.TH pamblend 1 "21 May 2004"
.IX pamblend
.SH NAME
pamblend - simulate long or multiple exposures
.SH SYNOPSIS
.B pamblend
.BR -closest | -average | -furthest | -brightest | -darkest
.I pnmfile1 pnmfile2 pnmfile3 [ pnmfile4 ... ]
.SH DESCRIPTION
Reads all portable anymaps as input (which must be the same width and
height, and should be of the same subject, from a fixed camera, under
very similar lighting conditions) and simulates long or multiple
exposures by either removing or enhancing transient elements; produces a
portable anymap as output.
.PP
Considers equivalent pixels in all input images and selects or
generates one for output based on the program options.
.SH OPTIONS
.TP
.B -closest
Select the colour is closest in colourspace to most other pixels. Use
this to remove unwanted transient elements from a static scene, such
as people in front of a landscape. For closest results, use as many
exposures as possible.
.TP
.B -furthest
Select the one that is furthest in colourspace from
most other pixels. Use this to highlight transient elements in a
static scene, such as a race-car on a track or a rising moon. For closest
results, select exposures taken at similar time intervals.
.TP
.B -average
As -closest, but select a colour which is the average of those in all
images. This will produce misty, ghostly effects, similar to
.B ppmmix(1)
or
.B pamcomp(1)
.TP
.B -brightest
Select the brightest pixel.
.TP
.B -darkest
Select the darkest pixel.
.SH NOTES
It is important to use images taken from a fixed camera so that
non-transient parts of the scene are the same in each image. Slight
camera movements between images can be corrected by using
.B pamalign(1).
.PP
If possible with your camera, lock focus and exposure between shots
and avoid taking pictures under rapidly changing lighting conditions
(such as moving cloud).
.SH EXAMPLE
If you have five images of a cathedral with people milling about in
front of it, eliminate the people as follows:
.PP
pamblend -closest cath1.ppm cath2.ppm cath3.ppm cath4.ppm cath5.ppm > cath-blended.ppm
.SH BUGS
Large movements or completely different scenes will produce
results that are at closest amusing, and at worst grotesque.
.PP
When only a few images are available, the laws of chance often result
in small parts of the image being obscured by different transient
elements in each image. These parts must be corrected by hand.
.SH "SEE ALSO"
pamalign(1), pnmarith(1), pamcomp(1), ppmmix(1), pnm(5)
.SH AUTHOR
Copyright (C) 2004, Fraser McCrossan
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