原理: R=RxR/255, G=GxG/255, B=BxB/255.

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.实现暗黑色彩效果算法

int DarkColorImage(ImagePicData *ImageData)
{
    ImageRGBAColor RGBAColor;
    int Height = ImageData->Height;
    int Width = ImageData->Width;
    int Pos = 0;
    int i, j;

    for(i=0; i<Height; i++)
    {
        for(j=0; j<Width; j++)
        {
            RGBAColor.r = ImageData->RGBA[((i)*Width+(j))*4+0] * ImageData->RGBA[((i)*Width+(j))*4+0] / 255;
            RGBAColor.g = ImageData->RGBA[((i)*Width+(j))*4+1] * ImageData->RGBA[((i)*Width+(j))*4+1] / 255;
            RGBAColor.b = ImageData->RGBA[((i)*Width+(j))*4+2] * ImageData->RGBA[((i)*Width+(j))*4+2] / 255;

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

            ImageData->RGBA[((i)*Width+(j))*4+0] = RGBAColor.r;
            ImageData->RGBA[((i)*Width+(j))*4+1] = RGBAColor.g;
            ImageData->RGBA[((i)*Width+(j))*4+2] = RGBAColor.b;
        }
    }

    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;
    char RGBAData[16*300*300];
    char JpegInputName[256];
    char JpegOutputName[256];

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

    if(argc != 3)
    {
        printf("入参个数错误!\n");
        return -1;
    }

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

    PicData.RGBA = RGBAData;

    strcpy(PicData.FName, JpegInputName);

    LoadJPG(&PicData);

    strcpy(PicData.FName, JpegOutputName);

    DarkColorImage(&PicData);

    CreateJPG(&PicData);

    return 0;
}

5.编译运行

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

6.运行结果

原图

a.jpg

效果

b.jpg