  the image, and 3) possible artifacting - changes in Y' just
   make an image brighter/darker but  changes  in  Cb  or  Cr  can  change
   colors and possibly lead to shifts in hue.  Use the -C option to enable
   processing of the chroma planes.

BUGS

   Only the 3 plane YUV4MPEG2 formats are supported.

   Only progressive, top field first  or  bottom  field  first  interlaced
   streams  are  handled.   The  mixed  interlaced  stream  format  is not
   supported.



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