tigerBin 发表于3个月前

• 发表于 3个月前
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1.首先构造像素的频率直方图

2. 寻找直方图中的两个最大的波峰

3. 寻找这两个波峰之间的最小的波谷

4.波谷的index（像素值）为 K 值（阈值）

``````
#include "JpegDecoder.h"
#include <stdio.h>
#include <opencv2/highgui.hpp>
#include <math.h>

using namespace JpegCodec;

static cv::Mat ConvertToMat(Matrix &mat)
{
int channel = CV_8UC3;
if (mat.channal == 1) channel = CV_8UC1;

cv::Mat img(mat.rows, mat.cols, channel);  // create a new matrix

for (int i = 0; i < mat.rows * mat.cols * mat.channal; i++)
{
img.data[i] = mat.data[i];
}

return img;
}

typedef struct
{
int index;
int freq; // frequence
}Point;

void Binary(Matrix &mat)
{
Point peaks[256]; // 波峰
int histogram[256];     //直方图

// 构造直方图
for (int i = 0; i < 255; i++) histogram[i] = 0;
int cnt = mat.rows * mat.cols * mat.channal;
for (int i = 0; i < cnt; i++)
{
histogram[mat.data[i]] ++;
}

// 统计波峰
int size = 0;
for (int i = 1; i < 254; i++)
{
if (histogram[i] > histogram[i + 1] && histogram[i] < histogram[i - 1])
{
peaks[size].index = i;
peaks[size].freq = histogram[i];
size++;
}
}

// 寻找最大的两个波峰
Point max = peaks[0], snd = peaks[0];
for (int i = 0; i < size; i++)
{
if (peaks[i].freq > max.freq)
{
snd = max;
max = peaks[i];
}
else if (peaks[i].freq > snd.freq)
{
snd = peaks[i];
}
}

// 寻找波谷
int i = (max.index > snd.index ? snd.index : max.index);
size = (max.index > snd.index ? max.index : snd.index);
Point K = max;
for (; i < size; i++)
{
if (histogram[i] < K.freq)
{
K.freq = histogram[i];
K.index = i;
}
}

//二值化
for (i = 0; i < cnt; i++)
{
if (mat.data[i] < K.index) mat.data[i] = 0;
else mat.data[i] = 255;
}
}

void ShowImage(Matrix &mat)
{
cv::Mat img = ConvertToMat(mat);
cv::imshow("Bitmap", img);
}

void Gray(Matrix &dst, Matrix &src)
{
dst.Create(src.rows, src.cols, 1);

for (int i = 0; i < src.rows; i++)
{
for (int j = 0; j < src.cols; j++)
{
int idx = (i * src.rows + j) * 3;
dst.data[idx / 3] = (src.data[idx] + src.data[idx + 1] + src.data[idx + 2]) / 3;
}
}
}

int main(int argc, char *arrv[])
{
JpegDecoder decoder("01.jpg");
Matrix mat, dst;
decoder.Decoder(mat);

Gray(dst, mat);
Binary(dst);
ShowImage(dst);

cvWaitKey(0);
return 0;
}``````

JpegCodec : https://github.com/lzb-cc/JpegCodecs

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