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
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
use std::cmp::{min, max};
use image::{GrayImage, ImageBuffer, Luma};
use definitions::{HasBlack, HasWhite};
use integral_image::{integral_image, sum_image_pixels};
use stats::{cumulative_histogram, histogram};
use rayon::prelude::*;
pub fn adaptive_threshold(image: &GrayImage, block_radius: u32) -> GrayImage {
assert!(block_radius > 0);
let integral = integral_image(image);
let mut out = ImageBuffer::from_pixel(image.width(), image.height(), Luma::black());
for y in 0..image.height() {
for x in 0..image.width() {
let current_pixel = image.get_pixel(x, y);
let (y_low, y_high) = (
max(0, y as i32 - (block_radius as i32)) as u32,
min(image.height() - 1, y + block_radius),
);
let (x_low, x_high) = (
max(0, x as i32 - (block_radius as i32)) as u32,
min(image.width() - 1, x + block_radius),
);
let w = (y_high - y_low + 1) * (x_high - x_low + 1);
let mean = sum_image_pixels(&integral, x_low, y_low, x_high, y_high) / w;
if current_pixel[0] as u32 >= mean as u32 {
out.put_pixel(x, y, Luma::white());
}
}
}
out
}
pub fn otsu_level(image: &GrayImage) -> u8 {
let hist = histogram(image);
let (width, height) = image.dimensions();
let total_weight = width * height;
let total_pixel_sum = hist.iter().enumerate().fold(0f64, |sum, (t, h)| {
sum + (t as u32 * h) as f64
});
let mut background_pixel_sum = 0f64;
let mut background_weight = 0u32;
let mut foreground_weight;
let mut largest_variance = 0f64;
let mut best_threshold = 0u8;
for (threshold, hist_count) in hist.iter().enumerate() {
background_weight = background_weight + hist_count;
if background_weight == 0 {
continue;
};
foreground_weight = total_weight - background_weight;
if foreground_weight == 0 {
break;
};
background_pixel_sum += (threshold as u32 * hist_count) as f64;
let foreground_pixel_sum = total_pixel_sum - background_pixel_sum;
let background_mean = background_pixel_sum / (background_weight as f64);
let foreground_mean = foreground_pixel_sum / (foreground_weight as f64);
let mean_diff_squared = (background_mean - foreground_mean).powi(2);
let intra_class_variance = (background_weight as f64) * (foreground_weight as f64) *
mean_diff_squared;
if intra_class_variance > largest_variance {
largest_variance = intra_class_variance;
best_threshold = threshold as u8;
}
}
best_threshold
}
pub fn threshold(image: &GrayImage, thresh: u8) -> GrayImage {
let mut out = image.clone();
threshold_mut(&mut out, thresh);
out
}
pub fn threshold_mut(image: &mut GrayImage, thresh: u8) {
for p in image.iter_mut() {
*p = if *p <= thresh { 0 } else { 255 };
}
}
pub fn equalize_histogram_mut(image: &mut GrayImage) {
let hist = cumulative_histogram(image);
let total = hist[255] as f32;
image.par_iter_mut().for_each(|p| {
let fraction = unsafe { *hist.get_unchecked(*p as usize) as f32 / total };
*p = (f32::min(255f32, 255f32 * fraction)) as u8;
});
}
pub fn equalize_histogram(image: &GrayImage) -> GrayImage {
let mut out = image.clone();
equalize_histogram_mut(&mut out);
out
}
pub fn match_histogram_mut(image: &mut GrayImage, target: &GrayImage) {
let image_histc = cumulative_histogram(image);
let target_histc = cumulative_histogram(target);
let lut = histogram_lut(&image_histc, &target_histc);
for p in image.iter_mut() {
*p = lut[*p as usize] as u8;
}
}
pub fn match_histogram(image: &GrayImage, target: &GrayImage) -> GrayImage {
let mut out = image.clone();
match_histogram_mut(&mut out, target);
