位图点处理

Question

希望能为我的一项任务提供头脑风暴帮助。我要编写一个对 .bmp 图像进行基本点处理的程序。程序会打开一个.bmp文件进行读写，不会改变文件头的任何部分，而是根据命令行参数改变文件中的像素值：

-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)

我对如何开始有点迷茫，但我想我应该先像这样制作一个结构位图？

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

谁能帮助我了解我需要为分配引用的字节地址做些什么？任何其他头脑风暴的建议也将不胜感激。谢谢！

Answer 1

您可以通过二进制模式打开文件来读取原始字节：

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

然后您可以读取一些数据：

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

其中p 是指向某个缓冲区的指针。在这种情况下，您可能希望 p 的类型为 uint8_t *，因为您主要处理的是原始字节。

或者，您可以这样在文件中跳转：

fseek(fid, pos, SEEK_SET);

我希望这足以让你继续前进。

Answer 2

您将需要一个指向文件的字节地址 22 和 18 的指针。指向这些地址后，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。