数据压缩 实验四 DPCM压缩系统的实现和分析

实验原理

DPCM是差分预测编码调制的缩写，是比较典型的预测编码系统。在DPCM系统中，需要注意的是预测器的输入是已经解码以后的样本。之所以不用原始样本来做预测，是因为在解码端无法得到原始样本，只能得到存在误差的样本。因此，在DPCM编码器中实际内嵌了一个解码器，如编码器虚线框中所示。

DPCM是差分预测编码调制的缩写，是比较典型的预测编码系统。在DPCM系统中，需要注意的是预测器的输入是已经解码以后的样本。之所以不用原始样本来做预测，是因为在解码端无法得到原始样本，只能得到存在误差的样本。因此，在DPCM编码器中实际内嵌了一个解码器，如编码器中虚线框中所示。
在一个DPCM系统中，有两个因素需要设计：预测器和量化器。理想情况下，预测器和量化器应进行联合优化。实际中，采用一种次优的设计方法：分别进行线性预测器和量化器的优化设计。

代码分析

main.cpp

#include
#include
#include
#include
#include
#include"DPCM.h"
#define u_int8_t    unsigned __int8
#define u_int       unsigned __int32
#define u_int32_t   unsigned __int32

BITMAPFILEHEADER File_header;
BITMAPINFOHEADER Info_header;

int main(int argc, char** argv)
{   
    bool flip = FALSE;                  //BMP图像倒序存储数据 需要翻转

    char* bmpFileName = NULL;           //输入
    char* yuvFileName = NULL;           //输出
    char* deviationFileName = NULL;     //误差
    char* rebuildFileName = NULL;       //重建
    FILE* bmpFile = NULL;
    FILE* yuvFile = NULL;
    FILE* deviationFile = NULL;
    FILE* rebuildFile = NULL;

    u_int8_t* rgbBuf = NULL;
    u_int8_t* yBuf = NULL;
    u_int8_t* uBuf = NULL;
    u_int8_t* vBuf = NULL;
    u_int8_t* deviationBuf = NULL;
    u_int8_t* rebuildBuf = NULL;

    u_int frameWidth, frameHeight;      //宽高
    int i = 0, j = 0;

    bmpFileName = argv[1];              //输入
    yuvFileName = argv[2];              //输出
    deviationFileName = argv[3];        //误差
    rebuildFileName = argv[4];          //重建

    /////read files/////
    bmpFile = fopen(bmpFileName, "rb");
    if (bmpFile == NULL)
    {
        printf("cannot find bmp file\n");
        exit(1);
    }
    else
    {
        printf("The input bmp file is %s\n", bmpFileName);
    }

    yuvFile = fopen(yuvFileName, "wb");
    if (yuvFile == NULL)
    {
        printf("cannot find yuv file\n");
        exit(1);
    }
    else
    {
        printf("The output yuv file is %s\n", yuvFileName);
    }

    deviationFile = fopen(deviationFileName, "wb");
    if (deviationFile == NULL)
    {
        printf("cannot find deviation file\n");
        exit(1);
    }
    else
    {
        printf("The output deviation file is %s\n", deviationFileName);
    }

    rebuildFile = fopen(rebuildFileName, "wb");
    if (rebuildFile == NULL)
    {
        printf("cannot find rebuild file\n");
        exit(1);
    }
    else
    {
        printf("The output rebuild file is %s\n", rebuildFileName);
    }
    printf("\n");
    /////read BMP fileheader & infoheader/////
    if (fread(&File_header, sizeof(BITMAPFILEHEADER), 1, bmpFile) != 1)
    {
        printf("read file header error!");
        exit(0);
    }
    if (File_header.bfType != 0x4D42)
    {
        printf("Not bmp file!");
        exit(0);
    }
    else
    {
        printf("this is a bmp file.\n");
    }
    if (fread(&Info_header, sizeof(BITMAPINFOHEADER), 1, bmpFile) != 1)
    {
        printf("read info header error!");
        exit(0);
    }
    printf("bitcount==%d\n", (unsigned char)Info_header.biBitCount);
    /////end read header/////

    frameWidth = Info_header.biWidth;               //宽高赋值
    frameHeight = Info_header.biHeight;

