adapt_quant.c

MPEG-4编解码的实现(包括MPEG4视音频编解码)

#include "../portab.h"
#include "adapt_quant.h"

#include <stdlib.h> /* free, malloc */

#define MAX(a,b)      (((a) > (b)) ? (a) : (b))
#define RDIFF(a,b)    ((int)(a+0.5)-(int)(b+0.5))

int normalize_quantizer_field(float *in, int *out, int num, int min_quant, int max_quant)
{
	int i;
	int finished;
	
	do
	{    
		finished = 1;
		for(i = 1; i < num; i++)
		{
			if(RDIFF(in[i], in[i-1]) > 2)
			{
				in[i] -= (float) 0.5;
				finished = 0;
			}
			else if(RDIFF(in[i], in[i-1]) < -2)
			{
				in[i-1] -= (float) 0.5;
				finished = 0;
			}
        
			if(in[i] > max_quant)
			{
				in[i] = (float) max_quant;
				finished = 0;
			}
			if(in[i] < min_quant)
			{ 
				in[i] = (float) min_quant;
				finished = 0;
			}
			if(in[i-1] > max_quant)
			{ 
				in[i-1] = (float) max_quant;
				finished = 0;
			}
			if(in[i-1] < min_quant) 
			{ 
				in[i-1] = (float) min_quant;
				finished = 0;
			}
		}
	} while(!finished);
	
	out[0] = 0;
	for (i = 1; i < num; i++)
		out[i] = RDIFF(in[i], in[i-1]);
	
	return (int) (in[0] + 0.5);
}

int adaptive_quantization(unsigned char* buf, int stride, int* intquant, 
			  int framequant, int min_quant, int max_quant,
			  int mb_width, int mb_height)  // no qstride because normalization
{
	int i,j,k,l;
	
	static float *quant;
	unsigned char *ptr;
	float *val;
	float global = 0.;
	uint32_t mid_range = 0;

	const float DarkAmpl    = 14 / 2;
	const float BrightAmpl  = 10 / 2;
	const float DarkThres   = 70;
	const float BrightThres = 200;

	const float GlobalDarkThres = 60;
	const float GlobalBrightThres = 170;

	const float MidRangeThres = 20;
	const float UpperLimit = 200;
	const float LowerLimit = 25;

	
	if(!quant)
		if(!(quant = (float *) malloc(mb_width*mb_height * sizeof(float))))
			return -1;

	val = (float *) malloc(mb_width*mb_height * sizeof(float));

	for(k = 0; k < mb_height; k++)
	{
		for(l = 0;l < mb_width; l++)        // do this for all macroblocks individually 
		{
			quant[k*mb_width+l] = (float) framequant;
			
			// calculate luminance-masking
			ptr = &buf[16*k*stride+16*l];			// address of MB
			
			val[k*mb_width+l] = 0.;
			
			for(i = 0; i < 16; i++)
				for(j = 0; j < 16; j++)
					val[k*mb_width+l] += ptr[i*stride+j];
			val[k*mb_width+l] /= 256.;
			global += val[k*mb_width+l];

			if((val[k*mb_width+l] > LowerLimit) && (val[k*mb_width+l] < UpperLimit))
				mid_range++;
		}
	}

	global /= mb_width*mb_height;

	if(((global < GlobalBrightThres) && (global > GlobalDarkThres))
	   || (mid_range < MidRangeThres)) {
		for(k = 0; k < mb_height; k++)
		{
			for(l = 0;l < mb_width; l++)        // do this for all macroblocks individually 
			{
				if(val[k*mb_width+l] < DarkThres)
					quant[k*mb_width+l] += DarkAmpl*(DarkThres-val[k*mb_width+l])/DarkThres;
				else if (val[k*mb_width+l]>BrightThres)
					quant[k*mb_width+l] += BrightAmpl*(val[k*mb_width+l]-BrightThres)/(255-BrightThres);
			}
		}
	}
	free(val);
	return normalize_quantizer_field(quant, intquant, mb_width*mb_height, min_quant, max_quant);
}