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let kernel (sigma : float) : float array =
let sigma = Float.max 0.1 sigma in
let half = int_of_float (Float.ceil (3. *. sigma)) in
let w = Array.init ((2 * half) + 1) (fun i -> let d = float_of_int (i - half) in exp (-.(d *. d) /. (2. *. sigma *. sigma))) in
let total = Array.fold_left ( +. ) 0. w in
Array.map (fun v -> v /. total) w
let blur ~(radius : float) (img : Pixels.image) : Pixels.image = if radius <= 0. then Pixels.copy img else Convolve.separable (kernel radius) img
let unsharp ~(amount : float) ~(radius : float) ~(threshold : int) (img : Pixels.image) : Pixels.image =
let blurred = blur ~radius img in
let out = Pixels.copy img in
for y = 0 to img.height - 1 do
for x = 0 to img.width - 1 do
for c = 0 to 2 do
let v = Pixels.get img x y c in
let detail = v - Pixels.get blurred x y c in
if abs detail >= threshold then Pixels.set out x y c (Pixels.clamp (v + int_of_float (Float.round (float_of_int detail *. amount /. 100.))))
done
done
done;
out