实验四——DPCM编码（1bit、2bit、4bit、8bit量化）
一.实验要求
本实验的目标是验证DPCM编码的编码效率。首先读取一个256级的灰度图像，采用自己设定的预测方法计算预测误差（本次实验报告使用左向预测），并对预测误差进行8比特均匀量化（基本要求）。还可对预测误差进行1比特、2比特和4比特的量化设计（提高要求）。
在DPCM编码器实现的过程中可同时输出预测误差图像和重建图像。将预测误差图像写入文件并将该文件输入Huffman编码器，得到输出码流、给出概率分布图并计算压缩比。将原始图像文件输入Huffman编码器，得到输出码流、给出概率分布图并计算压缩比。最后比较两种系统（1.DPCM+熵编码和2.仅进行熵编码）之间的编码效率（压缩比和图像质量）。压缩质量以PSNR进行计算。
二.实验原理
8bit量化：由于原始Y图像的像素的Y值的取值范围为0～255，故预测误差Pn的取值范围为-255～255，要将其量化限制在0～255的范围内。对于8bit量化，将Pn除2可将Pn的范围变成-128～127（实验中Pn使用int型存储，int型自动取整故范围变为-128～127），再整体加上128则范围变成0～255，刚好可以用8bit表示。故将unsigned char（Pn/2+128）存储到误差图像的当前样本值中。特别注意：原始Y图像每行第一个值直接存储到误差图像和存储器中的图像上，误差图像中每行第一个必须为原始Y图像的每行第一个值而不能为0，否则恢复时没有第一个元素值不能恢复。
4bit量化：4bit量化的难点在于：1）误差图像中存储的每个像素对应4bit，非整数字节，存在非整数字节存取问题，本次实验中使用的解决方法是定义位域结构体。注意每行第一个的误差值仍使用8bit来表示2）4bit表示范围为0000～1111，每个码字的值并不与预测误差的值相等，需要设计规则将-255～255、0000～1111、0～255三者对应起来。解决方法：-255～255转化为0000～1111的方法：对于-255～255区间，处于区间下半段的值令其量化后首位为0，处于上半段的令其量化后首位为1，再在小区间中用此方法，以此类推，伪代码如下：
for(i=0;i<4;i++)
{
if(Pn>(max+min)/2)
{
当位为1；
min=(max+min)/2;
}
else
{
当位为0；
max=(max+min)/2;
}
}
三.关键代码及分析
1.缓冲区分配
2.当位置1置0的实现
error_buffer_4bit->data=0;
switch(k)
{
case 0:error_buffer_4bit->data|=0x8; break;
case 1:error_buffer_4bit->data|=0x4; break;
case 2:error_buffer_4bit->data|=0x2; break;
case 3:error_buffer_4bit->data|=0x1; break;
}先将当前样本误差值置0，则四位均初始化为0，置0时不需要再操作，只需要编写置1的代码。k为0的时候要将首位置1，故将其与1000（0x8）按位或来实现，其余三位同理。
四.完整代码
1.8bit量化
#include
#include
int main(int argc, char** argv)
{
int height,width;
char *filename_yuv,*filename_error,*filename_decoding;
filename_yuv=argv[1];
height=atoi(argv[2]);
width=atoi(argv[3]);
filename_error=argv[4];
filename_decoding=argv[5];
unsigned char *YUV_buffer=NULL,*Y_buffer;
unsigned char *YUV_buffer_del;
YUV_buffer=new unsigned char[height*width*3/2];
YUV_buffer_del=YUV_buffer;
if((width%2==1)||(height%2==1))
{
printf("please input the right height and width/n");
}
FILE *fp_yuv=NULL,*fp_error=NULL,*fp_decoding=NULL;
fp_yuv=fopen(filename_yuv,"rb");
fp_error=fopen(filename_error,"wb");
fp_decoding=fopen(filename_decoding,"wb");
if((fp_yuv==NULL)||(fp_error==NULL)||(fp_decoding==NULL))
{
printf("can not open the file/n");
exit(1);
}
fread(YUV_buffer,sizeof(unsigned char),height*width*3/2,fp_yuv);
Y_buffer=YUV_buffer;
unsigned char *error_buffer,*decoding_buffer;
error_buffer=new unsigned char[height*width*3/2];
decoding_buffer=new unsigned char[height*width*3/2];
unsigned char *Y_buffer_operate,*error_buffer_operate,*decoding_buffer_operate;
unsigned char *Y_buffer_del,*error_buffer_del,*decoding_buffer_del;
Y_buffer_del=Y_buffer;
error_buffer_del=error_buffer;
decoding_buffer_del=decoding_buffer;
Y_buffer_operate=Y_buffer;
error_buffer_operate=error_buffer;
decoding_buffer_operate=decoding_buffer;
for(int i=0;i 2.4bit量化
#include
#include
typedef struct definedtype
{
unsigned char data:4;//定义4bit类型
}Bit4;
int main(int argc, char** argv)
{
int height,width;
char *filename_yuv,*filename_error,*filename_decoding;
filename_yuv=argv[1];
height=atoi(argv[2]);
width=atoi(argv[3]);
filename_error=argv[4];
