1package imaging
2
3import (
4 "image"
5 "math"
6 "runtime"
7 "sync"
8)
9
10// parallel processes the data in separate goroutines.
11func parallel(start, stop int, fn func(<-chan int)) {
12 count := stop - start
13 if count < 1 {
14 return
15 }
16
17 procs := runtime.GOMAXPROCS(0)
18 if procs > count {
19 procs = count
20 }
21
22 c := make(chan int, count)
23 for i := start; i < stop; i++ {
24 c <- i
25 }
26 close(c)
27
28 var wg sync.WaitGroup
29 for i := 0; i < procs; i++ {
30 wg.Add(1)
31 go func() {
32 defer wg.Done()
33 fn(c)
34 }()
35 }
36 wg.Wait()
37}
38
39// absint returns the absolute value of i.
40func absint(i int) int {
41 if i < 0 {
42 return -i
43 }
44 return i
45}
46
47// clamp rounds and clamps float64 value to fit into uint8.
48func clamp(x float64) uint8 {
49 v := int64(x + 0.5)
50 if v > 255 {
51 return 255
52 }
53 if v > 0 {
54 return uint8(v)
55 }
56 return 0
57}
58
59func reverse(pix []uint8) {
60 if len(pix) <= 4 {
61 return
62 }
63 i := 0
64 j := len(pix) - 4
65 for i < j {
66 pi := pix[i : i+4 : i+4]
67 pj := pix[j : j+4 : j+4]
68 pi[0], pj[0] = pj[0], pi[0]
69 pi[1], pj[1] = pj[1], pi[1]
70 pi[2], pj[2] = pj[2], pi[2]
71 pi[3], pj[3] = pj[3], pi[3]
72 i += 4
73 j -= 4
74 }
75}
76
77func toNRGBA(img image.Image) *image.NRGBA {
78 if img, ok := img.(*image.NRGBA); ok {
79 return &image.NRGBA{
80 Pix: img.Pix,
81 Stride: img.Stride,
82 Rect: img.Rect.Sub(img.Rect.Min),
83 }
84 }
85 return Clone(img)
86}
87
88// rgbToHSL converts a color from RGB to HSL.
89func rgbToHSL(r, g, b uint8) (float64, float64, float64) {
90 rr := float64(r) / 255
91 gg := float64(g) / 255
92 bb := float64(b) / 255
93
94 max := math.Max(rr, math.Max(gg, bb))
95 min := math.Min(rr, math.Min(gg, bb))
96
97 l := (max + min) / 2
98
99 if max == min {
100 return 0, 0, l
101 }
102
103 var h, s float64
104 d := max - min
105 if l > 0.5 {
106 s = d / (2 - max - min)
107 } else {
108 s = d / (max + min)
109 }
110
111 switch max {
112 case rr:
113 h = (gg - bb) / d
114 if g < b {
115 h += 6
116 }
117 case gg:
118 h = (bb-rr)/d + 2
119 case bb:
120 h = (rr-gg)/d + 4
121 }
122 h /= 6
123
124 return h, s, l
125}
126
127// hslToRGB converts a color from HSL to RGB.
128func hslToRGB(h, s, l float64) (uint8, uint8, uint8) {
129 var r, g, b float64
130 if s == 0 {
131 v := clamp(l * 255)
132 return v, v, v
133 }
134
135 var q float64
136 if l < 0.5 {
137 q = l * (1 + s)
138 } else {
139 q = l + s - l*s
140 }
141 p := 2*l - q
142
143 r = hueToRGB(p, q, h+1/3.0)
144 g = hueToRGB(p, q, h)
145 b = hueToRGB(p, q, h-1/3.0)
146
147 return clamp(r * 255), clamp(g * 255), clamp(b * 255)
148}
149
150func hueToRGB(p, q, t float64) float64 {
151 if t < 0 {
152 t++
153 }
154 if t > 1 {
155 t--
156 }
157 if t < 1/6.0 {
158 return p + (q-p)*6*t
159 }
160 if t < 1/2.0 {
161 return q
162 }
163 if t < 2/3.0 {
164 return p + (q-p)*(2/3.0-t)*6
165 }
166 return p
167}