1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
|
// Copyright 2019 Nick White.
// Use of this source code is governed by the GPLv3
// license that can be found in the LICENSE file.
package preproc
import (
"image"
"image/color"
"rescribe.xyz/integralimg"
)
// Implements Sauvola's algorithm for text binarization, see paper
// "Adaptive document image binarization" (2000)
func Sauvola(img *image.Gray, ksize float64, windowsize int) *image.Gray {
b := img.Bounds()
new := image.NewGray(b)
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
window := surrounding(img, x, y, windowsize)
m, dev := meanstddev(window)
threshold := m * (1 + ksize*((dev/128)-1))
if img.GrayAt(x, y).Y < uint8(threshold) {
new.SetGray(x, y, color.Gray{0})
} else {
new.SetGray(x, y, color.Gray{255})
}
}
}
return new
}
// Implements Sauvola's algorithm using Integral Images, see paper
// "Efficient Implementation of Local Adaptive Thresholding Techniques Using Integral Images"
// and
// https://stackoverflow.com/questions/13110733/computing-image-integral
func IntegralSauvola(img *image.Gray, ksize float64, windowsize int) *image.Gray {
b := img.Bounds()
new := image.NewGray(b)
integrals := integralimg.ToAllIntegralImg(img)
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
m, dev := integrals.MeanStdDevWindow(x, y, windowsize)
threshold := m * (1 + ksize*((dev/128)-1))
if img.GrayAt(x, y).Y < uint8(threshold) {
new.SetGray(x, y, color.Gray{0})
} else {
new.SetGray(x, y, color.Gray{255})
}
}
}
return new
}
// PreCalcedSauvola Implements Sauvola's algorithm using precalculated Integral Images
// TODO: have this be the root function that the other two reference
func PreCalcedSauvola(integrals integralimg.WithSq, img *image.Gray, ksize float64, windowsize int) *image.Gray {
b := img.Bounds()
new := image.NewGray(b)
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
m, dev := integrals.MeanStdDevWindow(x, y, windowsize)
threshold := m * (1 + ksize*((dev/128)-1))
if img.GrayAt(x, y).Y < uint8(threshold) {
new.SetGray(x, y, color.Gray{0})
} else {
new.SetGray(x, y, color.Gray{255})
}
}
}
return new
}
|
