位图点处理

Question

会喜欢我的任务之一集思广益一些帮助。我将编写一个程序来处理.bmp图像的基本点处理。程序将打开.bmp文件进行读取和写入，并不会改变头部的任何部位，但根据命令行参数文件中的像素值：

-fromrow x, where x specifies the bottommost row to process 
-torowx, where x specifies the topmost row to process 
-fromcol x, where x specifies the leftmost column to process 
-tocol x, where x specifies the rightmost column to process 
-op x, where x is one of the following: 
    - 1 = threshold the image (any pixel value in the specifies range over 127 is changed to 255, and pixel values 127 or less is changed to 0) 
    - 2 = negative (any pixel value p in the specified range is changed to 255-p) 

To process image data, you will need to make use of the following: 
- each pixel value is an unsigned char 
- the number of rows in the image is stored as an int at position (byte address) 22 in the file 
- the number of columns in the image is stored as an int at position (byte address) 18 in the file 
- the position at which the pixel data starts is an int stored at position (byte address) 10 in the file 
- pixel information is stored row by row, starting from the bottommost row in the image (row 0) and progressing upwards. within a row; pixel information is stored left to right. padding is added to the end of each row to make row length a multiple of 4 bytes (if the row has 479 columns, there is one extra padding at the end of the row before the next row starts) 

我有点失落至于如何开始，但我想我应该做一个结构位图首先像这样？

struct bitmap { 
    unsigned int startrow; 
    unsigned int endrow; 
    unsigned int startcol; 
    unsigned int endcol; 
} 

任何人都可以帮助我通过什么，我需要做的字节地址，该任务引用？任何其他头脑风暴的建议也将不胜感激。谢谢！

Answer 1

可以通过在二进制模式打开文件读取的原始字节：

FILE *fid = fopen("blah.bmp", "rb"); 

然后可以读出的数据的一定量的这样的：

int num_actually_read = fread(p, sizeof(*p), num_to_read, fid); 

其中p是一个指向一些缓冲。在这种情况下，你可能想p是uint8_t *类型的，因为你所面对的大多是原始字节。

或者，你可以在这样一个文件跳来跳去：

fseek(fid, pos, SEEK_SET); 

我希望这是足以让你去。

Answer 2

您需要一个指针指向文件的字节地址22和18。一旦指向这些地址，您将需要取消引用指针以获取行和列值。然后你必须将你的指针指向地址10，然后逐个遍历像素。