    /////开缓存区/////
    rgbBuf = (u_int8_t *)malloc(sizeof(u_int8_t)*frameHeight*frameWidth * 3);
    memset(rgbBuf, 0, frameHeight*frameWidth * 3);
    yBuf = (u_int8_t*)malloc(sizeof(u_int8_t)*frameHeight*frameWidth);
    uBuf = (u_int8_t*)malloc(sizeof(u_int8_t)*frameHeight*frameWidth / 4);
    vBuf = (u_int8_t*)malloc(sizeof(u_int8_t)*frameHeight*frameWidth / 4);
    deviationBuf = (u_int8_t*)malloc(sizeof(u_int8_t)*frameHeight*frameWidth);
    rebuildBuf = (u_int8_t*)malloc(sizeof(u_int8_t)*frameHeight*frameWidth);

    ReadRGB(rgbBuf, bmpFile, File_header, Info_header);
    if (RGB2YUV(frameWidth, frameHeight, rgbBuf, yBuf, uBuf, vBuf, flip))
    {
        printf("Color transferring failed");
        return 0;
    }

    printf("framewidth==%d,frameheight==%d.\n", frameWidth, frameHeight);       //输出图像宽高

    DO_DPCM(yBuf, deviationBuf, rebuildBuf,frameWidth,frameHeight);                 //进行DPCM编码

    fwrite(yBuf, 1, frameWidth * frameHeight, yuvFile);                         //写输出文件
    fwrite(deviationBuf, 1, frameHeight*frameWidth, deviationFile);
    fwrite(rebuildBuf, 1, frameHeight*frameWidth, rebuildFile);

    /////关缓存/////
    if (rgbBuf != NULL) 
        free(rgbBuf);
    if (yBuf != NULL) 
        free(yBuf);
    if (uBuf != NULL) 
        free(uBuf);
    if (vBuf != NULL) 
        free(vBuf);
    if (deviationBuf != NULL) 
        free(deviationBuf);
    if (rebuildBuf != NULL) 
        free(rebuildBuf);
    /////关文件/////
    if (bmpFile != NULL) 
        fclose(bmpFile);
    if (yuvFile != NULL) 
        fclose(yuvFile);
    if(deviationFile != NULL) 
        fclose(deviationFile);
    if(rebuildFile != NULL) 
        fclose(rebuildFile);

    system("pause");
    return 0;
}

DPCM.cpp

#include
#include
#include
#include"DPCM.h"
static float RGBYUV02990[256], RGBYUV05870[256], RGBYUV01140[256];
static float RGBYUV01684[256], RGBYUV03316[256];
static float RGBYUV04187[256], RGBYUV00813[256];

bool MakePalette(FILE * pFile, BITMAPFILEHEADER &file_h, BITMAPINFOHEADER & info_h, RGBQUAD *pRGB_out)
{
    /*若图像开始位置与INFOHEADER结束处位置，还有pow(2, info_h.biBitCount）个
    结构体RGBQUAQ的空间（颜色数为2的biBitCount次方，调色板为数组），则说明
    该bmp图像有调色板。*/
    if ((file_h.bfOffBits - sizeof(BITMAPFILEHEADER) - info_h.biSize) == sizeof(RGBQUAD)*pow(2.0, info_h.biBitCount))
    {
        fseek(pFile, sizeof(BITMAPFILEHEADER) + info_h.biSize, 0);
        fread(pRGB_out, sizeof(RGBQUAD), (unsigned int)pow(2.0, info_h.biBitCount), pFile);
        return true;
    }
    else
        return false;
}

void ReadRGB(unsigned char * rgbbuf, FILE *bmpfile, BITMAPFILEHEADER &file_h, BITMAPINFOHEADER & info_h)
{
    u_int Width = 0, Height = 0;
    long Loop = 0;
    unsigned char *bmpbuf = NULL;
    unsigned char *rgb = NULL;
    unsigned char mask = 0;
    int deltaw = 0;
    rgb = rgbbuf;

