trans_cdf22.c

傅立叶变换和小波变换是图像压缩的重要工具。该代大戏是利用小波变换进行图像压缩。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <crblib/inc.h>
#include "transform.h"

// @@ can I do better rounding here, like a (+1) in each * 0.5f ?

void forwardCDF22(float *data,float *low,float *high,int half)
{
int x;
float *ptr;

	assert( half >= 2 );

	ptr = data;

	*high = ptr[1] - ((ptr[2] + ptr[0]) * 0.5f);
	*low  = ptr[0] + (high[0] * 0.5f);
	ptr += 2; high++; low++;

	for(x=(half-2);x--;)
	{
		*high = ptr[1] - ((ptr[2] + ptr[0]) * 0.5f);
		*low =  ptr[0] + ((high[0] + high[-1])*0.25f);

		/*
		p0 + 1/4*(p1 - (p0 +p2)/2 + p-1 - (p0 + p-2)/2 )
		1/4 * [ 3 * p0 + p1 + p-1 - (p2 + p-2)/2 ) ]
		*/

		ptr += 2;
		high++; low++;
	}

	*high = ptr[1] - ptr[0];
	*low = *ptr + ((high[0] + high[-1])*0.25f);
}

void inverseCDF22(float *data,float *low,float *high,int half)
{
float *ptr;
int x;

	ptr = data;
	
	ptr[0] = low[0] - ((high[0])*0.5f);
	ptr += 2; high++; low++;
	
	for(x=(half-1);x--;)
	{
		ptr[ 0] = low[0]  - ((high[0] + high[-1])*0.25f);
		ptr[-1] = high[-1] + ((ptr[0] + ptr[-2])*0.5f);
		ptr += 2; high++; low++;
	}

	ptr[-1] = high[-1] + ptr[-2];
}

void inverseCDF22rows(RowAbstract *out,RowBuffer * lowTB,RowBuffer * highTB,int y)
{
float *low0,*high0,*high1;
int x,width;

	width = out->width;
	low0  = RowBuffer_Row(lowTB,0);
	high0 = RowBuffer_Row(highTB,0);
	high1 = RowBuffer_Row(highTB,-1);

	// we normally write two rows out;
	//	the first time we can only do one, the last time we can do three

	// 3dnow : PAVGUSB does 8 ubyte averages: A = (B+C+1)>>1 !!!
	// katmai-mmx has one too;
	// however, we can't get the wavelet coefficients in bytes;
	//	is there a PAVGW ?

	if ( y == 0 ) // first one
	{
	float *out0;
		out0 = RowAbstract_Row(out,0);
		for(x=width;x--;)
		{
			*out0++ = (*low0++) - ((*high0++)*0.5f);
		}
		RowAbstract_Advance(out,1);
	}
	else if ( y == (out->halfh-1) ) // last one
	{
	float *out0,*out1,*outP,*out2;
		outP = RowAbstract_Row(out,-1);
		out0 = RowAbstract_Row(out,0);
		out1 = RowAbstract_Row(out,1);
		out2 = RowAbstract_Row(out,2);
		for(x=width;x--;)
		{
			*out1 = *low0  - ((*high0 + *high1)*0.25f);
			*out0 = *high1 + ((*out1  + *outP )*0.5f );
			*out2 = *high0 + *out1;

			low0++; high0++; high1++;
			out0++; out1++; out2++; outP++;
		}
		RowAbstract_Advance(out,3);
	}
	else
	{
	float *out0,*out1,*outP;
		outP = RowAbstract_Row(out,-1);
		out0 = RowAbstract_Row(out,0);
		out1 = RowAbstract_Row(out,1);
		for(x=width;x--;)
		{
			*out1 = *low0  - ((*high0 + *high1)*0.25f);
			*out0 = *high1 + ((*out1  + *outP )*0.5f);
			low0++; high0++; high1++;
			out0++; out1++; outP++;
		}
		RowAbstract_Advance(out,2);
	}
}

Transform transformCDF22 =
{
	forwardCDF22,
	inverseCDF22,
	"CDF22",
	1,2,
	inverseCDF22rows
};