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.