filename_decoding=argv[5];
unsigned char *YUV_buffer=NULL,*Y_buffer;
unsigned char *YUV_buffer_del;
YUV_buffer=new unsigned char[height*width*3/2];
YUV_buffer_del=YUV_buffer;
if((width%2==1)||(height%2==1))
{
printf("please input the right height and width/n");
}
FILE *fp_yuv=NULL,*fp_error=NULL,*fp_decoding=NULL;
fp_yuv=fopen(filename_yuv,"rb");
fp_error=fopen(filename_error,"wb");
fp_decoding=fopen(filename_decoding,"wb");
if((fp_yuv==NULL)||(fp_error==NULL)||(fp_decoding==NULL))
{
printf("can not open the file/n");
exit(1);
}
fread(YUV_buffer,sizeof(unsigned char),height*width*3/2,fp_yuv);
Y_buffer=YUV_buffer;
unsigned char *error_buffer,*decoding_buffer;
error_buffer=new unsigned char[height*width*3/2];
decoding_buffer=new unsigned char[height*width*3/2];
unsigned char *Y_buffer_operate,*error_buffer_operate,*decoding_buffer_operate;
unsigned char *Y_buffer_del,*error_buffer_del,*decoding_buffer_del;
Y_buffer_del=Y_buffer;
error_buffer_del=error_buffer;
decoding_buffer_del=decoding_buffer;
Y_buffer_operate=Y_buffer;
error_buffer_operate=error_buffer;
decoding_buffer_operate=decoding_buffer;
//定义用来存储4bit量化的预测误差
Bit4 *error_buffer_4bit,*error_buffer_4bit_del;
error_buffer_4bit=new Bit4[height*width+height];
error_buffer_4bit_del=error_buffer_4bit;
for(int i=0;idata=0;
for(int k=0;k<4;k++)
{
if(temp_pn>(max+min)/2)
{
switch(k)
{
case 0:error_buffer_4bit->data|=0x8; break;
case 1:error_buffer_4bit->data|=0x4; break;
case 2:error_buffer_4bit->data|=0x2; break;
case 3:error_buffer_4bit->data|=0x1; break;
}
min=(max+min)/2;
}
else
{
max=(max+min)/2;
}
}
//4bit转化为[0~255]可输出的存储到error_buffer_operate
*error_buffer_operate=16*((*error_buffer_4bit).data);
//反量化
*decoding_buffer_operate=16*((*error_buffer_4bit).data)-128+temp_last_xn;
Y_buffer_operate++;
error_buffer_4bit++;
error_buffer_operate++;
decoding_buffer_operate++;
}
}
}
for(int i=0;i 3.2bit量化
#include
#include
typedef struct definedtype
{
unsigned char data:2;//定义2bit类型
}Bit2;
int main(int argc, char** argv)
{
int height,width;
char *filename_yuv,*filename_error,*filename_decoding;
filename_yuv=argv[1];
height=atoi(argv[2]);
width=atoi(argv[3]);
filename_error=argv[4];
filename_decoding=argv[5];
unsigned char *YUV_buffer=NULL,*Y_buffer;
unsigned char *YUV_buffer_del;
YUV_buffer=new unsigned char[height*width*3/2];
YUV_buffer_del=YUV_buffer;
if((width%2==1)||(height%2==1))
{
printf("please input the right height and width/n");
}
FILE *fp_yuv=NULL,*fp_error=NULL,*fp_decoding=NULL;
fp_yuv=fopen(filename_yuv,"rb");
fp_error=fopen(filename_error,"wb");
fp_decoding=fopen(filename_decoding,"wb");
if((fp_yuv==NULL)||(fp_error==NULL)||(fp_decoding==NULL))
{
printf("can not open the file/n");
exit(1);
}
fread(YUV_buffer,sizeof(unsigned char),height*width*3/2,fp_yuv);
Y_buffer=YUV_buffer;
unsigned char *error_buffer,*decoding_buffer;
error_buffer=new unsigned char[height*width*3/2];
decoding_buffer=new unsigned char[height*width*3/2];
unsigned char *Y_buffer_operate,*error_buffer_operate,*decoding_buffer_operate;
