Maybe some more info to make this task easier

The code of this filter is defined like this :

```
#@gui Equalize local histograms : fx_equalize_local_histograms, fx_equalize_local_histograms_preview(0)
#@gui : Strength (%) = float(75,0,100)
#@gui : Mode = choice(2,"Raw","Hard","Soft")
#@gui : Radius = int(4,1,16)
#@gui : Sigma = float(100,0,256)
#@gui : Regularization = float(8,0,32)
#@gui : Reduce halos = bool(1)
#@gui : sep = separator(), Channel(s) = choice(16,"All","RGBA [all]","RGB [all]","RGB [red]","RGB [green]","RGB [blue]","RGBA [alpha]","Linear RGB [all]","Linear RGB [red]","Linear RGB [green]","Linear RGB [blue]","YCbCr [luminance]","YCbCr [blue-red chrominances]","YCbCr [blue chrominance]","YCbCr [red chrominance]","YCbCr [green chrominance]","Lab [lightness]","Lab [ab-chrominances]","Lab [a-chrominance]","Lab [b-chrominance]","Lch [ch-chrominances]","Lch [c-chrominance]","Lch [h-chrominance]","HSV [hue]","HSV [saturation]","HSV [value]","HSI [intensity]","HSL [lightness]","CMYK [cyan]","CMYK [magenta]","CMYK [yellow]","CMYK [key]","YIQ [luma]","YIQ [chromas]")
#@gui : sep = separator(), Preview type = choice("Full","Forward horizontal","Forward vertical","Backward horizontal","Backward vertical","Duplicate top","Duplicate left","Duplicate bottom","Duplicate right")
#@gui : sep = separator(), note = note("<small>Author: <i>David Tschumperlé</i>. Latest update: <i>2018/01/31</i>.</small>")
fx_equalize_local_histograms :
b0="normal" b1="overlay" b2="softlight"
repeat $! l[$>]
+ac "_fx_equalize_local_histograms ${1-6}",$7,1
blend ${b$2},{$1%}
endl done
_fx_equalize_local_histograms :
+n 0,511 round.
f. "
init(
const boundary = 1;
const N = $3;
const sigma = ($6?1:-1)*(0.1+$4);
weights = vector512();
for (k = 0, k<size(weights), ++k, # Pre-compute exponentials
weights[k] = sigma>=0?exp(-sqr(k/sigma)):1 - exp(-sqr(k/sigma))
);
);
bins = vector512(0);
for (c = 0, c<s, ++c,
V = crop(x - N,y - N,0,c,2*N+1,2*N+1,1,1);
for (k = 0, k<size(V), ++k, # Compute local weighted histogram
val = V[k];
diff = abs(val - V[size(V)/2]);
bins[val]+=weights[diff];
);
);
sum = 0;
for (k = 0, k<size(bins), ++k,
sum+=bins[k];
bins[k] = sum;
);
bins/=max(1e-5,sum);
P = I;
size(P)==1?(P = bins[P[0]]; 0):
size(P)==2?(P = [ bins[P[0]], bins[P[1]] ]; 0):
size(P)==3?(P = [ bins[P[0]], bins[P[1]], bins[P[2]] ]; 0):
size(P)==4?(P = [ bins[P[0]], bins[P[1]], bins[P[2]], bins[P[3]] ]; 0);
P"
n. 0,255
if $5 norm.. bilateral. ..,$5,{2+$5} fi
k.
fx_equalize_local_histograms_preview :
gui_split_preview "fx_equalize_local_histograms $*",$-1
```

Basically, what it does is :

- For each pixel of the image, it computes the histogram of a neighborhood of size
`(2*N+1)x(2*N+1)`

where `N`

is the radius parameter. Then it computes the cumulative histogram, and use this as a function to equalize the histogram locally.
- Instead of computing the classical histogram, it computes a weighted version of the histogram, in order to favor or exclude pixel values in the neighborhood that have a similar value as the center pixel. This part probably needs a bit of reworking anyway