How to use Imagick to merge and mask images?

Question

I know very little of image processing and even less of the terminology used, so please bear with me.

Basically, I want to merge two images together where one of them will act as a mask. That image looks something like this:

Where the blue and yellow background are both transparent in reality.

This image is being used as a mask for regular photo's. Parts of the photo that 'stick out' of the circle need to be 'cropped' (be made invisible) while the inside remains visible.
So everything that comes in the blue area is invisible, everything in the yellow area is visible.

I honestly have no clue how to go about it so any help would be greatly appreciated!

Edit:
I use the API version of Imagick, not the commandline version

Edit:
To get a feel of what I want to achieve, here is an example.

The input images are thus:

This is the mask image, always the same

This is an example of a picture, dynamic

This is what the end result should look like

Answer 1

So, finally, this should do what you need:

Original image:

Opacity mask:

Overlay:

Output:

The code:

<?php
$base = new Imagick('U0R4F.png');
$mask = new Imagick('mask.png');
$over = new Imagick('3ulkM.png');

// Setting same size for all images
$base->resizeImage(274, 275, Imagick::FILTER_LANCZOS, 1);

// Copy opacity mask
$base->compositeImage($mask, Imagick::COMPOSITE_DSTIN, 0, 0, Imagick::CHANNEL_ALPHA);

// Add overlay
$base->compositeImage($over, Imagick::COMPOSITE_DEFAULT, 0, 0);

$base->writeImage('output.png');
header("Content-Type: image/png");

echo $base;
?>

I hope it's right now! Note: In your example it looks like you downscaled the base image, which I didn't (my goal is just to show how the masking is done).

Answer 2

Did you try this solution here as described by : https://stackoverflow.com/a/2351173/1093649 ?

Run this in your server (with the right image names!), and let us know, thanks.

nb : credits go to jspash

Answer 3

http://www.imagemagick.org/Usage/compose/#dstin should do the trick, but you need to use images with alpha channels (that shouldn't be a problem).

Edit: in PHP you have to pass it (imagick::COMPOSITE_DSTIN) as a parameter in compositeimage. Other filters in Composite Operator Constants may also be useful to you.

Answer 4

This type of masking is exampled using a number of different techniques in ImageMagick Examples, Thumbnails, Mask and Paint http://www.imagemagick.org/Usage/thumbnails/#mask_paint

Be warned however that the masking and the edges of the overlay image SHOULD NOT MATCH this is important or you may get problems with edge aliasing effects that is best avoided.

Extracting an alpha mask of the ring, can be done using morphology operators to thin it down to a centerline can be used to generate a mask for any random 'ring' shape. ImageMagick Examples, Skeletons by Thinning, and Pruning http://www.imagemagick.org/Usage/morphology/#thinning_skeleton

Anthony Thyssen Web Master for ImageMagick Examples, and Developer for ImageMagick

PS: nice photo from Elfling