unsigned char *Y_buffer_del,*error_buffer_del,*decoding_buffer_del;
Y_buffer_del=Y_buffer;
error_buffer_del=error_buffer;
decoding_buffer_del=decoding_buffer;
Y_buffer_operate=Y_buffer;
error_buffer_operate=error_buffer;
decoding_buffer_operate=decoding_buffer;
//定义用来存储2bit量化的预测误差
Bit2 *error_buffer_2bit,*error_buffer_2bit_del;
error_buffer_2bit=new Bit2[height*width+height*3];
error_buffer_2bit_del=error_buffer_2bit;
for(int i=0;idata=0;
for(int k=0;k<2;k++)
{
if(temp_pn>(max+min)/2)
{
switch(k)
{
case 0:error_buffer_2bit->data|=0x2; break;
case 1:error_buffer_2bit->data|=0x1; break;
}
min=(max+min)/2;
}
else
{
max=(max+min)/2;
}
}
//4bit转化为[0~255]可输出的存储到error_buffer_operate
*error_buffer_operate=64*((*error_buffer_2bit).data);
//反量化
*decoding_buffer_operate=64*((*error_buffer_2bit).data)-128+temp_last_xn;
Y_buffer_operate++;
error_buffer_2bit++;
error_buffer_operate++;
decoding_buffer_operate++;
}
}
}
for(int i=0;i 4.1bit量化
#include
#include
typedef struct definedtype
{
unsigned char data:1;//定义2bit类型
}Bit1;
int main(int argc, char** argv)
{
int height,width;
char *filename_yuv,*filename_error,*filename_decoding;
filename_yuv=argv[1];
height=atoi(argv[2]);
width=atoi(argv[3]);
filename_error=argv[4];
filename_decoding=argv[5];
unsigned char *YUV_buffer=NULL,*Y_buffer;
unsigned char *YUV_buffer_del;
YUV_buffer=new unsigned char[height*width*3/2];
YUV_buffer_del=YUV_buffer;
if((width%2==1)||(height%2==1))
{
printf("please input the right height and width/n");
}
FILE *fp_yuv=NULL,*fp_error=NULL,*fp_decoding=NULL;
fp_yuv=fopen(filename_yuv,"rb");
fp_error=fopen(filename_error,"wb");
fp_decoding=fopen(filename_decoding,"wb");
if((fp_yuv==NULL)||(fp_error==NULL)||(fp_decoding==NULL))
{
printf("can not open the file/n");
exit(1);
}
fread(YUV_buffer,sizeof(unsigned char),height*width*3/2,fp_yuv);
Y_buffer=YUV_buffer;
unsigned char *error_buffer,*decoding_buffer;
error_buffer=new unsigned char[height*width*3/2];
decoding_buffer=new unsigned char[height*width*3/2];
unsigned char *Y_buffer_operate,*error_buffer_operate,*decoding_buffer_operate;
unsigned char *Y_buffer_del,*error_buffer_del,*decoding_buffer_del;
Y_buffer_del=Y_buffer;
error_buffer_del=error_buffer;
decoding_buffer_del=decoding_buffer;
Y_buffer_operate=Y_buffer;
error_buffer_operate=error_buffer;
decoding_buffer_operate=decoding_buffer;
//定义用来存储2bit量化的预测误差
Bit1 *error_buffer_1bit,*error_buffer_1bit_del;
error_buffer_1bit=new Bit1[height*width+height*7];
error_buffer_1bit_del=error_buffer_1bit;
for(int i=0;idata=0;
if(temp_pn>(max+min)/2)
{
error_buffer_1bit->data|=0x1;
min=(max+min)/2;
}
else
{
max=(max+min)/2;
}
//1bit转化为[0~255]可输出的存储到error_buffer_operate
*error_buffer_operate=128*((*error_buffer_1bit).data);
//反量化
*decoding_buffer_operate=128*((*error_buffer_1bit).data)-128+temp_last_xn;
Y_buffer_operate++;
error_buffer_1bit++;
error_buffer_operate++;
decoding_buffer_operate++;
}
}
}
for(int i=0;i 四.实验结果
1.湖面倒影图：
8bit：
4bit：
2bit：
1bit：
2.Lena图：
8bit：
4bit：
2bit：
1bit：
3.湖面倒影图的haffcode比较：
4.湖面倒影图的PSNR值：
8bit、4bit恢复图像相对于原始图像的psnr