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package imaging
import (
"image"
)
// Histogram returns a normalized histogram of an image.
//
// Resulting histogram is represented as an array of 256 floats, where
// histogram[i] is a probability of a pixel being of a particular luminance i.
func Histogram(img image.Image) [256]float64 {
src := toNRGBA(img)
width := src.Bounds().Max.X
height := src.Bounds().Max.Y
var histogram [256]float64
var total float64
if width == 0 || height == 0 {
return histogram
}
for y := 0; y < height; y++ {
for x := 0; x < width; x++ {
i := y*src.Stride + x*4
r := src.Pix[i+0]
g := src.Pix[i+1]
b := src.Pix[i+2]
var y float32 = 0.299*float32(r) + 0.587*float32(g) + 0.114*float32(b)
histogram[int(y+0.5)]++
total++
}
}
for i := 0; i < 256; i++ {
histogram[i] = histogram[i] / total
}
return histogram
}
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