<p>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.</p>

<p>In order to do so, I have to generate several masks and multiply them together for each image.</p>

<p>One mask is the "focus mask", and they say:</p>

<blockquote>
  <p>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.</p>
</blockquote>

<p>My incomprehension is that: isn't Laplacian filter the convolution matrix:</p>

<pre><code> 0  -1   0   or    -1  -1  -1
-1   4  -1         -1   8  -1
 0  -1   0         -1  -1  -1
</code></pre>

<p>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...</p>

<p>EDIT : 
The PDF with the article is downloadable <a href="https://www.researchgate.net/publication/220252497_Masked_photo_blending_Mapping_dense_photographic_data_set_on_high-resolution_sampled_3D_models" rel="nofollow noreferrer">here</a> for free.
=> §4.1 : Focus Mask</p>

CC BY-SA 3.0
2017-06-09T09:53:16.497Z
That would make sense, maybe this is it. I can't tell. But that's a good idea and I will try to implement it to see.

You're right for the link, I will add it in the post.
Raph Schim
<opengl><c++><pixel-graphics><filtering>
Image Laplacian incomprehension
Raph Schim
# Image Laplacian incomprehension

(Asked by: username_0 on 2017-06-08)

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

**Tags:** opengl, c++, pixel-graphics, filtering
> **Comments:**
> **username_0**: That would make sense, maybe this is it. I can't tell. But that's a good idea and I will try to implement it to see.  You're right for the link, I will add it in the post.  

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## 0 answers

