Question

我目前正在参加CS50课程，而且我完全坚持调整大小问题（不太舒服）。分配是创建一个带有输入.bmp文件的程序，将其缩放n次并将其写入输出.bmp文件。但我的代码只是扭曲了输入图像，并没有改变大小。这是为测试提供的bmp（3x3像素，只是放大了这里）：https://imgur.com/1v55tjz 当我试图调整它时，它只是转向这个（仍然是3x3）：https://imgur.com/JAKQMfY

这是调整大小的代码：

这是bmp.h文件：

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

#include "bmp.h"

int main(int argc, char *argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        fprintf(stderr, "Usage: ./copy infile outfile\n");
        return 1;
    }

    // remember filenames
    int n = atoi(argv[1]);
    char *infile = argv[2];
    char *outfile = argv[3];

    // open input file
    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 2;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 3;
    }

    // read infile's BITMAPFILEHEADER
    BITMAPFILEHEADER bf;
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

    // read infile's BITMAPINFOHEADER
    BITMAPINFOHEADER bi;
    fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);


    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 ||
        bi.biBitCount != 24 || bi.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 4;
    }

    // create file- and infoheader for output file
    BITMAPFILEHEADER outBF = bf;
    BITMAPINFOHEADER outBI = bi;

    //Scale width and height by n
    outBI.biWidth *= n;
    outBI.biHeight *= n;

    //Calculate padding for input and output file
    int outPadding = (4 - (outBI.biWidth * sizeof(RGBTRIPLE) % 4) % 4);
    int inPadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //Calculate biSizeImage and bfSize for output file
    outBI.biSizeImage = ((sizeof(RGBTRIPLE) * outBI.biWidth) + outPadding * abs(outBI.biHeight));
    outBF.bfSize = outBI.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    // write outfile's BITMAPFILEHEADER
    fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);

    // write outfile's BITMAPINFOHEADER
    fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);

    //Instantiate two counters to keep track of whether we have reached the n - 1 times of the recopy method and to be able to fseek to the next line
    int countIterations = 1;
    int countPositionInFile = 0;


    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        countIterations = 1;
        for(int j = 0; j < n; j++)
        {
            // iterate over pixels in scanline
            for (int k = 0; k < bi.biWidth; k++)
            {
                // temporary storage
                RGBTRIPLE triple;

                // read RGB triple from infile
                fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

                // resize horizontally by writing every pixel in row n times
                for(int l = 0; l < n; l++)
                {
                    // write RGB triple to outfile
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }

            // skip over padding, if any
            fseek(inptr, inPadding, SEEK_CUR);

            //Add padding for this line
            for (int l = 0; l < outPadding; l++)
            {
            fputc(0x00, outptr);
            }

            if(countIterations == n)
            {
                countPositionInFile++;
            }

            int newPosition = (sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + (countPositionInFile * (bi.biWidth + inPadding)));

            // return the "cursor" to the start of the file
            fseek(inptr, newPosition, SEEK_SET);
            countIterations++;
        }

    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}

我希望有人有这项任务的经验，可以提供帮助，我现在感觉很困难，但也许我只是盯着它看了太久。提前谢谢！

Answer 1

应使用二进制标志打开文件：

FILE *inptr = fopen(infile, "rb");
FILE *outptr = fopen(outfile, "wb");

您忽略了outBI和outBF，您正在将旧标头写入新文件中：

fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);//old header
fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);//old header

这里使用两种不同的方法来计算填充：

int outPadding = (4 - (outBI.biWidth * sizeof(RGBTRIPLE)  % 4) % 4);
int inPadding =  (4 - (bi.biWidth *    sizeof(RGBTRIPLE)) % 4) % 4;
                                                        ^         ^

除了偶然之外，它们不可能都是正确的。在这种情况下，我们使用24位图，您可以将填充计算为

int outPadding = outBI.biWidth % 4;
int inPadding = bi.biWidth % 4;

这将与您使用fseek(inptr, inPadding, SEEK_CUR);和for(...) fputc(0x00, outptr);

跳过填充的方式相匹配

我无法弄清楚这段代码：

int newPosition = (sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) 
    + (countPositionInFile * (bi.biWidth + inPadding)));<==remove
fseek(inptr, newPosition, SEEK_SET);<==remove

那应该是(bi.biWidth * 3)或者您可以删除它并使用ftell在开始阅读该行之前保存位置，然后使用fseek返回该位置。< / p>

位图高度应该从下到上读取，但在这种情况下，它没有什么区别。

无法正确调整.bmp图像大小（CS50 pset 4，调整大小，不太舒服）

1 个答案: