C的新手一直在用我的代码调整24位未压缩位图的大小。我试图将这个图像缩小n倍，我觉得我接近它正常工作，但我输出的图像仍然不正确。
我可以发布输入24位未压缩BMP（small.bmp）的图片我用于测试，我的程序正在输出的图片（resized.bmp），以及由一个因子缩放的small.bmp的正确图像4应该看起来像，如果这将是有帮助的。请问。
resize.c
#include <stdio.h>
#include <stdlib.h>
#include "bmp.h"
int main(int argc, char *argv[])
{
// ensure proper usage
if (argc != 4)
{
fprintf(stderr, "Usage: ./resize scale infile outfile\n");
return 1;
}
int n = atoi(argv[1]);
// remember filenames
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 = bi.biWidth * n;
bi.biHeight = bi.biHeight * n;
// determine padding for scanlines
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) * abs(bi.biHeight);
bf.bfSize = bi.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);
// iterate over infile's scanlines
for (int i = 0, biHeight = abs(oldHeight); i < biHeight; i++)
{
// store scanline in an array pixel by pixel for vertical scaling.
RGBTRIPLE scanline[bi.biWidth - 1];
// iterate over pixels in scanline
for (int j = 0; j < bi.biWidth; j++)
{
//check if we've hit padding in original bmp.
if (j % oldpadding == 0 && j != 0)
{
//skip the padding.
fseek(inptr, oldpadding, SEEK_CUR);
}
// temporary storage
RGBTRIPLE triple;
fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
for (int h = 0; h < n; h++)
{
//scale horizontally, save each scanline pixel to our array.
scanline[j] = triple;
}
}
for (int x = 0; x < n; x++)
{
//write scanlines n - 1 times.
for (int y = 0; y < bi.biWidth; y++)
{
fwrite(&scanline[y], sizeof(RGBTRIPLE), 1, outptr);
}
//write padding if any for current scanline.
for (int z = 0; z < padding; z++)
{
fputc(0x00, outptr);
}
}
}
// close infile
fclose(inptr);
// close outfile
fclose(outptr);
// success
return 0;
}
bmp.h
/**
* BMP-related data types based on Microsoft's own.
*/
#include <stdint.h>
/**
* Common Data Types
*
* The data types in this section are essentially aliases for C/C++
* primitive data types.
*
* Adapted from https://msdn.microsoft.com/en-us/library/cc230309.aspx.
* See http://en.wikipedia.org/wiki/Stdint.h for more on stdint.h.
*/
typedef uint8_t BYTE;
typedef uint32_t DWORD;
typedef int32_t LONG;
typedef uint16_t WORD;
/**
* BITMAPFILEHEADER
*
* The BITMAPFILEHEADER structure contains information about the type, size,
* and layout of a file that contains a DIB [device-independent bitmap].
*
* Adapted from 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;
/**
* BITMAPINFOHEADER
*
* The BITMAPINFOHEADER structure contains information about the
* dimensions and color format of a DIB [device-independent bitmap].
*
* Adapted from 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;
/**
* RGBTRIPLE
*
* This structure describes a color consisting of relative intensities of
* red, green, and blue.
*
* Adapted from https://msdn.microsoft.com/en-us/library/dd162939(v=vs.85).aspx.
*/
typedef struct
{
BYTE rgbtBlue;
BYTE rgbtGreen;
BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;
答案 0 :(得分：1)
您的代码混合了两种缩放技术：1）在数组中缩放然后将其写出来; 2）在写出数据时，读取数组中的原始大小和缩放。但是，您对第一种技术的实现并没有实际进行任何缩放：
for (int h = 0; h < n; h++)
{
//scale horizontally, save each scanline pixel to our array.
scanline[j] = triple;
}
因为你没有增加j，所以你只需要将相同的三倍重叠到相同的位置n次。它根本不做任何缩放。我建议放弃第一种技术，只关注第二种技术。对于初学者，修复你的数组声明：
RGBTRIPLE scanline[bi.biWidth];
然后当你读入时，只需将三元组写入正确的位置而不进行任何循环：
scanline[j] = triple;
当你把它写出来时，你的循环就会出错了。你想循环像素并将每个像素写出n次，而不是在图像上循环n次并写出所有像素（这将重复图像n次而不是按n缩放）。然后将这个全部包装在循环中以输出每一行n次。
for (int y = 0; y < n; y++) // repeat each row n times
{
for (int x = 0; x < bi.biWidth; x++) // iterate over pixels
{
for (int r = 0; r < n; r++) // repeat each pixel n times
fwrite(&scanline[x], sizeof(RGBTRIPLE), 1, outptr);
}
// write padding if any for current scanline.
for (int z = 0; z < padding; z++)
{
fputc(0x00, outptr);
}
}
这是缩放图像的基本算法。您可以通过执行块I / O读取和写入来提高速度，而不是在循环中调用fwrite，但正如您在注释中指出的那样，正确性＆gt;效率。你可能也有一些填充问题，我还没有解决这个问题。