C/C++编程：C生成BMP、PNG和JPEG图片:

小咪咪 2023-03-12 14:26 37阅读 0赞

# 1、生成bmp图片 #

在学习图形图像的过程中，最简单和常见的格式是BMP和PPM。下面将给出生成BMP的极度精简代码，然后讲解BMP格式。

#include <stdio.h>
    #include <stdlib.h>
    #define w 200
    #define h 200
    void WriteBMP(char*img,const char* filename)
    {
        
        int l=(w*3+3)/4*4;
        int bmi[]= {
        l*h+54,0,54,40,w,h,1|3*8<<16,0,l*h,0,0,100,0};
        FILE *fp = fopen(filename,"wb");
        fprintf(fp,"BM");
        fwrite(&bmi,52,1,fp);
        fwrite(img,1,l*h,fp);
        fclose(fp);
    }
    int main()
    {
        
        char img[w*h*3];
        for(int i=0; i<w*h*3; i++)img[i]=rand()%256;
        WriteBMP(img,"test.bmp");
        system("test.bmp");
        return 0;
    }

上述代码生成一幅宽和高均为200的BMP随机位图。如图所示：  
![在这里插入图片描述][20200509092816136.png]

# 2、生成png图片 #

生成无压缩PNG图片：[https://github.com/miloyip/svpng][https_github.com_miloyip_svpng]

//------------------ svpng.h---------------------
    
    /*! \file
        \brief      svpng() is a minimalistic C function for saving RGB/RGBA image into uncompressed PNG.
        \author     Milo Yip
        \version    0.1.1
        \copyright  MIT license
        \sa         http://github.com/miloyip/svpng
    */
    
    #ifndef SVPNG_INC_
    #define SVPNG_INC_
    
    /*! \def SVPNG_LINKAGE
        \brief User customizable linkage for svpng() function.
        By default this macro is empty.
        User may define this macro as static for static linkage,
        and/or inline in C99/C++, etc.
    */
    #ifndef SVPNG_LINKAGE
    #define SVPNG_LINKAGE
    #endif
    
    /*! \def SVPNG_OUTPUT
        \brief User customizable output stream.
        By default, it uses C file descriptor and fputc() to output bytes.
        In C++, for example, user may use std::ostream or std::vector instead.
    */
    #ifndef SVPNG_OUTPUT
    #include <stdio.h>
    #define SVPNG_OUTPUT FILE* fp
    #endif
    
    /*! \def SVPNG_PUT
        \brief Write a byte
    */
    #ifndef SVPNG_PUT
    #define SVPNG_PUT(u) fputc(u, fp)
    #endif
    
    
    /*!
        \brief Save a RGB/RGBA image in PNG format.
        \param SVPNG_OUTPUT Output stream (by default using file descriptor).
        \param w Width of the image. (<16383)
        \param h Height of the image.
        \param img Image pixel data in 24-bit RGB or 32-bit RGBA format.
        \param alpha Whether the image contains alpha channel.
    */
    SVPNG_LINKAGE void svpng(SVPNG_OUTPUT, unsigned w, unsigned h, const unsigned char* img, int alpha) {
        
