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y4munsharp(1)		      MJPEG tools manual		 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 exam‐
	    ple).  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 sub‐
       sampled	and  doesn't  contribute much to the perceived sharpness of an
       image - so not processing the chroma provides a boost in speed of  pro‐
       cessing	the  image,  and  3) possible artifacting - changes in Y' just
       make an image brighter/darker but changes in Cb or Cr can change	  col‐
       ors  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 sup‐
       ported.

MJPEG Linux Square	       11 November 2004			 y4munsharp(1)

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