    if (((info_h.biWidth  * info_h.biBitCount / 8) % 4) == 0)
        Width = info_h.biWidth*info_h.biBitCount / 8;
    else
        Width = (info_h.biWidth  * info_h.biBitCount + 31) / 32 * 4;

    if ((info_h.biHeight % 2) == 0)
        Height = info_h.biHeight;
    else
        Height = info_h.biHeight + 1;

    deltaw = Width - info_h.biWidth * info_h.biBitCount / 8;
    bmpbuf = (unsigned char *)malloc(sizeof(unsigned char)*Height*Width);
    printf("word_width :%d , word_height: %d \n", Width, Height);
    RGBQUAD *pRGB = (RGBQUAD *)malloc(sizeof(RGBQUAD) * (unsigned int)pow(2.0, (double)info_h.biBitCount));

    if (!MakePalette(bmpfile, file_h, info_h, pRGB))
    {
        printf("No palette!\n");                        //没有调色板
    }

    fread(bmpbuf, 1, Height*Width, bmpfile);
    if (info_h.biBitCount == 24)                        //24位bmp
    {
        for (Loop = 0; Loopif (deltaw != 0)
            {
                if (deltaw == 1)
                {
                    if ((Loop + 1) % Width == 0)
                        continue;
                }
                else if (deltaw == 2)
                {
                    if ((Loop + 1) % Width == 0 || (Loop + 2) % Width == 0)
                        continue;
                }
                else
                {
                    if ((Loop + 1) % Width == 0 || (Loop + 2) % Width == 0 || (Loop + 3) % Width == 0)
                        continue;
                }
            }
            *rgb = *(bmpbuf + Loop);
            rgb++;
        }
    }
    else if (info_h.biBitCount == 16)                   //16位bmp
    {
        for (Loop = 0; Loop < Height * Width; Loop += 2)
        {
            *rgb = (bmpbuf[Loop] & 0x1F) << 3;
            *(rgb + 1) = ((bmpbuf[Loop] & 0xE0) >> 2) + ((bmpbuf[Loop + 1] & 0x03) << 6);
            *(rgb + 2) = (bmpbuf[Loop + 1] & 0x7C) << 1;
            rgb += 3;
        }
    }
    else if (info_h.biBitCount == 32)                   //32位bmp
    {
        for (Loop = 0; Loop < info_h.biWidth*info_h.biHeight; Loop++)
        {
            *(rgb + 3 * Loop) = *(bmpbuf + 4 * Loop);
            *(rgb + 3 * Loop + 1) = *(bmpbuf + 4 * Loop + 1);
            *(rgb + 3 * Loop + 2) = *(bmpbuf + 4 * Loop + 2);
        }
    }
    else                                                //其他位bmp
    {
        for (Loop = 0; Loop < Height*Width; Loop++)
        {
            if (deltaw != 0)
            {
                if (deltaw == 1)
                {
                    if ((Loop + 1) % Width == 0)
                        continue;
                }
                else if (deltaw == 2)
                {
                    if ((Loop + 1) % Width == 0 || (Loop + 2) % Width == 0)
                        continue;
                }
                else
                {
                    if ((Loop + 1) % Width == 0 || (Loop + 2) % Width == 0 || (Loop + 3) % Width == 0)
                        continue;
                }
            }
            switch (info_h.biBitCount)                  //蒙版
            {
            case 1:
                mask = 0x80;                            //10000000
                break;
            case 2:
                mask = 0xC0;                            //11000000
                break;
            case 4:
                mask = 0xF0;                            //11110000
                break;
            case 8:
                mask = 0xFF;                            //11111111
                break;
            }
            int shiftCnt = 1;
            while (mask)
            {
                /*根据从数据中提取出的索引号index，以index为调色板数组下标去查询
                数据中每info_h.biBitCount位所代表的颜色。
                while 循环的次数：
                1bit 图像 每字节循环8次
                2bit 图像 每字节循环4次
                4bit 图像 每字节循环2次
                8bit 图像 每字节循环1次。
                */
                unsigned char index =
                    mask == 0xFF ? bmpbuf[Loop] : ((bmpbuf[Loop] & mask) >> (8 - shiftCnt *info_h.biBitCount));
                *rgb = pRGB[index].rgbBlue;
                *(rgb + 1) = pRGB[index].rgbGreen;
                *(rgb + 2) = pRGB[index].rgbRed;
                if (info_h.biBitCount == 8) mask = 0;
                else    mask >>= info_h.biBitCount;
                rgb += 3;
                shiftCnt++;
            }
        }
    }
    if (pRGB != NULL) 
        free(pRGB);
    if (bmpbuf != NULL)
        free(bmpbuf);
}