out
}
fn histogram_lut(source_histc: &[u32; 256], target_histc: &[u32; 256]) -> [usize; 256] {
let source_total = source_histc[255] as f32;
let target_total = target_histc[255] as f32;
let mut lut = [0usize; 256];
let mut y = 0usize;
let mut prev_target_fraction = 0f32;
for s in 0..256 {
let source_fraction = source_histc[s] as f32 / source_total;
let mut target_fraction = target_histc[y] as f32 / target_total;
while source_fraction > target_fraction && y < 255 {
y += 1;
prev_target_fraction = target_fraction;
target_fraction = target_histc[y] as f32 / target_total;
}
if y == 0 {
lut[s] = y;
} else {
let prev_dist = f32::abs(prev_target_fraction - source_fraction);
let dist = f32::abs(target_fraction - source_fraction);
if prev_dist < dist {
lut[s] = y - 1;
} else {
lut[s] = y;
}
}
}
lut
}
pub fn stretch_contrast(image: &GrayImage, lower: u8, upper: u8) -> GrayImage {
let mut out = image.clone();
stretch_contrast_mut(&mut out, lower, upper);
out
}
pub fn stretch_contrast_mut(image: &mut GrayImage, lower: u8, upper: u8) {
assert!(upper > lower, "upper must be strictly greater than lower");
let len = (upper - lower) as u16;
for p in image.iter_mut() {
if *p >= upper {
*p = 255;
} else if *p <= lower {
*p = 0;
} else {
let scaled = (255 * (*p as u16 - lower as u16)) / len;
*p = scaled as u8;
}
}
}
#[cfg(test)]
mod test {
use super::*;
use definitions::{HasBlack, HasWhite};
use utils::gray_bench_image;
use image::{GrayImage, Luma};
use test::{Bencher, black_box};
#[test]
fn adaptive_threshold_constant() {
let image = GrayImage::from_pixel(3, 3, Luma([100u8]));
let binary = adaptive_threshold(&image, 1);
let expected = GrayImage::from_pixel(3, 3, Luma::white());
assert_pixels_eq!(expected, binary);
}
#[test]
fn adaptive_threshold_one_darker_pixel() {
for y in 0..3 {
for x in 0..3 {
let mut image = GrayImage::from_pixel(3, 3, Luma([200u8]));
image.put_pixel(x, y, Luma([100u8]));
let binary = adaptive_threshold(&image, 1);
let mut expected = GrayImage::from_pixel(3, 3, Luma::white());
expected.put_pixel(x, y, Luma::black());
assert_pixels_eq!(binary, expected);
}
}
}
#[test]
fn adaptive_threshold_one_lighter_pixel() {
for y in 0..5 {
for x in 0..5 {
let mut image = GrayImage::from_pixel(5, 5, Luma([100u8]));
image.put_pixel(x, y, Luma([200u8]));
let binary = adaptive_threshold(&image, 1);
for yb in 0..5 {
for xb in 0..5 {
let output_intensity = binary.get_pixel(xb, yb)[0];
let is_light_pixel = xb == x && yb == y;
let local_mean_includes_light_pixel = (yb as i32 - y as i32).abs() <= 1 &&
(xb as i32 - x as i32).abs() <= 1;
if is_light_pixel {
assert_eq!(output_intensity, 255);
} else if local_mean_includes_light_pixel {
assert_eq!(output_intensity, 0);
} else {
assert_eq!(output_intensity, 255);
}
}
}
}
}
}
#[bench]
fn bench_adaptive_threshold(b: &mut Bencher) {
let image = gray_bench_image(200, 200);
let block_radius = 10;
b.iter(|| {
let thresholded = adaptive_threshold(&image, block_radius);
black_box(thresholded);
});
}
#[bench]
fn bench_match_histogram(b: &mut Bencher) {
let target = GrayImage::from_pixel(200, 200, Luma([150]));
let image = gray_bench_image(200, 200);
b.iter(|| {
let matched = match_histogram(&image, &target);
black_box(matched);
});
}
#[bench]
fn bench_match_histogram_mut(b: &mut Bencher) {
let target = GrayImage::from_pixel(200, 200, Luma([150]));
let mut image = gray_bench_image(200, 200);
b.iter(|| { match_histogram_mut(&mut image, &target); });
}
#[test]
fn test_histogram_lut_source_and_target_equal() {
