CentOS 5.1

GNU/Linux	CentOS 5.1
	pammasksharpen(1)

pammasksharpen

Updated: 14 June 2006
Table Of Contents

NAME

pammasksharpen - Sharpen an image via an unsharp mask

SYNOPSIS

pammasksharpen [-sharpness=realnum [-threshold=realnum maskfile [inputfile]

All options can be abbreviated to their shortest unique prefix. You may use
two hyphens instead of one. You may separate an option name and its value
with white space instead of an equals sign.

EXAMPLES

pamgauss 5 5 -sigma=.7 -tupletype=GRAYSCALE | pamtopnm >gauss.pgm
pnmconvol gauss.pgm myimage.ppm >blurred.ppm
pammasksharpen blurred.ppm myimage.ppm >sharpened.ppm

DESCRIPTION

This program is part of Netpbm.

pammasksharpen reads a Netpbm image as input and produces a sharpened
version of it, in the same format, as output. It does this via an unsharp
mask, which you supply as another Netpbm image.

An unsharp mask is generally a blurred version of the original image. The
sharpening computation is this: Calculate the "edgeness" of a sample in the
input image as the signed difference between the sample value and the
corresponding sample in the unsharp mask. This tells how different the pixel
is from its neighbors. Add a multiple of the edgeness to the original sample
to get the corresponding output sample. Clip as necessary. This causes
pixels that are brighter than their neighbors to get even brighter, while
pixels that are dimmer than their neighbors get even dimmer. This makes
edges -- places where pixel values change quickly in space -- stand out
more.

The unsharp mask must be the same dimensions and have the same maxval as the
input image.

The Unsharp Mask

You usually create the unsharp mask as a gaussian blur of the original
image, which you can do using pamgauss and pnmconvol as in the example
above. The convolution kernel you use with pnmconvol is normally a square
with side length an odd number of pixels.

When you create an unsharp mask like this, you will have to choose the side
length of the convolution kernel. That length implements the parameter of
unsharp mask sharpening usually known as "radius." In particular, a radius
of R pixels corresponds to a convolution kernel 2R+1 pixels on a side.

Radius is a very important parameter; you can ruin an image with a radius
too large. You can safely use the highest radius with an inanimate object,
while a human face demands the least. Landscapes fall in between. But it
really depends on the size of the details. Fine detail needs a smaller
radius, or else you may obliterate tiny detail of the same size as the
Radius width. A large image often has larger detail (more pixels involved),
so can use a larger radius. Radius and sharpness (see -sharpness option)
interact: reducing one allows you to increase the other.

OPTIONS

-sharpness=realnum
This specifies the magnitude of the sharpening. It is the multiple of
edgeness that gets added to each sample as described above.
realnum is a nonnegative real decimal number. Zero means no
sharpening at all.
This parameter is known as "amount" in ImageMagick.
The default is 1.0.
This option was new in Netpbm 10.30 (October 2005). Before that, the
sharpness was always 1.0.
-sharpness=realnum
This minimum amount of edgeness that will be considered edgeness at
all. i.e. if the magnitude of the edgeness is less than this,
pammasksharpen will treat the edgeness as zero.
A nonzero value may be necessary here to avoid speckling in smooth
areas.
This is a fraction of the maxval (so it is in the range [0, 1.0]).
The default is 0.
This option was new in Netpbm 10.34 (June 2006).

GNU/Linux man pages

Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :

ISBN : 978-2-7460-9712-4
EAN : 9782746097124
(Editions ENI)

GNU/Linux

pammasksharpen(1)