Index: source/blender/compositor/operations/COM_DilateErodeOperation.cpp
===================================================================
--- source/blender/compositor/operations/COM_DilateErodeOperation.cpp	(revision 49166)
+++ source/blender/compositor/operations/COM_DilateErodeOperation.cpp	(working copy)
@@ -334,39 +334,75 @@
 	if (this->m_cached_buffer == NULL) {
 		MemoryBuffer *buffer = (MemoryBuffer *)this->m_inputProgram->initializeTileData(NULL);
 		float *rectf = buffer->convertToValueBuffer();
-		int x, y, i;
+		int x, y;
 		float *p;
 		int bwidth = buffer->getWidth();
 		int bheight = buffer->getHeight();
-		for (i = 0; i < this->m_iterations; i++) {
+		int bsize = MAX2(bwidth, bheight);
+		int distance = this->m_iterations;
+		if (distance != 0) {
+			// maxleft[i] := maximum of p[i - i%distance] ... p[i], inclusively
+			float *maxleft = new float[bsize];
+			// maxright[i] := maximum of p[i] ... p[i - i%distance + distance - 1], inclusively
+			// That means, maxright[i - i%distance] := maximum of the whole distance-wide block
+			float *maxright = new float[bsize]; 
+			float v;
+			
 			for (y = 0; y < bheight; y++) {
-				for (x = 0; x < bwidth - 1; x++) {
-					p = rectf + (bwidth * y + x);
-					*p = MAX2(*p, *(p + 1));
+				p = rectf + bwidth * y;
+				maxleft[0] = maxright[0] = p[0];
+				for (x = 1; x < bwidth; x++) {
+					v = p[x];
+					maxright[x] = v;
+					if (x % distance && maxleft[x-1] > v)
+						maxleft[x] = maxleft[x-1];
+					else
+						maxleft[x] = v;
 				}
-			}
-		
-			for (y = 0; y < bheight; y++) {
-				for (x = bwidth - 1; x >= 1; x--) {
-					p = rectf + (bwidth * y + x);
-					*p = MAX2(*p, *(p - 1));
+				
+				for (x = bwidth-2; x >= 0; x--) {
+					if ((x+1) % distance && maxright[x+1] > maxright[x])
+						maxright[x] = maxright[x+1];
 				}
+				
+				// Get the actual maximum as maximum of the current distance-wide block and adequate parts of the neighbors
+				for (x = 0; x < distance; x++)
+					p[x] = MAX2(maxright[0], maxleft[x+distance]);
+				for (; x < bwidth-distance; x++)
+					p[x] = MAX3(maxright[x - x%distance], maxright[x-distance], maxleft[x+distance]);
+				for (; x < bwidth; x++)
+					p[x] = MAX2(maxright[x - x%distance], maxright[x-distance]);
 			}
-		
+			
+			// Process all columns in the same manner
 			for (x = 0; x < bwidth; x++) {
-				for (y = 0; y < bheight - 1; y++) {
-					p = rectf + (bwidth * y + x);
-					*p = MAX2(*p, *(p + bwidth));
+				p = rectf + x;
+				maxleft[0] = maxright[0] = p[0];
+				for (y = 1; y < bheight; y++) {
+					v = p[y*bwidth];
+					maxright[y] = v;
+					if (y % distance && maxleft[y-1] > v)
+						maxleft[y] = maxleft[y-1];
+					else
+						maxleft[y] = v;
 				}
-			}
-		
-			for (x = 0; x < bwidth; x++) {
-				for (y = bheight - 1; y >= 1; y--) {
-					p = rectf + (bwidth * y + x);
-					*p = MAX2(*p, *(p - bwidth));
+				
+				for (y = bheight-2; y >= 0; y--) {
+					if ((y+1) % distance && maxright[y+1] > maxright[y])
+						maxright[y] = maxright[y+1];
 				}
+				
+				for (y = 0; y < distance; y++)
+					p[y*bwidth] = MAX2(maxleft[y+distance], maxright[0]);
+				for (; y < bheight-distance; y++)
+					p[y*bwidth] = MAX3(maxleft[y+distance], maxright[y - y%distance], maxright[y-distance]);
+				for (; y < bheight; y++)