        static const unsigned t[] = {
         0, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
                /* CRC32 Table */    0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c, 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c };
        unsigned a = 1, b = 0, c, p = w * (alpha ? 4 : 3) + 1, x, y, i;   /* ADLER-a, ADLER-b, CRC, pitch */
    #define SVPNG_U8A(ua, l) for (i = 0; i < l; i++) SVPNG_PUT((ua)[i]);
    #define SVPNG_U32(u) do { SVPNG_PUT((u) >> 24); SVPNG_PUT(((u) >> 16) & 255); SVPNG_PUT(((u) >> 8) & 255); SVPNG_PUT((u) & 255); } while(0)
    #define SVPNG_U8C(u) do { SVPNG_PUT(u); c ^= (u); c = (c >> 4) ^ t[c & 15]; c = (c >> 4) ^ t[c & 15]; } while(0)
    #define SVPNG_U8AC(ua, l) for (i = 0; i < l; i++) SVPNG_U8C((ua)[i])
    #define SVPNG_U16LC(u) do { SVPNG_U8C((u) & 255); SVPNG_U8C(((u) >> 8) & 255); } while(0)
    #define SVPNG_U32C(u) do { SVPNG_U8C((u) >> 24); SVPNG_U8C(((u) >> 16) & 255); SVPNG_U8C(((u) >> 8) & 255); SVPNG_U8C((u) & 255); } while(0)
    #define SVPNG_U8ADLER(u) do { SVPNG_U8C(u); a = (a + (u)) % 65521; b = (b + a) % 65521; } while(0)
    #define SVPNG_BEGIN(s, l) do { SVPNG_U32(l); c = ~0U; SVPNG_U8AC(s, 4); } while(0)
    #define SVPNG_END() SVPNG_U32(~c)
        SVPNG_U8A("\x89PNG\r\n\32\n", 8);           /* Magic */
        SVPNG_BEGIN("IHDR", 13);                    /* IHDR chunk { */
        SVPNG_U32C(w); SVPNG_U32C(h);               /*   Width & Height (8 bytes) */
        SVPNG_U8C(8); SVPNG_U8C(alpha ? 6 : 2);     /*   Depth=8, Color=True color with/without alpha (2 bytes) */
        SVPNG_U8AC("\0\0\0", 3);                    /*   Compression=Deflate, Filter=No, Interlace=No (3 bytes) */
        SVPNG_END();                                /* } */
        SVPNG_BEGIN("IDAT", 2 + h * (5 + p) + 4);   /* IDAT chunk { */
        SVPNG_U8AC("\x78\1", 2);                    /*   Deflate block begin (2 bytes) */
        for (y = 0; y < h; y++) {
                           /*   Each horizontal line makes a block for simplicity */
            SVPNG_U8C(y == h - 1);                  /*   1 for the last block, 0 for others (1 byte) */
            SVPNG_U16LC(p); SVPNG_U16LC(~p);        /*   Size of block in little endian and its 1's complement (4 bytes) */
            SVPNG_U8ADLER(0);                       /*   No filter prefix (1 byte) */
            for (x = 0; x < p - 1; x++, img++)
                SVPNG_U8ADLER(*img);                /*   Image pixel data */
        }
        SVPNG_U32C((b << 16) | a);                  /*   Deflate block end with adler (4 bytes) */
        SVPNG_END();                                /* } */
        SVPNG_BEGIN("IEND", 0); SVPNG_END();        /* IEND chunk {} */
    }
    
    #endif /* SVPNG_INC_ */

-----------------main.c---------------------------------
    #include "svpng.h"
    
    void test_rgb(void) {
        
        unsigned char rgb[256 * 256 * 3], *p = rgb;
        unsigned x, y;
        FILE *fp = fopen("C:\\Users\\Administrator\\Pictures\\rgb.png", "wb");
        for (y = 0; y < 256; y++)
            for (x = 0; x < 256; x++) {
        
                *p++ = (unsigned char)x;    /* R */
                *p++ = (unsigned char)y;    /* G */
                *p++ = 128;                 /* B */
            }
        svpng(fp, 256, 256, rgb, 0);
        fclose(fp);
    }
    
    void test_rgba(void) {
        
        unsigned char rgba[256 * 256 * 4], *p = rgba;
        unsigned x, y;
        FILE* fp = fopen("C:\\Users\\Administrator\\Pictures\\rgba.png", "wb");
        for (y = 0; y < 256; y++)
            for (x = 0; x < 256; x++) {
        
                *p++ = (unsigned char)x;                /* R */
                *p++ = (unsigned char)y;                /* G */
                *p++ = 128;                             /* B */
                *p++ = (unsigned char)((x + y) / 2);    /* A */
            }
        svpng(fp, 256, 256, rgba, 1);
        fclose(fp);
    }
    
    int main(void) {
        
        test_rgb();
        test_rgba();
        return 0;
    }

补充：LodePNG是一个集合了PNG图像解码器和编码器的代码文件，不依赖于诸如zlib和libpng的外部链接/库，提供方便友好的PNG编解码器调用方法。LodePNG主要是采用C（ISO C90）编写的，并提供了C++的接口。LodePNG的使用非常简单，只要在项目文件中包含lodepng.cpp和lodepng.h或者lodepng.c和lodepng.h就可以。

[20200509092816136.png]: /images/20230312/e574c478a2064a99ba22d84c01b9dafc.png
[https_github.com_miloyip_svpng]: https://github.com/miloyip/svpng