Question

任务是将bmp图像缩放为一个因子。我的代码直观地工作，当我检查缩放后的图片的十六进制且大小正确时，它看起来是正确的，但是check50表示图片太大。我通过下载图片检查了大小，并通过CS50 IDE查看了十六进制。我还尝试了GitHub上的其他代码，但该代码也被Check50拒绝。有什么错误？预先感谢！

    // Copies a BMP file

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

#include "bmp.h"

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

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

    if(factor < 0 || factor > 100)
    {
        printf("facor must be between 0 and 100\n");
        return 15;
    }

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

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        printf("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);
        printf("Unsupported file format.\n");
        return 4;
    }

    //adjust fileheader
    BITMAPFILEHEADER bf_out = bf;
    BITMAPINFOHEADER bi_out = bi;

    //HEIGHT AND WIDTH
    bi_out.biWidth = bi.biWidth * factor;
    bi_out.biHeight = bi.biHeight * factor;

    // determine padding for scanlines
    int padding = (4 - (bi_out.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //IMAGESIZE
    bi_out.biSizeImage = bi_out.biHeight * bi_out.biWidth * sizeof(RGBTRIPLE)+ padding;

    //BITMAPFILEHEADER
    bf_out.bfSize = bi_out.biSizeImage - sizeof(BITMAPFILEHEADER) - sizeof(BITMAPINFOHEADER);


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

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

    printf("Original bfSize: %d\n", bf.bfSize);
    printf("Resized bfSize: %d\n", bf_out.bfSize);
    printf("Bitmapinfoheader: %lu\n", sizeof(BITMAPINFOHEADER));
    printf("Bitmapfileheader: %lu\n", sizeof(BITMAPFILEHEADER));
    printf("Original biSizeImage: %d\n", bi.biSizeImage);
    printf("Resized biSizeImage: %d\n", bi_out.biSizeImage);
    printf("Original biWidth: %d\n", bi.biWidth);
    printf("Original biHeight: %d\n", bi.biHeight);
    printf("Resized biWidth: %d\n", bi_out.biWidth);
    printf("Resized biHeight: %d\n", bi_out.biHeight);

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        // temporary storage
        RGBTRIPLE triple[bi.biWidth];
        // iterate over pixels in scanline
        for (int j = 0; j < bi.biWidth; j++)
        {
            // read RGB triple from infile
            fread(&triple[j], sizeof(RGBTRIPLE), 1, inptr);
        }
        for(int l = 0; l < factor; l++)
        {
            for(int o = 0; o < bi.biWidth; o++)
            {
                for(int g = 0; g < factor; g++)
                {
                    fwrite(&triple[o], sizeof(RGBTRIPLE), 1, outptr);
                }
            }
            for (int k = 0; k < padding; k++)
            {
                fputc(0x00, outptr);
            }
        }
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}

Answer 1

//BITMAPFILEHEADER
bf_out.bfSize = bi_out.biSizeImage - sizeof(BITMAPFILEHEADER) - sizeof(BITMAPINFOHEADER);

文件大小是图片大小加标题大小。不是负数。

您可以替换它

// temporary storage
RGBTRIPLE triple[bi.biWidth];
// iterate over pixels in scanline
for (int j = 0; j < bi.biWidth; j++)
{
    // read RGB triple from infile
    fread(&triple[j], sizeof(RGBTRIPLE), 1, inptr);
}

仅需一次fread调用。无需循环。

RGBTRIPLE triple[bi.biWidth];
fread(triple, sizeof(RGBTRIPLE), bi.biWidth, inptr);

您还需要计算原始图像的填充，然后在读入缓冲区后查找过去。

Answer 2

在网上寻找解决方案后，我终于设法找到了一个我也能理解的代码。也许它将帮助有类似问题的人。此解决方案适用于while循环而不是for循环，并且填充是在内部循环之外完成的，尽管代码几乎相同。

v[1]=NA
func(v,na.rm=T)

bfSize问题（Pset3，任务调整大小，CS50）

2 个答案: