在比较API中将PerlMagick与Fuzz参数一起使用

Question

I am trying to use perlmagick to compare 2 images. It works perfectly fine for most of the cases, but if there is slight difference in pixels then it is counted as error. If I use compare command provided by ImageMagick then I can specify fuzz parameter which will treat pixels in the given distance as same.

I tried using fuzz option in compare api as suggested in documentation but it's not working. http://www.imagemagick.org/script/perl-magick.php

$Difference = $orgImage->Compare( image => $secondImage, metric => 'RMSE', fuzz => '100', channel => 'ALL' );

Thanks !

Answer 1

This is a known issue in PerlMagick which hasn't been fixed since its discovery in 2009, it would seem that the Compare() function internally uses an equality operation rather than a comparison operation. Maybe call the CLI utility from in your perl script?

use strict;
use warnings;

my $difference = `compare -metric RMSE -fuzz 15% first.png second.png null: 2>&1`;
my $diffAmount = $difference =~ m/\([\d.]*\)/;

if ($diffAmount == 0) {
    print "Yay\n";
}

Answer 2

You can work around the issue of fuzz not working by extracting error data from the difference image. Here is a routine I have used in comparison tests.

sub cmp_image {
    my ( $result_img, $expect_img, $max_error, $test_name ) = @_;

    my $difference_img = $expect_img->Compare( 
       image => $result_img,
       metric=>'rmse' );

    ok( $difference_img->Get('error') < $max_error, $test_name )
        or diag "Error metric: " . $difference_img->Get('error');
}

Unfortunately, this approach does not help you if you want to view the locations of errors, as even smallest differences between the images will be drawn in $difference_img .