Kuwahara Filtering

This algorithm was invented with fixing images with missing pixels.
It however doesn't work that well for that, but what it works well for is art.

[Wikipedia](https://en.wikipedia.org/wiki/Kuwahara_filter)

Kuwahara Filtering works like a blur algorithm.

Here are the needed steps:
1. Imagine a rectangle around each pixel
2. Divide the rectangle into 4 equally sized sectors
3. For each sector get the average color and the color deviation
4. Lastly pick the sector with the smallest deviation and use its color

I've somehow implemented the algorithm, but it is far from acceptable.
Here is the result:

Image before:

And after:

With a bigger texel size _{**(I didn't implement the texel size computation)**}:

Inizia dall’articolo di Wikipedia collegato per comprendere il filtro Kuwahara, quindi individua l’implementazione esistente a cui fa riferimento l’issue. Confronta il suo output con il processo descritto a quattro settori e determina come debba essere calcolata la dimensione del texel. Il lavoro è completo quando il filtro produce il risultato artistico previsto e gestisce il calcolo mancante della dimensione del texel.

Scritto dal modello di indicizzazione a partire dal testo della issue.