I am reading and trying to implement a research paper. It uses openGL to define which part of an image to use in order to reconstitute a big image composited of several images.
In order to do so, I have to generate several masks and multiply them together for each image.
One mask is the "focus mask", and they say:
We evaluate the per-pixel "focusness" of the source image using a sharpness operator that is the energy of the image Laplacian applied on a window of 20x20 pixels centered on each evaluated points.
My incomprehension is that: isn't Laplacian filter the convolution matrix:
0 -1 0 or -1 -1 -1 -1 4 -1 -1 8 -1 0 -1 0 -1 -1 -1
But it's of size 3 x 3 and not 20 x 20. The fact that I'm not a native english speaker maybe fools me on the words and there is something I don't understand in this sentence...
EDIT : The PDF with the article is downloadable here for free. => §4.1 : Focus Mask