原理: 当A<128时, C=AxB/128, 当A>128时, C=255-(255-A)x(255-B)/128.

1.添加头文件, 并定义相关宏和结构体

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

#define JpegStdError jpeg_std_error
#define JpegCreateDecompress jpeg_create_decompress
#define JpegCreateCompress jpeg_create_compress
#define JpegStdioSrc jpeg_stdio_src
#define JpegReadHeader jpeg_read_header
#define JpegStartDecompress jpeg_start_decompress
#define ScanLine output_scanline
#define NextLine next_scanline
#define JpegReadLine jpeg_read_scanlines
#define JpegFinishDecompress jpeg_finish_decompress
#define JpegDestroyDecompress jpeg_destroy_decompress
#define JpegStdioDest jpeg_stdio_dest
#define JpegSetDefault jpeg_set_defaults
#define JpegSetQuality jpeg_set_quality
#define JpegStartCompress jpeg_start_compress
#define JpegWriteLine jpeg_write_scanlines
#define JpegFinishCompress jpeg_finish_compress
#define JpegDestroyCompress jpeg_destroy_compress

typedef JSAMPARRAY JpegArray;
typedef FILE *FilePtr;
typedef struct jpeg_compress_struct JpegComp;
typedef struct jpeg_decompress_struct JpegDecomp;
typedef struct jpeg_error_mgr JpegErrMgr;
typedef struct ImagePicData ImagePicData;
typedef struct ImageRGBAColor ImageRGBAColor;

struct ImagePicData
{
    unsigned char FName[256];
    FilePtr FPtr;
    int Width;
    int Height;
    int BitDepth;
    int Flag;
    int ColType;
    unsigned char *RGBA;
};

struct ImageRGBAColor
{
    short r;
    short g;
    short b;
    short a;
};

2.实现叠加效果算法

int CompositeImage(ImagePicData *ImageDataA, ImagePicData *ImageDataB)
{
    ImageRGBAColor a, b, c;
    int Height = ImageDataA->Height;
    int Width = ImageDataA->Width;
    int Pos = 0;
    int i, j;

    for(i=0; i<Height; i++)
    {
        for(j=0; j<Width; j++)
        {
            a.r = ImageDataA->RGBA[Pos*4+0];
            a.g = ImageDataA->RGBA[Pos*4+1];
            a.b = ImageDataA->RGBA[Pos*4+2];

            b.r = ImageDataB->RGBA[Pos*4+0];
            b.g = ImageDataB->RGBA[Pos*4+1];
            b.b = ImageDataB->RGBA[Pos*4+2];

            if(a.r < 128)
            {
                c.r = b.r * a.r / 128;
            }
            else
            {
                c.r = 255 - (255-b.r) * (255-a.r) / 128;
            }

            if(a.g < 128)
            {
                c.g = b.g * a.g / 128;
            }
            else
            {
                c.g = 255 - (255-b.g) * (255-a.g) / 128;
            }

            if(a.b < 128)
            {
                c.b = b.b * a.b / 128;
            }
            else
            {
                c.b = 255 - (255-b.b) * (255-a.b) / 128;
            }

            if(c.r > 255) c.r = 255;
            else if(c.r < 0) c.r = 0;
            if(c.g > 255) c.g = 255;
            else if(c.g < 0) c.g = 0;
            if(c.b > 255) c.b = 255;
            else if(c.b < 0) c.b = 0;

            ImageDataA->RGBA[Pos*4+0] = c.r;
            ImageDataA->RGBA[Pos*4+1] = c.g;
            ImageDataA->RGBA[Pos*4+2] = c.b;

            Pos++;
        }
    }

    return 0;
}

3.读写图片

参见《C语言实现色彩平衡算法》

4.添加主函数

int main(int argc, char **argv)
{
    ImagePicData PicData[2];
    char RGBAData[2][16*300*300];
    char TmpData[16*300*300];
    char JpegInputName[2][256];
    char JpegOutputName[256];

    memset(PicData, 0x00, sizeof(PicData));
    memset(TmpData, 0x00, sizeof(TmpData));
    memset(JpegInputName, 0x00, sizeof(JpegInputName));
    memset(JpegOutputName, 0x00, sizeof(JpegOutputName));

    if(argc != 4)
    {
        printf("入参个数错误!\n");
        return -1;
    }

    strncpy(JpegInputName[0], argv[1], 255);
    strncpy(JpegInputName[1], argv[2], 255);
    strncpy(JpegOutputName, argv[3], 255);

    PicData[0].RGBA = RGBAData[0];
    PicData[1].RGBA = RGBAData[1];

    strcpy(PicData[0].FName, JpegInputName[0]);
    strcpy(PicData[1].FName, JpegInputName[1]);

    LoadJPG(PicData);
    LoadJPG(PicData+1);

    strcpy(PicData[0].FName, JpegOutputName);

    CompositeImage(PicData, PicData+1);

    CreateJPG(PicData);

    return 0;
}

5.编译运行

$ gcc -o examle examle.c -L$HOME/local/prior/lib -ljpeg 
$ ./examle a.jpg e.jpg p.jpg

6.运行结果

原图

a.jpg

e.jpg

效果

p.jpg