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Author: mcychan

nQuantCpp/DblGNGQuantizer.cpp

@@ -633,8 +633,6 @@ namespace GrowingNeuralGas
 			}
 		}
 
-		if (mDivn < .04 && PG < 1 && PG >= coeffs[0][1] && nMaxColors >= 64)
-			enforcedDither = false;
 		if (mDivn > .0029 && nMaxColors <= 32)
 			enforcedDither = false;
 
@@ -669,7 +667,7 @@ namespace GrowingNeuralGas
 					return nearestColorIndex(pPalette, nMaxColors, argb, pos);
 				return closestColorIndex(pPalette, nMaxColors, argb, pos);
 			};
-			return dither_image(pixels.data(), pPalette, nMaxColors, NearestColorIndex, hasSemiTransparency, m_transparentPixelIndex, qPixels, width, height);
+			return dither_image(pixels.data(), pPalette, nMaxColors, NearestColorIndex, hasSemiTransparency, m_transparentPixelIndex, qPixels, width, height, saliencies, enforcedDither);
 		}
 
 		UINT pixelIndex = 0;
@@ -685,16 +683,6 @@ namespace GrowingNeuralGas
 	{
 		const auto bitmapHeight = pixels.size() / bitmapWidth;
 
-		if (dither && !enforcedDither) {
-			auto qPixels = make_unique<unsigned short[]>(pixels.size());
-			quantize_image(pixels, pPalette, nMaxColors, qPixels.get(), bitmapWidth, bitmapHeight, dither);
-
-			pixelMap.clear();
-			clear();
-
-			return ProcessImagePixels(pDest, qPixels.get(), m_transparentPixelIndex >= 0);
-		}
-
 		if (dither) {
 			saliencies.resize(pixels.size());
 			auto saliencyBase = .1f;
@@ -712,6 +700,17 @@ namespace GrowingNeuralGas
 		if (enforcedDither)
 			enforcedDither = nMaxColors < 32 || nMaxColors > 64;
 
+		bool sortedByYDiff = nMaxColors >= 128 && mDivn >= .02 && (!hasAlpha() || mDivn < .18);
+		if (dither && (sortedByYDiff || !enforcedDither)) {
+			auto qPixels = make_unique<unsigned short[]>(pixels.size());
+			quantize_image(pixels, pPalette, nMaxColors, qPixels.get(), bitmapWidth, bitmapHeight, dither);
+
+			pixelMap.clear();
+			clear();
+
+			return ProcessImagePixels(pDest, qPixels.get(), m_transparentPixelIndex >= 0);
+		}		
+
 		auto GetColorIndex = [&](const Color& c) -> int {
 			return GetARGBIndex(c, hasSemiTransparency, hasAlpha());
 		};

nQuantCpp/bitmapUtilities.cpp

@@ -4,6 +4,7 @@
 // GetBitmapHeaderSize
 //
 #include "bitmapUtilities.h"
+#include <algorithm>
 
 ULONG GetBitmapHeaderSize(LPCVOID pDib)
 {
@@ -663,6 +664,55 @@ bool dithering_image(const ARGB* pixels, const ColorPalette* pPalette, DitherFn
 	return true;
 }
 
+// Standard Interleaved Gradient Noise formula by Jorge Jimenez
+inline float GetInterleavedGradientNoise(int x, int y)
+{
+	// Returns a pseudo-random value between 0.0f and 1.0f
+	return fmod(52.9829189f * fmod(0.06711056f * float(x) + 0.00583715f * float(y), 1.0f), 1.0f);
+}
+
+bool dither_image(const ARGB* pixels, const ARGB* pPalette, const UINT nMaxColors, DitherFn ditherFn,
+	const bool& hasSemiTransparency, const int& transparentPixelIndex, unsigned short* qPixels,
+	const UINT width, const UINT height, const vector<float>& saliencies, bool enforcedDither)
+{
+	// Base spread determined by palette density
+	const float baseSpread = 255.0f / cbrt(static_cast<float>(nMaxColors));
+
+	for (UINT y = 0; y < height; ++y)
+	{
+		for (UINT x = 0; x < width; ++x)
+		{
+			UINT pixelIndex = y * width + x;
+			Color c(pixels[pixelIndex]);
+
+			// Handle pure transparency early
+			if (transparentPixelIndex >= 0 && c.GetA() == 0) {
+				qPixels[pixelIndex] = static_cast<unsigned short>(transparentPixelIndex);
+				continue;
+			}
+
+			// Generate centered noise [-0.5, 0.5]
+			float noise = GetInterleavedGradientNoise(static_cast<int>(x), static_cast<int>(y)) - 0.5f;
+
+			// Compute noise offset. If saliencies, modulate by pixel saliency;
+			// otherwise, use uniform base noise intensity across the image.
+			float weight = enforcedDither && !saliencies.empty() ? saliencies[pixelIndex] : 1.0f;
+			float offset = noise * baseSpread * weight;
+
+			// Apply noise and clamp safely to RGB limits
+			int r = clamp(static_cast<int>(c.GetR() + offset), 0, 255);
+			int g = clamp(static_cast<int>(c.GetG() + offset), 0, 255);
+			int b = clamp(static_cast<int>(c.GetB() + offset), 0, 255);
+			int a = c.GetA();
+
+			auto noisyArgb = Color::MakeARGB(a, r, g, b);
+			qPixels[pixelIndex] = ditherFn(pPalette, nMaxColors, noisyArgb, y + x);
+		}
+	}
+
+	return true;
+}
+
 bool ProcessImagePixels(Bitmap* pDest, const ARGB* qPixels, const bool& hasSemiTransparency, const int& transparentPixelIndex)
 {
 	UINT bpp = GetPixelFormatSize(pDest->GetPixelFormat());

nQuantCpp/bitmapUtilities.h

@@ -76,6 +76,10 @@ bool dither_image(const ARGB* pixels, const ARGB* pPalette, const UINT nMaxColor
 
 bool dithering_image(const ARGB* pixels, const ColorPalette* pPalette, DitherFn ditherFn, const bool& hasSemiTransparency, const int& transparentPixelIndex, const UINT nMaxColors, ARGB* qPixels, const UINT width, const UINT height);
 
+bool dither_image(const ARGB* pixels, const ARGB* pPalette, const UINT nMaxColors, DitherFn ditherFn,
+	const bool& hasSemiTransparency, const int& transparentPixelIndex, unsigned short* qPixels,
+	const UINT width, const UINT height, const vector<float>& saliencies, bool enforcedDither);
+
 bool ProcessImagePixels(Bitmap* pDest, const ARGB* qPixels, const bool& hasSemiTransparency, const int& transparentPixelIndex);
 
 bool ProcessImagePixels(Bitmap* pDest, const unsigned short* qPixels, const bool hasTransparent);