let mut histc = [0u32; 256];
for i in 1..histc.len() {
histc[i] = 2 * i as u32;
}
let lut = histogram_lut(&histc, &histc);
let expected = (0..256).collect::<Vec<_>>();
assert_eq!(&lut[0..256], &expected[0..256]);
}
#[test]
fn test_histogram_lut_gradient_to_step_contrast() {
let mut grad_histc = [0u32; 256];
for i in 0..grad_histc.len() {
grad_histc[i] = i as u32;
}
let mut step_histc = [0u32; 256];
for i in 30..130 {
step_histc[i] = 100;
}
for i in 130..256 {
step_histc[i] = 200;
}
let lut = histogram_lut(&grad_histc, &step_histc);
let mut expected = [0usize; 256];
expected[0] = 0;
for i in 1..64 {
expected[i] = 29;
}
for i in 64..128 {
expected[i] = 30;
}
for i in 128..192 {
expected[i] = 129;
}
for i in 192..256 {
expected[i] = 130;
}
assert_eq!(&lut[0..256], &expected[0..256]);
}
fn constant_image(width: u32, height: u32, intensity: u8) -> GrayImage {
GrayImage::from_pixel(width, height, Luma([intensity]))
}
#[test]
fn test_otsu_constant() {
assert_eq!(otsu_level(&constant_image(10, 10, 0)), 0);
assert_eq!(otsu_level(&constant_image(10, 10, 128)), 0);
assert_eq!(otsu_level(&constant_image(10, 10, 255)), 0);
}
#[test]
fn test_otsu_level_gradient() {
let contents = (0u8..26u8).map(|x| x * 10u8).collect();
let image = GrayImage::from_raw(26, 1, contents).unwrap();
let level = otsu_level(&image);
assert_eq!(level, 120);
}
#[bench]
fn bench_otsu_level(b: &mut Bencher) {
let image = gray_bench_image(200, 200);
b.iter(|| {
let level = otsu_level(&image);
black_box(level);
});
}
#[test]
fn test_threshold_0_image_0() {
let expected = 0u8;
let actual = threshold(&constant_image(10, 10, 0), 0);
assert_pixels_eq!(actual, constant_image(10, 10, expected));
}
#[test]
fn test_threshold_0_image_1() {
let expected = 255u8;
let actual = threshold(&constant_image(10, 10, 1), 0);
assert_pixels_eq!(actual, constant_image(10, 10, expected));
}
#[test]
fn test_threshold_threshold_255_image_255() {
let expected = 0u8;
let actual = threshold(&constant_image(10, 10, 255), 255);
assert_pixels_eq!(actual, constant_image(10, 10, expected));
}
#[test]
fn test_threshold() {
let original_contents = (0u8..26u8).map(|x| x * 10u8).collect();
let original = GrayImage::from_raw(26, 1, original_contents).unwrap();
let expected_contents = vec![0u8; 13].into_iter().chain(vec![255u8; 13]).collect();
let expected = GrayImage::from_raw(26, 1, expected_contents).unwrap();
let actual = threshold(&original, 125u8);
assert_pixels_eq!(expected, actual);
}
#[bench]
fn bench_equalize_histogram(b: &mut Bencher) {
let image = gray_bench_image(500, 500);
b.iter(|| {
let equalized = equalize_histogram(&image);
black_box(equalized);
});
}
#[bench]
fn bench_equalize_histogram_mut(b: &mut Bencher) {
let mut image = gray_bench_image(500, 500);
b.iter(|| { black_box(equalize_histogram_mut(&mut image)); });
}
#[bench]
fn bench_threshold(b: &mut Bencher) {
let image = gray_bench_image(500, 500);
b.iter(|| {
let thresholded = threshold(&image, 125);
black_box(thresholded);
});
}
#[bench]
fn bench_threshold_mut(b: &mut Bencher) {
let mut image = gray_bench_image(500, 500);
b.iter(|| { black_box(threshold_mut(&mut image, 125)); });
}
#[bench]
fn bench_stretch_contrast(b: &mut Bencher) {
let image = gray_bench_image(500, 500);
b.iter(|| {
let stretched = stretch_contrast(&image, 20, 80);
black_box(stretched);
});
}
#[bench]
fn bench_stretch_contrast_mut(b: &mut Bencher) {
let mut image = gray_bench_image(500, 500);
b.iter(|| { black_box(stretch_contrast_mut(&mut image, 20, 80)); });
}
}