int RGB2YUV(int x_dim, int y_dim, void *bmp, void *y_out, void *u_out, void *v_out, int flip)
{
    static int init_done = 0;

    long i, j, size;
    float yf, uf, vf;
    unsigned char *r, *g, *b;
    unsigned char *y, *u, *v;
    unsigned char *pu1, *pu2, *pv1, *pv2, *psu, *psv;
    unsigned char *y_buffer, *u_buffer, *v_buffer;
    unsigned char *sub_u_buf, *sub_v_buf;

    if (init_done == 0)
    {
        InitLookupTable();
        init_done = 1;
    }

    if ((x_dim % 2) || (y_dim % 2)) return 1;
    size = x_dim * y_dim;

    y_buffer = (unsigned char *)y_out;
    sub_u_buf = (unsigned char *)u_out;
    sub_v_buf = (unsigned char *)v_out;
    u_buffer = (unsigned char *)malloc(size * sizeof(unsigned char));
    v_buffer = (unsigned char *)malloc(size * sizeof(unsigned char));
    if (!(u_buffer && v_buffer))
    {
        if (u_buffer) free(u_buffer);
        if (v_buffer) free(v_buffer);
        return 2;
    }

    b = (unsigned char *)bmp;
    y = y_buffer;
    u = u_buffer;
    v = v_buffer;

    /////RGB to YUV/////
    if (!flip) 
    {
        for (j = 0; j < y_dim; j++)
        {
            y = y_buffer + (y_dim - j - 1) * x_dim;
            u = u_buffer + (y_dim - j - 1) * x_dim;
            v = v_buffer + (y_dim - j - 1) * x_dim;

            for (i = 0; i < x_dim; i++) {
                g = b + 1;
                r = b + 2;
                yf = (RGBYUV02990[*r] + RGBYUV05870[*g] + RGBYUV01140[*b]);
                uf = (-RGBYUV01684[*r] - RGBYUV03316[*g] + (*b) / 2 + 128);
                vf = ((*r) / 2 - RGBYUV04187[*g] - RGBYUV00813[*b] + 128);
                *y = (unsigned char)(yf>16 ? (yf>235 ? 235 : (unsigned char)yf) : 16);
                *u = (unsigned char)(uf>16 ? (uf>240 ? 240 : (unsigned char)uf) : 16);
                *v = (unsigned char)(vf>16 ? (vf>240 ? 240 : (unsigned char)vf) : 16);
                b += 3;
                y++;
                u++;
                v++;
            }
        }
    }
    else 
    {
        for (i = 0; i < size; i++)
        {
            g = b + 1;
            r = b + 2;
            *y = (unsigned char)(RGBYUV02990[*r] + RGBYUV05870[*g] + RGBYUV01140[*b]);
            *u = (unsigned char)(-RGBYUV01684[*r] - RGBYUV03316[*g] + (*b) / 2 + 128);
            *v = (unsigned char)((*r) / 2 - RGBYUV04187[*g] - RGBYUV00813[*b] + 128);
            b += 3;
            y++;
            u++;
            v++;
        }
    }

