Re: [Gimp-user] gradient

[Jeff Trefftzs]

Indira asked:
> if I have an image and I want to use the colors of that image, how do i
> make a custom gradient?

First method (long and tedious):

Use the gradient editor, picking colors from the image and
dropping them into the gradient as described in the
GimpUsersManual_2ndEdition.pdf.

An easier method:

I have wondered about this myself in connection with palettes,
which often have a nicely selected set of colors already
available. I have built a pair of little perl procs to (1) sort
a palette by value, hue, saturation, or hsv_value,
and (2) create a gradient from a palette. In the hope that
these may answer your need, I have attached them.

Caveats: They are NOT documented very well. Consider them
beta, at best. I have used them successfully myself, but YMMV.
Particularly on pal2grad.pl, read the code. You can set the number of steps in the resulting gradient.


--
--Jeff
Jeff Trefftzs <[EMAIL PROTECTED]>
http://www.tcsn.net/trefftzs Home Page
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#!/usr/local/bin/perl

#  pal2grad.pl - convert a GIMP palette to a gradient.

use strict;
use vars qw($opt_r $opt_b $opt_n);
use Getopt::Std;

# parse command line arguments
getopts('rbn:');


if ($ARGV < 0) {
    die "$ARGV[0]:  Can't find a file to process\n";
}

my @PALETTE = ();
my @GRADIENT = ();

while (<>) {
    if(/^[^0-9 ]/) {            # skip comments and headers
        next;
    }
    push @PALETTE, $_;
}

my $STEPS = $#PALETTE;          # how many entries in the palette

my $count = (defined $opt_n) ? $opt_n : $STEPS;

my $width = 1.0/$count;         # width of one segment
my $demi = $width/2;            # distance to midpoint
my @oldcolor = split(/\s/, $PALETTE[0], 3);

my $alpha = 1.0;

for (my $i = 1; $i <= $count; $i++) {
    my $index = $i *  ($STEPS/$count);
    my ($red, $green, $blue) = split(/\s/, $PALETTE[$index], 3);

#    printf stderr "red=$red, green=$green, blue=$blue\n";

    my ($start, $middle, $end) = (($i -1) * $width,
                                  $i * $width - $demi,
                                  $i * $width);
    if (defined $opt_r) {
        $start = 1.0 - $end;
        $middle = 1.0 - $middle;
        $end = 1.0 - (($i - 1) * $width);
    }

    my $grad_entry = sprintf ("%f %f %f %f %f %f %f %f %f %f %f 
%d %d\n",
                              $start,
                              $middle,
                              $end,

                              $oldcolor[0]/255, # starting red
                              $oldcolor[1]/255, # starting green
                              $oldcolor[2]/255, # starting blue
                              $alpha,

                              $red/255, # ending red
                              $green/255, # ending green
                              $blue/255, # ending blue
                              $alpha, # Opacity - constant for now

                              0, # linear blend
                              0 # rgb coloring
                              );

    if (!(defined $opt_r)) {
        push @GRADIENT, $grad_entry;
    } else {
        unshift @GRADIENT, $grad_entry;
    }
    @oldcolor = ($red, $green, $blue);
}

print "GIMP Gradient\n";
printf "%d\n", $count;

print @GRADIENT;