+					p[y*bwidth] = MAX2(maxright[y - y%distance], maxright[y-distance]);
 			}
+			delete maxleft;
+			delete maxright;
 		}
+		
 		this->m_cached_buffer = rectf;
 	}
 	unlockMutex();
@@ -421,39 +457,76 @@
 	if (this->m_cached_buffer == NULL) {
 		MemoryBuffer *buffer = (MemoryBuffer *)this->m_inputProgram->initializeTileData(NULL);
 		float *rectf = buffer->convertToValueBuffer();
-		int x, y, i;
+		int x, y;
 		float *p;
 		int bwidth = buffer->getWidth();
 		int bheight = buffer->getHeight();
-		for (i = 0; i < this->m_iterations; i++) {
+
+		int bsize = MAX2(bwidth, bheight);
+		int distance = this->m_iterations;
+		if (distance != 0) {
+			// minleft[i] := minimum of p[i - i%distance] ... p[i], inclusively
+			float *minleft = new float[bsize];
+			// minright[i] := minimum of p[i] ... p[i - i%distance + distance - 1], inclusively
+			// That means, minright[i - i%distance] := minimum of the whole distance-wide block
+			float *minright = new float[bsize];
+			float v;
+			
 			for (y = 0; y < bheight; y++) {
-				for (x = 0; x < bwidth - 1; x++) {
-					p = rectf + (bwidth * y + x);
-					*p = MIN2(*p, *(p + 1));
+				p = rectf + bwidth * y;
+				minleft[0] = minright[0] = p[0];
+				for (x = 1; x < bwidth; x++) {
+					v = p[x];
+					minright[x] = v;
+					if (x % distance && minleft[x-1] < v)
+						minleft[x] = minleft[x-1];
+					else
+						minleft[x] = v;
 				}
-			}
-		
-			for (y = 0; y < bheight; y++) {
-				for (x = bwidth - 1; x >= 1; x--) {
-					p = rectf + (bwidth * y + x);
-					*p = MIN2(*p, *(p - 1));
+				
+				for (x = bwidth-2; x >= 0; x--) {
+					if ((x+1) % distance && minright[x+1] < minright[x])
+						minright[x] = minright[x+1];
 				}
+				
+				// Get the actual minimum as minimum of the current distance-wide block and adequate parts of the neighbors
+				for (x = 0; x < distance; x++)
+					p[x] = MIN2(minleft[x+distance], minright[0]);
+				for (; x < bwidth-distance; x++)
+					p[x] = MIN3(minleft[x+distance], minright[x - x%distance], minright[x-distance]);
+				for (; x < bwidth; x++)
+					p[x] = MIN2(minright[x - x%distance], minright[x-distance]);
 			}
-		
+			
+			// Process all columns in the same manner
 			for (x = 0; x < bwidth; x++) {
-				for (y = 0; y < bheight - 1; y++) {
-					p = rectf + (bwidth * y + x);
-					*p = MIN2(*p, *(p + bwidth));
+				p = rectf + x;
+				minleft[0] = minright[0] = p[0];
+				for (y = 1; y < bheight; y++) {
+					v = p[y*bwidth];
+					minright[y] = v;
+					if (y % distance && minleft[y-1] < v)
+						minleft[y] = minleft[y-1];
+					else
+						minleft[y] = v;
 				}
-			}
-		
-			for (x = 0; x < bwidth; x++) {
-				for (y = bheight - 1; y >= 1; y--) {
-					p = rectf + (bwidth * y + x);
-					*p = MIN2(*p, *(p - bwidth));
+				
+				for (y = bheight-2; y >= 0; y--) {
+					if ((y+1) % distance && minright[y+1] < minright[y])
+						minright[y] = minright[y+1];
 				}
+				
+				for (y = 0; y < distance; y++)
+					p[y*bwidth] = MIN2(minleft[y+distance], minright[0]);
+				for (; y < bheight-distance; y++)
+					p[y*bwidth] = MIN3(minleft[y+distance], minright[y - y%distance], minright[y-distance]);
+				for (; y < bheight; y++)
+					p[y*bwidth] = MIN2(minright[y - y%distance], minright[y-distance]);
 			}
+			delete minleft;
+			delete minright;
 		}
+		
 		this->m_cached_buffer = rectf;
 	}
 	unlockMutex();