\
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.TH "Pgmdeshadow User Manual" 0 "06 July 2006" "netpbm documentation"
.PP
.SH NAME

pgmdeshadow - Deshadow a PGM image

.UN synopsis
.SH SYNOPSIS

\fBpgmdeshadow\fP

[\fIpnmfile\fP]


.UN description
.SH DESCRIPTION
.PP
This program is part of
.BR Netpbm (1)
.
.PP
\fBpgmdeshadow\fP removes gray shadows from an image.  This is
useful for an image containing text, such as a scanned book pages,
where a shadow typically appears near the book crease or near one side
of the image.  \fBpgmdeshadow\fP recognizes a gray shadow as an area
of smoothly changing color, starting from the outer edges of the
image.  The program uses a simple image reconstruction algorithm to
determine the local shadow gray level, then divides each pixel's gray
level by the local shadow gray level.
.PP
The algorithm is the 'fast hybrid grayscale reruction'
algorithm from Luc Vincent, "Morphological Grayscale Reruction in
Image Analysis: Applications and Efficient Algorithms.


.UN options
.SH OPTIONS
.PP
None.

.UN references
.SH REFERENCES



.IP \(bu
Luc Vincent, 'Morphological Grayscale Reruction in Image
Analysis: Applications and Efficient Algorithms,' IEEE
Transactions on Image Processing, vol. 2, no. 2, April 1993,
pp. 176-201.




.UN seealso
.SH SEE ALSO
.BR ppmshadow (1)
,
.BR pgm (5)


.UN history
.SH HISTORY
.PP
\fBpgmdeshadow\fP was added to Netpbm in Version 10.35 (August 2006).