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phpimageimage-processingimagick

Subtract two images to leave result - PHP

I have two images (both maps) one is a plain map and one is a map that had pins on it.

Image one

Image One

Image Two

Image Two

I'm trying to subtract them from each other so I'm left with just the pins as a transparent png.

I've had some success with this and have managed to get the pins as their own image, the problem is that the colours aren't quite right (see image 3).

Image Three

Image Three

I'm using Imagick to do this and my code is below

<?php

// load in the base image into Imagick
$imageOne = new Imagick('images/base-map.png');
$imageTwo = new Imagick('images/pins/location-7.png');

$imageOne->compositeImage($imageTwo, Imagick::COMPOSITE_DIFFERENCE, 0, 0);
$imageOne->paintTransparentImage($imageOne->getImagePixelColor(0, 0), 0, 5000);

header('Content-Type: image/png');

echo $imageOne;

Does anyone know how I can tidy/tweak this to make the colours match the original image?

Thanks!

Solution

  • I've managed to get this to work using the masking technique mentioned by Piglet and wandering-warrior and with help from this post as well

    In case anyone else needs it the code is here: 

    <?php

$base = new Imagick('images/base-map.png'); // blank map
$mask = $base; // copy of this to create the mask with
$imageTwo = new Imagick('images/pins/location-7.png'); // image with pins on it

// create the mask
$mask->compositeImage($imageTwo, Imagick::COMPOSITE_DIFFERENCE, 0, 0);
$mask->paintTransparentImage($mask->getImagePixelColor(0, 0), 0, 5000);
$mask->compositeImage($mask, Imagick::COMPOSITE_DIFFERENCE, 0, 0);

// remove the mask from the image with pins
$imageTwo->compositeImage($mask, Imagick::COMPOSITE_DSTIN, 0, 0, Imagick::CHANNEL_ALPHA);
$imageTwo->paintTransparentImage('#000', 0, 5000);

header('Content-Type: image/png');
echo $imageTwo;

    The mask looks like so mask

    and the final output like so

    enter image description here

    Hopefully this will help someone else who needs it!