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

Ppmmix User Manual(0)							    Ppmmix User Manual(0)

NAME
       ppmmix - blend together two PPM images

SYNOPSIS
       ppmmix fadefactor ppmfile1 ppmfile2

DESCRIPTION
       This program is part of Netpbm(1)

       ppmmix reads two PPM images as input and mixes them together using the specified fade fac-
       tor.  The fade factor may be in the range from 0.0 (only ppmfile1's  image  data)  to  1.0
       (only  ppmfile2's  image  data).  Anything in between specifies a smooth blend between the
       two images.

       The two images must have the same dimensions and the same  maxval.   Before  Netpbm  10.54
       (March 2011), they must also have the same type (PBM/PGM/PPM).

       The  fade  factor  is  applied to brightness, not light intensity.  That means for example
       that if you have a series of images you generated using ppmmix of  a  black  and  a  white
       image  with  a  linearly  increasing  fade  factor, you will see an image getting linearly
       brighter, but the light intensity will increase faster at the end.   That  is  because  it
       requires more intensity change at the bright end of the scale than at the dark end for the
       human eye to perceive the same brightness change.  This also means that	if  the  original
       images  aren't  all one color, the mixed image is distorted, since the intensity relation-
       ship between pixels is different from the original image.

       pamcomp is a more general alternative.  It allows you to mix images of different size  and
       to  have the fade factor vary throughout the image (through the use of an alpha mask).  It
       does not have the same-maxval and same-type restrictions.  It mixes light  intensity,  not
       brightness.

SEE ALSO
       pamcomp(1) , ppm(1)

AUTHOR
       Copyright (C) 1993 by Frank Neumann

netpbm documentation			  23 March 2010 		    Ppmmix User Manual(0)