Colorhist
Histgrapm of colors
val store_sample : int array -> Color.rgb -> unit
val gamma : float -> < height : int; unsafe_get : int -> int -> Color.rgb; width : int; .. > -> OImages.rgb24
val filter : ('a -> int array -> Color.rgb -> Color.rgb) -> 'a -> < height : int; unsafe_get : int -> int -> Color.rgb; width : int; .. > -> OImages.rgb24