灰度图像时0到255之间的像素,哪个函数能把它变成0到1之间的像素

Posted 2023-05-07

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k=im2bw(r,170/255);
%其中的r是你的二维矩阵，170是自己取的，小于170，则二值化为0，大于170二值化为1 参考技术A y=(1/255)*x 参考技术B y=1/255*x ,也许是追问

b=rgb2gray(a); %转化为灰度图像
q=im2double(b);
f=im2double(b); %将无符号的8位图像转换为双精度类型
这样就行了吧

追答

应该是

音视频 - YUV像素处理

将一帧YUV图像变成黑白照，只保留Y数据（灰度图）

我们把UV数据去掉，只写入Y数据，那么只剩下Y数据，打开图片的时候选择一定要选择以“Y”格式打开，而不是“YUV420”格式打开。

#include <stdio.h>
#include <stdlib.h>

#define startImage "lena_256x256_yuv420p.yuv"

int main()
{
        FILE *fp  = NULL;
        FILE *fp1 = NULL;

        unsigned char *readBuf;
        readBuf = (unsigned char *)malloc(256*256*3/2);

        fp  = fopen(startImage,"rb+");
        fp1 = fopen("new_256x256_yuv420p.y","wb+");

        fread(readBuf,1,256*256,fp);

        fwrite(readBuf,1,256*256,fp1);

        free(readBuf);
        fclose(fp);
        fclose(fp1);
        return 0;
}

用yuv420格式打开的样子

用y格式打开的样子

将一帧YUV图像变成黑白照，将UV置0（灰度图）

上面只保存了Y数据，准确来说不算是YUV图像，我们不把UV拿掉，将U和V的数据修改为0就代表无色，让他置0也可以让他呈现黑白照。

U、V是图像中的经过偏置处理的色度分量。在偏置处理前，它的取值范围是-128-127，这时，把U和V数据修改为0代表无色。在偏置处理后，它的取值范围变成了0-255，所以这时候需要取中间值，即128。所以我们下面要将U和V数据修改为128

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define outPutFileName "testGrey.yuv"

int testYuv420Grey(char *fileName, int width, int height)
{
    FILE *fp;
    FILE *fp1;
    unsigned char *readBuf;
    readBuf = (unsigned char *)malloc(width*height*3/2);
    fp = fopen(fileName, "rb+");
    fp1 = fopen(outPutFileName, "wb+");

    /* read yuv file */
    fread(readBuf, 1, width*height, fp);

    /* memset U and V*/
    memset(readBuf+width*height, 128, width*height/2);

    /* create new file */
    fwrite(readBuf, 1, width*height*3/2, fp1);
	
	free(readBuf);
    fclose(fp);
    fclose(fp1);
    return 0;
}

int main()
{
    testYuv420Grey("lena_256x256_yuv420p.yuv", 256, 256);
    return 0;
}

将一帧YUV图像U值置0，其他不动

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define outPutFileName "test0u.yuv"

int testYuv420Grey(char *fileName, int width, int height)
{
    FILE *fp;
    FILE *fp1;
    unsigned char *readBuf;
    readBuf = (unsigned char *)malloc(width*height*3/2);
    fp = fopen(fileName, "rb+");
    fp1 = fopen(outPutFileName, "wb+");

    /* read yuv file */
    fread(readBuf, 1, width*height, fp);

    /* memset U*/
    memset(readBuf+width*height, 128, width*height/4);

    /* create new file */
    fwrite(readBuf, 1, width*height*3/2, fp1);
	
	free(readBuf);
    fclose(fp);
    fclose(fp1);
    return 0;
}

int main()
{
    testYuv420Grey("lena_256x256_yuv420p.yuv", 256, 256);
    return 0;
}

将一帧YUV图像V值置0，其他不动

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define outPutFileName "test0v.yuv"

int testYuv420Grey(char *fileName, int width, int height)
{
    FILE *fp;
    FILE *fp1;
    unsigned char *readBuf;
    readBuf = (unsigned char *)malloc(width*height*3/2);
    fp = fopen(fileName, "rb+");
    fp1 = fopen(outPutFileName, "wb+");

    /* read yuv file */
    fread(readBuf, 1, width*height, fp);

    /* memset V */
    memset(readBuf+width*height*5/4, 128, width*height/4);

    /* create new file */
    fwrite(readBuf, 1, width*height*3/2, fp1);
	
	free(readBuf);
    fclose(fp);
    fclose(fp1);
    return 0;
}

int main()
{
    testYuv420Grey("lena_256x256_yuv420p.yuv", 256, 256);
    return 0;
}

将Y(亮度)值减半

#include <stdio.h>
#include <stdlib.h>

#define startImage "lena_256x256_yuv420p.yuv"

int main()
{
        FILE *fp  = NULL;
        FILE *fp1 = NULL;
        int  nIdx = 0;

        unsigned char *readBuf;
        readBuf = (unsigned char *)malloc(256*256*3/2);

        fp  = fopen(startImage,"rb+");
        fp1 = fopen("halfbrightness.yuv","wb+");

        fread(readBuf,1,256*256*3/2,fp);

        for(nIdx=0;nIdx<256*256;nIdx++)
        {
                readBuf[nIdx] = readBuf[nIdx]/2;
        }

        fwrite(readBuf,1,256*256*3/2,fp1);

        free(readBuf);
        fclose(fp);
        fclose(fp1);
        return 0;
}