DPCM预测编码

DPCM编码原理框图

编码器

               

解码器

实现算法

在原来的BMP2YUV的基础上面，加一个DPCM过程的函数（只考虑了Y亮度值）

这个是8bit量化采用的算法

8bit实验结果：

原图	误差	重建

四比特的时候

#include "stdlib.h"
#include 
#include 
#include "rgb2yuv.h" 
#include 
#include 
void out_Buffer(unsigned char *ybuf, unsigned char *rebuf, unsigned char *ebuf, BITMAPFILEHEADER &file_h, BITMAPINFOHEADER & info_h)
{
	unsigned long  pix_h, pix_w;
	int count=0;
	int lev = 5;
	int div = pow((double)2,9-lev);
	int lev_8 = 128;
	int lev_2 = 255;
	pix_h = info_h.biHeight;
	if (info_h.biWidth *info_h.biBitCount % 32 == 0)
	{
		pix_w = info_h.biWidth;
	}
	else
	{
		pix_w = (info_h.biWidth*info_h.biBitCount + 31) / 32 * (32 / info_h.biBitCount);
	}
	for (int i = 0; i < pix_h; i++)
	{

		for (int j = 0; j < pix_w; j++)
		{
			if (count == i * pix_w)
			{
				ebuf[count] = (ybuf[count] - 128) / div + lev_8;
				rebuf[count] = (ebuf[count] - lev_8)*div + 128;
				if (rebuf[count]>255) rebuf[count] = 255;
				if (rebuf[count] < 0) rebuf[count] = 0;
				
			}
			else
			{
				ebuf[count] = (ybuf[count] - rebuf[count - 1] ) /div+ lev_8 ;
				rebuf[count] = (ebuf[count] - lev_8) * div + rebuf[count - 1];
				if (rebuf[count]>255) rebuf[count] = 255;
				if (rebuf[count] < 0) rebuf[count] = 0;

			}
			count = pix_w * i+ j + 1;
		}
	}

抽选三幅

结果如下：

原图	w误差	c重建

2比特的

void out_Buffer(unsigned char *ybuf, unsigned char *rebuf, unsigned char *ebuf, BITMAPFILEHEADER &file_h, BITMAPINFOHEADER & info_h)
{
	unsigned long  pix_h, pix_w;
	int count = 0;
	int lev = 3;
	int div = pow((double)2, 9 - lev);
	int lev_8 = 128;
	int lev_2 = 255;
	int m,n,k,l;
	pix_h = info_h.biHeight;
	if (info_h.biWidth *info_h.biBitCount % 32 == 0)
	{
		pix_w = info_h.biWidth;
	}
	else
	{
		pix_w = (info_h.biWidth*info_h.biBitCount + 31) / 32 * (32 / info_h.biBitCount);
	}
	for (int i = 0; i < pix_h; i++)
	{

		for (int j = 0; j < pix_w; j++)
		{
			if (count == i * pix_w)
			{
				ebuf[count] = (ybuf[count] - 128 ) / div + 128;
				m = ybuf[count] - 128;
				n = (m + 255) / div;
				rebuf[count] =( n-255/div)*div+128;
				
			}
			else
			{
				ebuf[count] = (ybuf[count] - rebuf[count - 1] ) / div + 128;
				m = ybuf[count] - rebuf[count - 1];
				n = (m + 255) / div;
				rebuf[count] = (n - 255 / div)*div + rebuf[count - 1];
				
			
			}
			count = pix_w * i + j + 1;
		}
	}

}

实验结果如下：

原图	误差	重建

1比特的

void out_Buffer(unsigned char *ybuf, unsigned char *rebuf, unsigned char *ebuf, BITMAPFILEHEADER &file_h, BITMAPINFOHEADER & info_h)
{
	unsigned long  pix_h, pix_w;
	int count=0;
	int lev = 2;
	int div = pow((double)2,9-lev);
	int lev_8 = 128;
	int lev_2 = 255;
	pix_h = info_h.biHeight;
	if (info_h.biWidth *info_h.biBitCount % 32 == 0)
	{
		pix_w = info_h.biWidth;
	}
	else
	{
		pix_w = (info_h.biWidth*info_h.biBitCount + 31) / 32 * (32 / info_h.biBitCount);
	}
	for (int i = 0; i < pix_h; i++)
	{

		for (int j = 0; j < pix_w; j++)
		{
			if (count == i * pix_w)
			{
				ebuf[count] = (ybuf[count] - 128+ lev_2) / div +128;

				rebuf[count] = (ebuf[count] - 128)*div + 128;
				if (rebuf[count]>255) rebuf[count] = 255;
				if (rebuf[count] < 0) rebuf[count] = 0;
				
			}
			else
			{
				ebuf[count] = (ybuf[count] - rebuf[count - 1] + lev_2) /div+ 128 ;
				rebuf[count] = (ebuf[count] - 128) * div + rebuf[count - 1];
				if (rebuf[count]>255) rebuf[count] = 255;
				if (rebuf[count] < 0) rebuf[count] = 0;

			}
			count = pix_w * i+ j + 1;
		}
	}

}

抽选3幅结果如下：

原图	误差	重建

实验结果的PSNR值

Huffman编码结果

举8比特的Lena例子,原yuv文件和DPCM编码如下：

原yuv huffman编码：

DPCM编码后的Huffman编码结果：

可以看出来，平均码长和熵的大小在经过DPCM编码重建之后都变小了，但是原始图像的损失人眼辨别不出来，则码率减小，实现了压缩的目的