MATLAB: Image Blending/ Image Fusion

image processingImage Processing Toolbox

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The linked file is a PDF with 17 slides. My virus scanner did not find malware in the file, but the last security announcement of Adobe is just some hours old: http://www.adobe.com/support/security/bulletins/apsb13-22.html . I recommend to remove this link and post the formula directly.
Reading the slides I find:
Assuming than (x_i, y_i) represents the coordinates of the i.th block, ...
In consequence I assume, that "x,y" means the coordinates of the blocks.
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