    for (j = 0; j < y_dim / 2; j++)
    {
        psu = sub_u_buf + j * x_dim / 2;
        psv = sub_v_buf + j * x_dim / 2;
        pu1 = u_buffer + 2 * j * x_dim;
        pu2 = u_buffer + (2 * j + 1) * x_dim;
        pv1 = v_buffer + 2 * j * x_dim;
        pv2 = v_buffer + (2 * j + 1) * x_dim;
        for (i = 0; i < x_dim / 2; i++)
        {
            *psu = (*pu1 + *(pu1 + 1) + *pu2 + *(pu2 + 1)) / 4;
            *psv = (*pv1 + *(pv1 + 1) + *pv2 + *(pv2 + 1)) / 4;
            psu++;
            psv++;
            pu1 += 2;
            pu2 += 2;
            pv1 += 2;
            pv2 += 2;
        }
    }

    free(u_buffer);
    free(v_buffer);

    return 0;
}

void InitLookupTable()
{
    int i;

    for (i = 0; i < 256; i++) RGBYUV02990[i] = (float)0.2990 * i;
    for (i = 0; i < 256; i++) RGBYUV05870[i] = (float)0.5870 * i;
    for (i = 0; i < 256; i++) RGBYUV01140[i] = (float)0.1140 * i;
    for (i = 0; i < 256; i++) RGBYUV01684[i] = (float)0.1684 * i;
    for (i = 0; i < 256; i++) RGBYUV03316[i] = (float)0.3316 * i;
    for (i = 0; i < 256; i++) RGBYUV04187[i] = (float)0.4187 * i;
    for (i = 0; i < 256; i++) RGBYUV00813[i] = (float)0.0813 * i;
}

void DO_DPCM(void * yBuf, void * deviationBuf, void *rebuildBuf, unsigned int width, unsigned int height)
{
    unsigned char *ybuffer = NULL;
    unsigned char *deviationbuffer = NULL;
    unsigned char *rebuildbuffer = NULL;
    int deviation = 0;
    int i = 0, j = 0;

    ybuffer = (unsigned char *)yBuf;                    //原始图像缓冲区
    deviationbuffer = (unsigned char *)deviationBuf;    //误差图像缓冲区
    rebuildbuffer = (unsigned char *)rebuildBuf;        //重建图像缓冲区

    for (i = 0; i < height; i++)
    {
        for (j = 0; j < width; j++)
        {
            /*256级的灰度图像，预测值范围为[-255,255]，
            8bit量化则除以2，将预测值范围变为[-127,127]，
            再加128后可转到正常灰度显示
            */
            if (j == 0)//对第一个像素进行误差预测
            {
                deviation = (*ybuffer - 128)/2+128;//量化后的预测误差
                *deviationbuffer = (unsigned char)deviation;

                deviation = (*deviationbuffer - 128)*2+128;//反量化后的预测误差
                *rebuildbuffer = (unsigned char)deviation;

                ybuffer++;
                deviationbuffer++;
                rebuildbuffer++;
            }
            else//对其余像素进行误差预测
            {
                deviation = (*ybuffer - *(rebuildbuffer-1))/2+128;//量化后的预测误差
                *deviationbuffer = (unsigned char)deviation;

                deviation = (*deviationbuffer - 128)*2 + *(rebuildbuffer - 1);//反量化后的预测误差
                *rebuildbuffer = (unsigned char)deviation;

                ybuffer++;
                deviationbuffer++;
                rebuildbuffer++;
            }
        }
    }
}

原图像	预测误差图像	重建图像	原图像概率分布	预测误差图像概率分布

压缩性能比较：

文件名称	源文件大小(KB)	huffman变换(KB)	压缩比	DPCM+huffman变换(KB)	压缩比
birds.bmp	384	304	1.26	148	2.59
lena.bmp	64	53	1.20	37	1.73
camman.bmp	64	50	1.28	34	1.88

  预测误差图像都为明显的灰色，电平集中分布在128附近，量化过程中将量化误差抬升128电平所以表明实际预测误差值集中分布在 0 左右，证明对于正常图像，相邻像素之间存在很强的关联性，利用相关性对像素量化后进行压缩压缩比会很理想。