# What kind of blur filter is this?

I have the original image and filtered image.

Original:

Filtered:

Difference:

These images are from pixiv WHICH IS NOT AT ALL SAFE FOR WORK: http://www.pixiv.net/member_illust.php?mode=manga&illust_id=43697578

It look like a linear FIR filter which mean blurred image = original image perform convolution with some window function

In theory from this 2 images I can find the window function but I don't know how to do that in practice. Do I need some tools or software to analyze?

The main question is what kind of blur filter is this? (Or if it doesn't has particular name I'm asking about window function. a name, a plot, anything)

And if you can tell by using some method or tools (not just your experience or instinct) could you tell me how?

• This is a interesting question but since your looking for a convolve filter, it might be better to ask at a more technical subsite. Anyway i think i know how to do this but i need a computer with more than text only interfacing to test this. Anyway look for matlab/mathematica axis – joojaa Aug 11 '14 at 19:08
• @joojaa Thank you for the suggestion. I have the feeling that I hardly get technical answer from here but some one may know how it done without knowing technical details. That also usable to me too. The feeling matters more than knowing the exact function. – Curious Sam Aug 11 '14 at 19:21
• It might not be a convolution matrix at all, or then it has negative lobes, must investigate further – joojaa Aug 12 '14 at 16:52
• @joojaa I guess it must have negative lobes or it will look like Gaussian blur. It's not IIR filter for sure. If it is a linear operation I'm pretty sure the result is from convolution. However, the 2 images here may not suffice to find the window function. For example the image may got resampled after blurring so the data from more than 1 pixel diffused in a pixel also if they use round up/down in the algorithm (which likely) the images will got some non-linear part mixed in. My best bet is to find someone who use this technique (I guess) but I only see this in Anime related pictures. – Curious Sam Aug 13 '14 at 8:51
• Whatabout some adaptive blur like surface blur? – joojaa Aug 13 '14 at 8:53