quantize.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 "quantize.h"
#include "mathutil.h"

/****

the intent here is just to stuff the floats to ints, and
get as much extra stuff out of it as possible

we also get rid of signs here : the ints output by quantize
are all positive, with the sign bit in the last bit of the int

BTW one of the things a quantizer could do to perform better would be:
	instead of restoring to the middle of the bucket, restore to the
		average of the values that got put in that bucket.

*****/

void doquantize(void *plane,int width,int height,int stride,float Q)
{
int x,y;
float Qinv;
float *bptr;

	assert(float_DoesRoundToZero());

	Qinv = 1.0f/Q;

	bptr = plane;

	for(y=0;y<height;y++)
	{
	uint sign,qval;
	float val;

		for(x=0;x<width;x++)
		{
			val = *bptr;

			if ( val < 0 )
			{
				sign = 1;
				val = - val;
			}
			else
			{
				sign = 0;
			}

			if ( val < Q )
			{
				*((uint *)bptr) = 0;
			}
			else
			{
				val = (val - Q)*Qinv;
				qval = ftoi(val) + 1;
				*((uint *)bptr) = (qval<<1) + sign;
			}

			bptr++;
		}

		bptr += stride - width;
	}
}

void dequantizerow(uint *fm,float *to,int width,float Q)
{
float val;
uint sign,qval;

	assert(float_DoesRoundToZero());

	// @@ should write 'dequantizerow' in ASM

	while(width--)
	{
		qval = *fm++;
		
		if ( qval == 0 )
		{
			*to++ = 0.0f;
		}
		else
		{
			sign = qval&1;
			qval >>= 1;
			assert( qval );

			// <> goddamned compiler creates an FSTP FLD redundant pair here cuz of the itof inline
			val = (itof(qval) + 0.5f)*Q;

			if ( sign ) val = -val;
			*to++ = val;
		}
	}
}


void dequantize(void * plane,int width,int height,int stride,float Q)
{
float * bptr;
int x,y;

	assert(float_DoesRoundToZero());

	bptr = plane;

	for(y=0;y<height;y++)
	{
	uint sign,qval;
	float val;

		for(x=0;x<width;x++)
		{
			qval = *((uint *)bptr);
			
			if ( qval == 0 )
			{
				*bptr = 0.0f;
			}
			else
			{
				sign = qval&1;
				qval >>= 1;
				assert( qval );

				val = (itof(qval) + 0.5f)*Q;

				if ( sign ) val = -val;
				*bptr = val;
			}
			bptr++;
		}

		bptr += stride - width;
	}
}


void doquantizenopack(void *plane,int width,int height,int stride,float Q)
{
int x,y;
float Qinv;
float *bptr;

	assert(float_DoesRoundToZero());

	Qinv = 1.0f/Q;

	bptr = plane;

	for(y=0;y<height;y++)
	{
	int sign,qval;
	float val;

		for(x=0;x<width;x++)
		{
			val = *bptr;

			if ( val < 0 )
			{
				sign = -1;
				val = - val;
			}
			else
			{
				sign = 1;
			}

			if ( val < Q )
			{
				*((int *)bptr) = 0;
			}
			else
			{
				val = (val - Q)*Qinv;
				qval = ftoi(val) + 1;
				*((int *)bptr) = qval * sign;
			}

			bptr++;
		}

		bptr += stride - width;
	}
}

void dequantizenopack(void * plane,int width,int height,int stride,float Q)
{
float * bptr;
int x,y;

	assert(float_DoesRoundToZero());

	bptr = plane;

	for(y=0;y<height;y++)
	{
	int qval;

		for(x=0;x<width;x++)
		{
			qval = *((int *)bptr);
			
			if ( qval == 0 )
			{
				*bptr = 0.0f;
			}
			else
			{
				if ( qval > 0 )
					*bptr = (itof(qval) + 0.5f)*Q;
				else
					*bptr = - (itof(-qval) + 0.5f)*Q;
			}
			bptr++;
		}

		bptr += stride - width;
	}
}