调整 bmp 图像大小

Posted 2023-02-16

【中文标题】调整 bmp 图像大小

【英文标题】：Resizing bmp image

【发布时间】：2020-10-29 14:30:09

【问题描述】：

我正在尝试调整 bmp 图像的大小，它几乎可以工作，但由于某种原因，我得到了用零填充的额外字节。它有点工作，但我想知道这些零是从哪里来的。

我不确定它是否与那些零以某种方式连接，但有时图像深度 (biBitCount) 从原始文件中的 24 变为 32。我无法弄清楚为什么会这样。不幸的是，我没有保存那个截图。

我敢肯定，我只是犯了一些我看不到的愚蠢错误。请帮帮我。 original bmp double sized bmp with extra zeros

我的代码：

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

#include "bmp.h"

float atoi2_0(char* S);

int main(int argc, char *argv[])

    // ensure proper usage
    if (argc != 4)
    
        fprintf(stderr, "Usage: ./resize f infile outfile\n");
        return 1;
    

    // remember filenames
    float f = atoi2_0(argv[1]);
    if(f == -1 || f <= 0.0 || f > 100)
    
        printf("Usage: ./resize f infile outfile\n");
        return 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;
    

    int oldpadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    bi.biWidth *= f;
    bi.biHeight *= f;

    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) * abs(bi.biHeight);
    bf.bfSize = bi.biSizeImage + 54;


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

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

float df = f - (int)f;
int revdf = 1 / df;
int bbw = bi.biWidth / f;

for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)

    RGBTRIPLE * oldtriple = (RGBTRIPLE*)calloc(bbw, sizeof(RGBTRIPLE));
    if (oldtriple == NULL)
    
        fclose(inptr);
        fclose(outptr);
        return 5;
    

    fread(oldtriple, sizeof(RGBTRIPLE), bbw, inptr);

    RGBTRIPLE * triple = (RGBTRIPLE*)calloc(bi.biWidth, sizeof(RGBTRIPLE));
    if (triple == NULL)
    
        free(oldtriple);
        fclose(inptr);
        fclose(outptr);
        return 5;
    

    for (int j = 0; j < bbw; j++)
    
        int jxf = j * f;
        for (int n = 0; n < f; n++)
        
            *(triple + jxf + n) = *(oldtriple + j);
        
    


    for (int j = 0; j < f; j++)
    
        if (i % revdf && f - j == df) continue;
        fwrite(triple, sizeof(RGBTRIPLE), bi.biWidth, outptr);
        for (int n = 0; n < padding; n++)
        
            fputc(0x00, outptr);
        
    

    fseek(inptr, oldpadding, SEEK_CUR);

    free(triple);
    free(oldtriple);


    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;


float atoi2_0(char* S)//kinda atoi for floats

    int strl = strlen(S);
    for (int i = 0; i < strl; i++)//input check
    
        if ((S[i] < '0' || S[i] > '9') && (S[i] != '.'))
        
            printf("Invalid input");
            return -1;
        
    
    float a = atoi(S);
    char D[10] =  0 ;
    for (int i = 0; i < strl; i++)
    
        if (S[i] == '.')
        
            ++i;
            for (int j = 0; i < strl; i++, j++)
            
                D[j] = S[i];
            
        
    
    a += (float)atoi(D) / pow(10, strlen(D));
    return a;






BMP.h :

``` // 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;

【问题讨论】：

您知道stdlib.h 包含atoi 和atof 吗？

不，我不知道，但这不是什么大问题。

【参考方案1】：

是的，我自己修好了。问题在于周期长度。