Vary JPEG2000 compression levels by icon size for quality improvements

High JPEG2000 compression levels result in excellent results at large
image dimensions, but can cause very visible artefacting for smaller
icon dimensions.  This commit applies the specified compression level
for the large image sizes, applies less compression for 512*512 and
256*256 sizes, and disables compression for smaller sizes; this allows
JPEG2000 compression to be increased overall for much smaller file
sizes with no visible loss in quality, producing excellent output at
compression levels of 0.2-05 for most icons.

Also outputs the compression level being used for each size in the
output.

oldiconutil/main.m

@@ -31,7 +31,8 @@ int main(int argc, const char * argv[])
 	BOOL					convertInPlace = NO;
 	BOOL					listOnly = NO;
 	int						nameArgumentPosition = 1;
-	NSNumber*				jpegCompressionObj = [NSNumber numberWithFloat: 1.0];
+	float					jpegCompressionLevel = 1.f;
+	NSNumber*				jpegCompressionObj = [NSNumber numberWithFloat: jpegCompressionLevel];
 	NSBitmapImageFileType	compressionType = NSJPEG2000FileType;
 	NSString*				destCompression = @"jp2";
 
@@ -94,11 +95,10 @@ int main(int argc, const char * argv[])
 			}
 		}
 
-		// If a compression level has been specified, parse it from the remaining string and use it:
+		// If a compression level has been specified, parse it from the remaining string:
 		if( compStr.length > 0 )
 		{
-			float			theCompression = [compStr floatValue];
-			jpegCompressionObj = [NSNumber numberWithFloat: theCompression];
+			jpegCompressionLevel = [compStr floatValue];
 		}
 	}
 
@@ -173,9 +173,37 @@ int main(int argc, const char * argv[])
 
 					if( shouldConvert )
 					{
+
+						// For JPEG2000, high compression levels work very well for large sizes,
+						// but cause very visible artefacts at smaller sizes.  So if using JPEG2000
+						// output format, don't apply compression for small sizes; use the specified
+						// compression for the largest 1024*1024 (ic10) size, and use less compression
+						// for medium sizes.
+						float jpegCompressionForSize = jpegCompressionLevel;
+						if ( [destCompression isEqualToString:@"jp2"] ) {
+
+							// Use no compression for the smallest sizes (ic11: 16*16@2x; ic12: 32*32@2x, ic07: 128*128)
+							if ( strcmp(blockType, "ic11") == 0 || strcmp(blockType, "ic12") == 0 || strcmp(blockType, "ic07") == 0 ) {
+								jpegCompressionForSize = 1.f;
+
+							// For the 256*256 sizes, halve the compression level (ic08: 256*256; ic13: 128*128@2x)
+							} else if ( strcmp(blockType, "ic08") == 0 || strcmp(blockType, "ic13") == 0 ) {
+								jpegCompressionForSize = (jpegCompressionForSize + 1.f) / 2.f;
+
+							// For the 512*512 sizes, use three-quarter compression (ic09: 512*512, ic14: 256*256@2x)
+							} else if ( strcmp(blockType, "ic09") == 0 || strcmp(blockType, "ic14") == 0 ) {
+								jpegCompressionForSize = ((jpegCompressionForSize * 3) + 1.f) / 4.f;
+							}
+						}
+						jpegCompressionObj = [NSNumber numberWithFloat: jpegCompressionForSize];
+
 						if( !listOnly )
 						{
-							printf( "\tConverting PNG to %s\n", [destCompression UTF8String] );
+							if ( [destCompression isEqualToString:@"jp2"] || [destCompression isEqualToString:@"jpg"] ) {
+								printf( "\tConverting PNG to %s (JPEG compression %f)\n", [destCompression UTF8String], jpegCompressionForSize );
+							} else {
+								printf( "\tConverting PNG to %s\n", [destCompression UTF8String] );
+							}
 
 							NSBitmapImageRep	*	theImage = [[NSBitmapImageRep alloc] initWithData: currBlockData];
 							NSData				*	jp2Data = [theImage representationUsingType: NSJPEG2000FileType properties: