in reply to Pixel setting oddity - Image:Magick

In  $img_gry->Set('pixel[$col,$row]' => 'rgb($sub_red, $sub_green, $sub_blue )'); the single quotes prevent interpolation which means Image::Magick is given the strings '$col', and '$row' instead of the values you expect. I didn't read the documentation to see if anything else is wrong, but this does look highly suspicious. Aren't you getting any warnings for that? I'm surprised Image::Magick doesn't complain about the invalid input.

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Re^2: Pixel setting oddity - Image:Magick
by afoken (Chancellor) on May 11, 2015 at 12:30 UTC
    Aren't you getting any warnings for that? I'm surprised Image::Magick doesn't complain about the invalid input.

    The posted code has a bare string eval without any error checks ($@), so most errors will be silent. Also, Image::Magick requires a lot of manual error checks because it does not use perl's exception mechanism (i.e. die), but instead requires checking return values (as in C). This is documented in http://www.imagemagick.org/script/perl-magick.php#exceptions. The posted code lacks those checks, too.

    Alexander

    --
    Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
[reply]

      Thanks for the info on exception handling with Image::Magick!

      And yes, merrymonk fails to check $@ after the eval, but there wouldn't have been a warning there since this actually works (as in this case the variables are actually in a double quote context). And on the topic of safety and error checking, it does look like the code is not run under strict and warnings ; which would have done nothing for this particular case, but are still very helpful safety nets.

[reply]
        Thank you for that explanation. Indeed is was the single quotes that were stopping it working. When I changed these to 4 double quotes all was well!
[reply]

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