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|
package imaging
import (
"image"
"sync"
)
// 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 {
var mu sync.Mutex
var histogram [256]float64
var total float64
src := newScanner(img)
if src.w == 0 || src.h == 0 {
return histogram
}
parallel(0, src.h, func(ys <-chan int) {
var tmpHistogram [256]float64
var tmpTotal float64
scanLine := make([]uint8, src.w*4)
for y := range ys {
src.scan(0, y, src.w, y+1, scanLine)
i := 0
for x := 0; x < src.w; x++ {
s := scanLine[i : i+3 : i+3]
r := s[0]
g := s[1]
b := s[2]
y := 0.299*float32(r) + 0.587*float32(g) + 0.114*float32(b)
tmpHistogram[int(y+0.5)]++
tmpTotal++
i += 4
}
}
mu.Lock()
for i := 0; i < 256; i++ {
histogram[i] += tmpHistogram[i]
}
total += tmpTotal
mu.Unlock()
})
for i := 0; i < 256; i++ {
histogram[i] = histogram[i] / total
}
return histogram
}
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