C 大津阈值法
我试图用大津的方法计算一个阈值。示例图像为8位灰度bmp文件 该图像的直方图由以下步骤生成:C 大津阈值法,c,image-processing,C,Image Processing,我试图用大津的方法计算一个阈值。示例图像为8位灰度bmp文件 该图像的直方图由以下步骤生成: /* INITIALIZE ARRAYS */ for(int i = 0; i < 255; i++) occurrence[i] = 0; for(int i = 0; i < 255; i++) histogram[i] = 0; /* START AT BEGINNING OF RASTER DATA */ fseek(input_img, (54 + 4 * color_numb
/* INITIALIZE ARRAYS */
for(int i = 0; i < 255; i++) occurrence[i] = 0;
for(int i = 0; i < 255; i++) histogram[i] = 0;
/* START AT BEGINNING OF RASTER DATA */
fseek(input_img, (54 + 4 * color_number), SEEK_SET);
/* READ RASTER DATA */
for(int r = 0; r <= original_img.rows - 1; r++) {
for(int c = 0; c <= original_img.cols -1; c++) {
fread(p_char, sizeof(char), 1, input_img);
pixel_value = *p_char;
/* COUNT OCCURRENCES OF PIXEL VALUE */
occurrence[pixel_value] = occurrence[pixel_value] + 1;
total_pixels++;
}
}
for(int i = 0; i <= 255; i++) {
/* TAKES NUMBER OF OCCURRENCES OF A PARTICULAR PIXEL
* AND DIVIDES BY THE TOTAL NUMBER OF PIXELS YIELDING
* A RATIO */
histogram[i] = (float) occurrence[i] / (float) total_pixels;
}
函数otsu\u方法
:
int otsu_method(float *histogram, long int total_pixels) {
double omega[256], myu[256];
double max_sigma, sigma[256];
int threshold;
omega[0] = histogram[0];
myu[0] = 0.0;
for(int i = 1; i < 256; i++) {
omega[i] = omega[i - 1] + histogram[i];
myu[i] = myu[i - 1] + i * histogram[i];
}
threshold = 0;
max_sigma = 0.0;
for(int i = 0; i < 255; i++) {
if(omega[i] != 0.0 && omega[i] != 1.0)
sigma[i] = pow(myu[255] * omega[i], 2) / (omega[i] * (1.0 - omega[i]));
else
sigma[i] = 0.0;
if(sigma[i] > max_sigma) {
max_sigma = sigma[i];
threshold = i;
}
}
printf("Threshold value: %d\n", threshold);
return threshold;
}
我认为244不是一个正确计算的阈值,因为当函数threshold_image对图像进行二值化时,所有像素都转换为黑色
如果我跳过了大津法,并从用户输入函数中获取阈值,图像就会正常工作
函数otsu_方法
是复制粘贴的代码,因此我对变量或条件不是非常清楚。
我正在学习图像处理,并试图找出一些基础知识。关于Otsu算法的任何信息以及关于我的代码的任何反馈都有帮助。我找到了导致问题的原因,并更改了函数Otsu\u方法:
int otsu_method(float *histogram, long int total_pixels) {
double probability[256], mean[256];
double max_between, between[256];
int threshold;
/*
probability = class probability
mean = class mean
between = between class variance
*/
for(int i = 0; i < 256; i++) {
probability[i] = 0.0;
mean[i] = 0.0;
between[i] = 0.0;
}
probability[0] = histogram[0];
for(int i = 1; i < 256; i++) {
probability[i] = probability[i - 1] + histogram[i];
mean[i] = mean[i - 1] + i * histogram[i];
}
threshold = 0;
max_between = 0.0;
for(int i = 0; i < 255; i++) {
if(probability[i] != 0.0 && probability[i] != 1.0)
between[i] = pow(mean[255] * probability[i] - mean[i], 2) / (probability[i] * (1.0 - probability[i]));
else
between[i] = 0.0;
if(between[i] > max_between) {
max_between = between[i];
threshold = i;
}
}
return threshold;
}
程序输出:
Reading file 512gr.bmp
Width: 512
Height: 512
File size: 263222
# Colors: 256
Vector size: 262144
Total number of pixels: 262144
Threshold value: 244
Reading file 512gr.bmp
Width: 512
Height: 512
File size: 263222
# Colors: 256
Vector size: 262144
Total number of pixels: 262144
Threshold value: 117
Probability: 0.416683
Mean: 31.9631
Between varaince: 1601.01
int otsu_method(float *histogram, long int total_pixels) {
double probability[256], mean[256];
double max_between, between[256];
int threshold;
/*
probability = class probability
mean = class mean
between = between class variance
*/
for(int i = 0; i < 256; i++) {
probability[i] = 0.0;
mean[i] = 0.0;
between[i] = 0.0;
}
probability[0] = histogram[0];
for(int i = 1; i < 256; i++) {
probability[i] = probability[i - 1] + histogram[i];
mean[i] = mean[i - 1] + i * histogram[i];
}
threshold = 0;
max_between = 0.0;
for(int i = 0; i < 255; i++) {
if(probability[i] != 0.0 && probability[i] != 1.0)
between[i] = pow(mean[255] * probability[i] - mean[i], 2) / (probability[i] * (1.0 - probability[i]));
else
between[i] = 0.0;
if(between[i] > max_between) {
max_between = between[i];
threshold = i;
}
}
return threshold;
}
between[i] = pow(mean[255] * probability[i] - mean[i], 2) / (probability[i] * (1.0 - probability[i]));
Reading file 512gr.bmp
Width: 512
Height: 512
File size: 263222
# Colors: 256
Vector size: 262144
Total number of pixels: 262144
Threshold value: 117
Probability: 0.416683
Mean: 31.9631
Between varaince: 1601.01