我一直在学习计算机视觉，并想在 C 中实现一些简单的技术。对于第一个技术，我正在做 Sobel 边缘检测滤波器。我理解它是如何工作的，所以我认为它应该很容易编码，但我得到了非常奇怪的结果。
我正在使用以下图片：
结果得到了这个
新结果！：
应该注意的是，我使用的是 .ppm 图像格式（链接是 jpgs，因为我找不到支持 .ppm 的图像主机）
无论如何，这是我实现 Sobel 的代码部分：
/**********************************************************
This program takes in an image file and applies the Sobel
Filter edge detection technique to it.
**********************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "ppmReader.h"
void sobelFilter(){
//Sobel kernels dx (horizontal) and dy (vertical)
int horizFilter[3][3] = {{ 1, 0, -1},
{ 2, 0, -2},
{ 1, 0, -1}};
int vertFilter[3][3] = {{ 1, 2, 1},
{ 0, 0, 0},
{-1, -2, -1}};
int pixVal = 0;
int horizPixVal = 0;
int vertPixVal = 0;
int x, y, i, j;
//Quick check to make sure dimensions are correct
printf("Using a Width of: %d\n", width);
printf("Using a Height of: %d\n\n", height);
//Start filtering process here
for(x = 0; x < width; x++){
for(y = 0; y < height; y++){
pixVal = 0;
horizPixVal = 0;
vertPixVal = 0;
if(!((x == 0) || (x == width-1) || (y == 0) || (y == height-1))){ //If the current pixel is along the border, ignore it and set to zero
for(i = -1; i <= 1; i++){ //because the kernel does not align to it
for(j = -1; j <= 1; j++){
horizPixVal += (int)(image[y + j][x + i][0]) * horizFilter[i + 1][j + 1]; //Only need to focus on one of the RGB values since the output is
vertPixVal += (int)(image[y + j][x + i][0]) * vertFilter[i + 1][j + 1]; //greyscale and all three values are the same
}
}
}
pixVal = sqrt((horizPixVal * horizPixVal) + (vertPixVal * vertPixVal)); //Calculate magnitude
pixVal = sqrt(horizPixVal * horizPixVal);
if(pixVal > 255) pixVal = 255; //Clamp value within 8-bit range
filteredImage[y][x][0] = (unsigned char)pixVal;
}
}
}
这是读取 .ppm 文件的代码：
unsigned char image[MAX_IMAGE_HEIGHT][MAX_IMAGE_WIDTH][3];
unsigned char filteredImage[MAX_IMAGE_HEIGHT][MAX_IMAGE_WIDTH][3];
void readPPMImageData(){
char fileName[MAX_NAME];
char imageBuff[MAX_BUFF];
width = 0;
height = 0;
maxColor = 0;
int x;
int y;
FILE* file;
printf("------------------------------------------------------------\n");
printf("Now attempting to read in the .ppm image file data...\n");
printf("------------------------------------------------------------\n\n");
printf("What is the image file name (*.ppm)? : ");
scanf("%s", fileName);
file = fopen(fileName, "rb"); //open the file specified by the user in binary read mode
if(file == NULL){ //but if the file was not found, terminate program
printf("\nThe file %s could not be found! Terminating program...\n", fileName);
exit(1);
}
//The first step is to read in the file type and check it agains P6 (file type of .ppm images)
fgets(imageBuff, MAX_BUFF, file);
if(imageBuff[0] != 'P' || imageBuff[1] != '6'){
printf("\nInvalid image type! Acceptable type is: %s --- Received type is: %c%c\n\n", "P6", imageBuff[0], imageBuff[1]);
}
printf("Magic Number is: %c%c\n", imageBuff[0], imageBuff[1]);
while(width == 0 || height == 0){
fgets(imageBuff, MAX_BUFF, file);
if(imageBuff[0] != '#') {
sscanf(imageBuff, "%d %d", &width, &height);
}
}
printf("Width is: %d\n", width);
printf("Height is: %d\n", height);
//if(feof(file)){
//
//}
while(maxColor == 0){
fgets(imageBuff, MAX_BUFF, file);
if(imageBuff[0] != '#') {
sscanf(imageBuff, "%d", &maxColor);
}
}
printf("Maximum color value is: %d\n", maxColor);
for(x = 0; x < width; x++){
for(y = 0; y < height; y++){
image[y][x][0] = (unsigned char)fgetc(file); //Get Red value
image[y][x][1] = (unsigned char)fgetc(file); //Get Green value
image[y][x][2] = (unsigned char)fgetc(file); //Get Blue value
}
}
printf("Finished reading image data!\n\n");
fclose(file);
}
这是过滤后创建新 .ppm 文件的代码：
void createPPMImage(){
char fileName[MAX_NAME];
FILE* file;
int x;
int y;
printf("------------------------------------------------------------\n");
printf("Now attempting to create new .ppm image file...\n");
printf("------------------------------------------------------------\n\n");
printf("What is the name of the output image file (*.ppm)? : ");
scanf("%s", fileName);
printf("Width is: %d\n", width);
printf("Height is: %d\n", height);
printf("Maximum color value is: %d\n", maxColor);
file = fopen(fileName, "wb");
fputs("P6\n", file);
fprintf(file, "%d %d\n", width, height);
fprintf(file, "%d\n", maxColor);
for(x = 0; x < width; x++){
for(y = 0; y < height; y++){
fputc(filteredImage[y][x][0], file); //Write Red value
fputc(filteredImage[y][x][0], file); //Write Green value
fputc(filteredImage[y][x][0], file); //Write Blue value
}
}
printf("Finished creating new filtered image!\n\n");
fclose(file);
}
我 100% 确定问题不在于图像的读取或写入，因为我在没有应用过滤器的情况下测试了这些功能，并且只有在使用上述功能后才会出现问题。
感谢您提供任何帮助，因为据我所知，索引/公式似乎已正确实现，但这显然不是真的。
编辑：正如 Dave 和其他人所指出的，我不再 100% 确定错误在 Sobel 函数内，而且这似乎只是我在使用 .ppm 格式时犯的一些索引错误。我继续发布了我的 .ppm 读取器/写入器函数的代码，以及应用下面 anatolyg 提出的 [y][x][color] 方案后得到的新结果。如果我的帖子太长，我很抱歉，如果是，请告诉我，因为这是我的第一篇帖子，我还不完全确定什么是正确的。