拾取像素值时出现问题 [英] Problem with picking up pixel value

问题描述

嘿伙计们！我是这个论坛的新手。我写了一个函数来解决从.bmp图像文件中获取像素值的问题。当我尝试读取文件的第10个字节（表示图像信息的开头）时，它没问题。但是当我尝试读取第一个像素时，我从fread（）函数得到一个-92值。你可以帮我修改我的代码吗？

  void  get_pixels（ char  path []）{
  int  i，j =  0 ; 
  int  offset; 
  char 深度; 
 FILE * fp; 
  char  bmp [ 5 ]; 
 
  for （i = strlen（path） -   4 ; i< strlen （路径）; i ++）{
 bmp [j] = path [i]; 
 j ++; 
} 
  if （strstr（bmp，  .bmp）== NULL）{
 printf（  \ nIndicare un file .bmp来了immagine！\ n）; 
退出（ 1 ）; 
} 
 
 fp = fopen（路径，  rb ）; 
 
 fseek（fp， 28 ，SEEK_SET）; 
 fscanf（fp， ％c，& depth）; 
 
  if （深度！=  8 ）{
 printf（   \ nSelezionare una immagine a 8 bit！\ n）; 
退出（ 2 ）; 
} 
 
 fseek（fp， 10 ，SEEK_SET）; 
 fread（& offset， sizeof （offset）， 1 ，fp）; 
 printf（  \ n％d，offset）; 
 
 fseek（fp，offset，SEEK_SET）; 
 fread（& pixels [ 0 ]， sizeof （ char ）， 1 ，fp）; 
 printf（  \ n％d，像素[ 0 ]）; 
 
 fclose（fp）; 
} 

对不起我的英文，我是意大利人......：D

解决方案

char 是签名类型。您应该使用 unsigned char 。

尝试

  unsigned   char  *像素; 
  //   ...分配'像素'缓冲区 
  //   ...  
 fseek（fp，offset，SEEK_SET）; 
 fread（& pixels [ 0 ]， sizeof （pixels [ 0 ]）， 1 ，fp）; 
 printf（  \ n％d，像素[ 0 ]）; 

Hey guys! I'm new in this forum. I have a problem with a function I wrote to pick up pixel values from a .bmp image file. When I try to read the 10th byte of the file(which indicates the beginning of the image's information), it's allright. But when I try to read the first pixel I get a -92 as value from the fread() function. Can you please help me to fix my code?

void get_pixels(char path[]){
int i, j=0;
int offset;
char depth;
FILE *fp;
char bmp[5];
	
	for(i=strlen(path)-4;i<strlen(path);i++){
		bmp[j]=path[i];
		j++;
	}
	if(strstr(bmp, ".bmp")==NULL){
		printf("\nIndicare un file .bmp come immagine!\n");
		exit(1);
	}
	
	fp = fopen(path, "rb");
	
	fseek(fp, 28, SEEK_SET);
	fscanf(fp, "%c", &depth);
	
	if(depth!=8){
		printf("\nSelezionare una immagine a 8 bit!\n");
		exit(2);
	}
	
	fseek(fp, 10, SEEK_SET);
	fread(&offset, sizeof(offset), 1, fp);
	printf("\n%d", offset);
	
	fseek(fp, offset, SEEK_SET);
	fread(&pixels[0], sizeof(char), 1, fp);
	printf("\n%d", pixels[0]);
	
	fclose(fp);
}

Sorry for my english, I'm italian... :D

解决方案

char is a signed type. You should use instead a unsigned char.
Try

unsigned char * pixels;
//... allocate 'pixels' buffer
//...
fseek(fp, offset, SEEK_SET);
fread(&pixels[0], sizeof(pixels[0]), 1, fp);
printf("\n%d", pixels[0]);

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