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src/Source/FreeImage/tmoColorConvert.cpp  view on Meta::CPAN

	float max_lum = -1e20F, min_lum = 1e20F;
	double sumLum = 0, sumLogLum = 0;

	BYTE *bits = (BYTE*)FreeImage_GetBits(dib);
	for(unsigned y = 0; y < height; y++) {
		const float *pixel = (float*)bits;
		for(unsigned x = 0; x < width; x++) {
			const float Y = pixel[x];
			max_lum = (max_lum < Y) ? Y : max_lum;				// max Luminance in the scene
			min_lum = ((Y > 0) && (min_lum < Y)) ? min_lum : Y;	// min Luminance in the scene
			sumLum += Y;										// average luminance
			sumLogLum += log(2.3e-5F + Y);						// contrast constant in Tumblin paper
		}
		// next line
		bits += pitch;
	}

	// maximum luminance
	*maxLum = max_lum;
	// minimum luminance
	*minLum = min_lum;
	// average luminance
	*Lav = (float)(sumLum / (width * height));
	// average log luminance, a.k.a. world adaptation luminance
	*Llav = (float)exp(sumLogLum / (width * height));

	return TRUE;
}
// --------------------------------------------------------------------------

static void findMaxMinPercentile(FIBITMAP *Y, float minPrct, float *minLum, float maxPrct, float *maxLum) {
	int x, y;
	int width = FreeImage_GetWidth(Y);
	int height = FreeImage_GetHeight(Y);
	int pitch = FreeImage_GetPitch(Y);

	std::vector<float> vY(width * height);

	BYTE *bits = (BYTE*)FreeImage_GetBits(Y);
	for(y = 0; y < height; y++) {
		float *pixel = (float*)bits;
		for(x = 0; x < width; x++) {
			if(pixel[x] != 0) {
				vY.push_back(pixel[x]);
			}
		}
		bits += pitch;
	}

	std::sort(vY.begin(), vY.end());
	
	*minLum = vY.at( int(minPrct * vY.size()) );
	*maxLum = vY.at( int(maxPrct * vY.size()) );
}

/**
Clipping function<br>
Remove any extremely bright and/or extremely dark pixels 
and normalize between 0 and 1. 
@param Y Input/Output image
@param minPrct Minimum percentile
@param maxPrct Maximum percentile
*/
void 
NormalizeY(FIBITMAP *Y, float minPrct, float maxPrct) {
	int x, y;
	float maxLum, minLum;

	if(minPrct > maxPrct) {
		// swap values
		float t = minPrct; minPrct = maxPrct; maxPrct = t;
	}
	if(minPrct < 0) minPrct = 0;
	if(maxPrct > 1) maxPrct = 1;

	int width = FreeImage_GetWidth(Y);
	int height = FreeImage_GetHeight(Y);
	int pitch = FreeImage_GetPitch(Y);

	// find max & min luminance values
	if((minPrct > 0) || (maxPrct < 1)) {
		maxLum = 0, minLum = 0;
		findMaxMinPercentile(Y, minPrct, &minLum, maxPrct, &maxLum);
	} else {
		maxLum = -1e20F, minLum = 1e20F;
		BYTE *bits = (BYTE*)FreeImage_GetBits(Y);
		for(y = 0; y < height; y++) {
			const float *pixel = (float*)bits;
			for(x = 0; x < width; x++) {
				const float value = pixel[x];
				maxLum = (maxLum < value) ? value : maxLum;	// max Luminance in the scene
				minLum = (minLum < value) ? minLum : value;	// min Luminance in the scene
			}
			// next line
			bits += pitch;
		}
	}
	if(maxLum == minLum) return;

	// normalize to range 0..1 
	const float divider = maxLum - minLum;
	BYTE *bits = (BYTE*)FreeImage_GetBits(Y);
	for(y = 0; y < height; y++) {
		float *pixel = (float*)bits;
		for(x = 0; x < width; x++) {
			pixel[x] = (pixel[x] - minLum) / divider;
			if(pixel[x] <= 0) pixel[x] = EPSILON;
			if(pixel[x] > 1) pixel[x] = 1;
		}
		// next line
		bits += pitch;
	}
}