feat(image): resize images and crop horizon at runtime

vendor/github.com/disintegration/imaging/histogram.go

@@ -0,0 +1,52 @@
+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
+}