bfSize问题(Pset3,任务调整大小,CS50)

问题描述 投票:0回答:2

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;
}
c resize cs50 bmp
2个回答
0
投票
//BITMAPFILEHEADER
bf_out.bfSize = bi_out.biSizeImage - sizeof(BITMAPFILEHEADER) - sizeof(BITMAPINFOHEADER);

文件大小是图像大小plus标头的大小。不减。

您可以替换此

// 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);
}

仅需一个fread调用。无需循环。

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

0
投票

源和目标文件的填充将有所不同。使用2种不同的填充,循环中都需要它们。

int padding_in = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
int padding_out = (4 - (bi_out.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

如先前所建议,修复bfSize

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

修复biSizeImage的计算(注意括号中的更改)

bi_out.biSizeImage = abs(bi_out.biHeight) * (bi_out.biWidth * sizeof(RGBTRIPLE) + padding_in);

以二进制模式打开文件以与Windows兼容

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

如下更改循环。请注意,我们同时使用padding_inpadding_out

RGBTRIPLE *triple = malloc(bi.biWidth * sizeof(RGBTRIPLE));
for(int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
    fread(triple, sizeof(RGBTRIPLE), bi.biWidth, inptr);
    fseek(inptr, padding_in, SEEK_CUR);

    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_out; k++)
            fputc(0x00, outptr);
    }
}
free(triple);

示例

int main()
{
    int factor = 2;
    char *infile = "in.bmp";
    char *outfile = "out.bmp";

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

    BITMAPFILEHEADER bf;
    BITMAPINFOHEADER bi;
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);
    fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

    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_in = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int padding_out = (4 - (bi_out.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    bi_out.biSizeImage = abs(bi_out.biHeight) * (bi_out.biWidth * sizeof(RGBTRIPLE) + padding_in);
    bf_out.bfSize = bi_out.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    fwrite(&bf_out, sizeof(BITMAPFILEHEADER), 1, outptr);
    fwrite(&bi_out, sizeof(BITMAPINFOHEADER), 1, outptr);

    RGBTRIPLE *triple = malloc(bi.biWidth * sizeof(RGBTRIPLE));
    for(int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        fread(triple, sizeof(RGBTRIPLE), bi.biWidth, inptr);
        fseek(inptr, padding_in, SEEK_CUR);

        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_out; k++)
                fputc(0x00, outptr);
        }
    }
    free(triple);

    fclose(inptr);
    fclose(outptr);
    return 0;
}
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