Unix/Linux Go Back    


CentOS 7.0 - man page for pamtohdiff (centos section 0)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


Pamtohdiff User Manual(0)						Pamtohdiff User Manual(0)

NAME
       pamtohdiff - convert PAM image to horizontal difference image

SYNOPSIS
       pamtohdiff [pamfile] [-verbose]

       Minimum	unique	abbreviation of option is acceptable.  You may use double hyphens instead
       of single hyphens to denote options.  You may use white space in place of the equals  sign
       to separate an option name from its value.

DESCRIPTION
       This program is part of Netpbm(1)

       pamtohdiff  takes a PAM (or PNM) image as input and produced a horizontal difference image
       version of it as output.  A horizontal difference image is one where the samples  in  each
       row  indicate  the  difference between the sample value in the corresponding sample of the
       input image and the sample directly above it (in the previous row)  in  the  input  image.
       The  horizontal	difference  image has the property that if a row of the original image is
       identical to the row above it over a long extent, the corresponding row in the  horizontal
       difference image will contain all zeroes.  That makes it compress better than the original
       image.

       Because the horizontal difference samples can be positive or negative, but PAM samples are
       unsigned  integers,  the  samples in the horizontal difference image PAM are defined to be
       the difference modulus the range of the input (maxval + 1).  This doesn't lose any  infor-
       mation,	as  it	might seem, because: of the two differences that could result in the same
       pamtohdiff output value (e.g. if maxval is 99, +20 and -80 would both result  in  "20"  in
       the output), only one is possible in context and the other would result, when reconstruct-
       ing the original image, in a value less than 0 or greater than maxval.

       Before the modulus operation, the values pamtohdiff computes are also biased by	half  the
       maxval.	This is to make the results easier to inspect visually.  Because of the bias, you
       can display the pamtohdiff output as if it were a PNM image.  As long as none of your dif-
       ferences  are more than half the maxval, large negative differences show up as dark spots,
       smaller negative differences are lighter, zero differences are medium intensity, and posi-
       tive  differences  are  light.  If you want this to work even for images that have differ-
       ences that exceed half the maxval, just use ppmdim 50 on the  original  image.	To  avoid
       losing information, though, do a pamdepth to double the maxval first.

       Note  that because of the transfer function just described, a difference of zero, which is
       most common, is represented by a PAM sample value in the output of one half the maxval.

       The output PAM has a tuple type of "hdiff".

       You can use hdifftopam to recover the original image from a  horizontal	difference  image
       PAM.

SEE ALSO
       hdifftopam(1) , pamdepth(1) ,

AUTHOR
       Bryan Henderson

netpbm documentation			  15 April 2002 		Pamtohdiff User Manual(0)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 06:39 PM.