c - 如何在 C 中调整位图 (BMP) 的大小 - 我的代码不起作用

Question

我一直在尝试修复此代码。根据我添加的 printf 测试，一切似乎都工作正常，但新图像没有水平调整大小。

这是我正在学习的在线类(class)，因此编码可能看起来很简单，但我们可能还没有涵盖更高级的解决方案。

我已经粘贴了执行该程序所需的两个程序，并且还包括了图片。

使用此参数或类似的参数执行程序./copy 2 Staff.bmp large.bmp。

// 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)
    {
        fprintf(stderr, "Usage: copy infile outfile\n");
        return 1;
    }


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

    if (num < 1 || num > 100)
    {
        fprintf(stderr, "Resize only 1-100. Try again.\n");
        return 4;
    }

    // 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;
    }

    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    printf("padding%i ", padding);

    BITMAPINFOHEADER newbi = bi;
    BITMAPFILEHEADER newbf = bf;

    newbi.biWidth = bi.biWidth * num;
    printf("newbiwidth%i ", newbi.biWidth);

    newbi.biHeight = bi.biHeight * num;
    printf("newbiheight%i ", newbi.biHeight);

    // determine padding for scanlines
    int newpadding = (4 - (newbi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    printf("newpadding%i ", newpadding);

    newbi.biSizeImage = (newbi.biWidth * sizeof(RGBTRIPLE) + newpadding) * abs(newbi.biHeight);
    printf("newbisizeimage%i ", newbi.biSizeImage);

    newbf.bfSize = newbi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
    printf("newbfsize%i ", newbf.bfSize);

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

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



    // temporary storage
    RGBTRIPLE triple;
    RGBTRIPLE *newtriple = malloc(num * sizeof(RGBTRIPLE) + 1);
    RGBTRIPLE *sline = malloc(newbi.biWidth * sizeof(RGBTRIPLE));

    // read RGB triple from infile
    for (int i = 0, biheight = abs(bi.biHeight); i < biheight; i++)
    {
        printf("H%i  ", i);
        for (int j = 0; j < bi.biWidth; j++)
        {
            printf("W%i  ", j);
            fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

            //store triple times resize number
            for (int m = 0; m < num; m++)
            {
                newtriple[m] = triple;
                printf("T%i  ", m);
            }

                    //store new triple as new scanline
                    sline[j] = *newtriple;
                    printf("S%i  ", j);
        }

            //write new scanline to file
            for (int k = 0; k < num; k++)
            {
                printf("F%i  ", k);
                fwrite(sline, newbi.biWidth * 3, 1, outptr);

                // add padding if any
                for (int h = 0; h < newpadding; h++)
                {
                    fputc(0x00, outptr);
                }

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

    }
    free(newtriple);
    free(sline);

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);


    // success
    return 0;
}

// BMP-related data types based on Microsoft's own

#include <stdint.h>

// aliases for C/C++ primitive data types
// https://msdn.microsoft.com/en-us/library/cc230309.aspx
typedef uint8_t  BYTE;
typedef uint32_t DWORD;
typedef int32_t  LONG;
typedef uint16_t WORD;

// information about the type, size, and layout of a file
// https://msdn.microsoft.com/en-us/library/dd183374(v=vs.85).aspx
typedef struct
{
    WORD bfType;
    DWORD bfSize;
    WORD bfReserved1;
    WORD bfReserved2;
    DWORD bfOffBits;
} __attribute__((__packed__))
BITMAPFILEHEADER;

// information about the dimensions and color format
// https://msdn.microsoft.com/en-us/library/dd183376(v=vs.85).aspx
typedef struct
{
    DWORD biSize;
    LONG biWidth;
    LONG biHeight;
    WORD biPlanes;
    WORD biBitCount;
    DWORD biCompression;
    DWORD biSizeImage;
    LONG biXPelsPerMeter;
    LONG biYPelsPerMeter;
    DWORD biClrUsed;
    DWORD biClrImportant;
} __attribute__((__packed__))
BITMAPINFOHEADER;

// relative intensities of red, green, and blue
// https://msdn.microsoft.com/en-us/library/dd162939(v=vs.85).aspx
typedef struct
{
    BYTE rgbtBlue;
    BYTE rgbtGreen;
    BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;

Answer 1

for (int j = 0; j < bi.biWidth; j++)
{
    ...
    sline[j] = *newtriple;
}

这只是为每行设置从 0 到原始宽度的像素。例如，如果将宽度加倍，则图像的右后半部分不会初始化，这就是输出图像中出现的内容。您应该如下所示设置所有像素。你实际上并不需要newtriple

还要确保在读取每一行后立即跳过填充。

for(int j = 0; j < bi.biWidth; j++)
{
    fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
    for(int m = 0; m < num; m++)
    {
        sline[j * num + m] = triple;
    }
    //sline[j] = *newtriple; <- remove
}
fseek(inptr, padding, SEEK_CUR); //<- move fseek here

什么sline[j * num + m]正在做:

假设我们有这一行:

sline_in[4]: 0 1 2 3 4

我们想要以 2 倍放大。它应该变成:

sline_out[8]: 0 0 1 1 2 2 3 3 4 4

我们使用循环:

for(int j = 0; j < width; j++)
{
    sline_out[j * 2 + 0] = sline_in[j];
    sline_out[j * 2 + 1] = sline_in[j];
}

对于任意缩放系数，我们使用以下内容:

for(int j = 0; j < width; j++)
{
    for(int m = 0; m < zoom; m++)
        sline_out[j * zoom + m] = sline_in[j];
}