PDL::ImageRGB (3)

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NAME

PDL::ImageRGB -- some utility functions for RGB image data handling

DESCRIPTION

Collection of a few commonly used routines involved in handling of palette and grayscale images. Not much more than a start. Should be a good place to exercise some of the thread/map/clump stuff.

Other stuff that should/could go here:

*

color space conversion

*

common image filters

*

image rebinning

SYNOPSIS

 use PDL::ImageRGB;

FUNCTIONS

cquant

quantize and reduce colours in 8-bit images

    ($out, $lut) = cquant($image [,$ncols]);

This function does color reduction for <=8bit displays and accepts 8bit

and 8bit palette images. It does this through an interface to the ppm_quant routine from the pbmplus package that implements the median cut routine which intellegently selects the 'best' colors to represent your image on a <= 8bit display (based on the median cut algorithm). Optional args: $ncols sets the maximum nunmber of colours used for the output image (defaults to 256). There are images where a different color reduction scheme gives better results (it seems this is true for images containing large areas with very smoothly changing colours).

Returns a list containing the new palette image (type PDL_Byte) and the

colormap.

interlrgb

Make an image from a palette image and its lookup table.

    $rgb = $palette_im->interlrgb($lut)

Input should be of an integer type and the lookup table (3,x,...). Will perform the lookup for any N-dimensional input pdl (i.e. 0D, 1D, 2D, ...). Uses the index command but will not dataflow by default. If you want it to dataflow the dataflow_forward flag must be set in the $lut piddle (you can do that by saying $lut->set_dataflow_f(1)).

rgbtogr

Converts an image to a grey scale using standard transform

   $gr = $rgb->rgbtogr

Performs a conversion of an

input image (3,x,....) to a greyscale image (x,.....) using standard formula:

   Grey = 0.301 R + 0.586 G + 0.113 B

bytescl

Scales a pdl into a specified data range (default 0-255)

        $scale = $im->bytescl([$top])

By default $top=255, otherwise you have to give the desired top value as an argument to "bytescl". Normally "bytescl" doesn't rescale data that fits already in the bounds 0..$top (it only does the type conversion if required). If you want to force it to rescale so that the max of the output is at $top and the min at 0 you give a negative $top value to indicate this.

BUGS

This package doesn't yet contain enough useful functions!

AUTHOR

Copyright 1997 Christian Soeller <c.soeller@auckland.ac.nz> All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation under certain conditions. For details, see the file in the distribution. If this file is separated from the distribution, the copyright notice should be included in the file.