Fixed issue where scaling of lesser or poorly supported file types in Java2D (e.g. GIF)

produce terrible-looking results. Now all scaled results look good.

This was fixed for all quality levels by forcing all resultant images into either an
RGB or RGBA image type.

Author: Riyad Kalla

src/main/java/com/thebuzzmedia/imgscalr/Scalr.java

@@ -16,7 +16,9 @@
 package com.thebuzzmedia.imgscalr;
 
 import java.awt.Graphics2D;
+import java.awt.Image;
 import java.awt.RenderingHints;
+import java.awt.Transparency;
 import java.awt.image.BufferedImage;
 
 /**
@@ -81,8 +83,30 @@
  * on any of the <em>source images</em> passed in by calling code; it is up to
  * the original caller to dispose of their source images when they are no longer
  * needed so the VM can most efficiently GC them.
+ * <h3>Generated Image Types</h3>
+ * Java2D provides support for a number of different image types defined as
+ * <code>BufferedImage.TYPE_*</code> variables, unfortunately not all image
+ * types are supported equally in Java2D. Some more obscure image types either
+ * have poor or no support, leading to severely degraded quality when an attempt
+ * is made by imgscalr to create a scaled instance <em>of the same type</em> as
+ * the source image.
  * <p/>
- * <strong>Logging</strong>: This class implements all its debug logging via the
+ * To avoid imgscalr generating significantly worse-looking results than
+ * alternative scaling approaches (e.g.
+ * {@link Image#getScaledInstance(int, int, int)}), all resultant images
+ * generated by imgscalr are of one of two types:
+ * <ol>
+ * <li>{@link BufferedImage#TYPE_INT_RGB}</li>
+ * <li>{@link BufferedImage#TYPE_INT_ARGB}</li>
+ * </ol>
+ * depending on if the source image utilizes transparency or not.
+ * <p/>
+ * This is a recommended approach by the Java2D team for dealing with poorly (or
+ * non) supported image types. More can be read about this issue <a href=
+ * "http://www.mail-archive.com/java2d-interest@capra.eng.sun.com/msg05621.html"
+ * >here</a>.
+ * <h3>Logging</h3>
+ * This class implements all its debug logging via the
  * {@link #log(String, Object...)} method. At this time logging is done directly
  * to <code>System.out</code> via the <code>printf</code> method. This allows
  * the logging to be light weight and easy to capture.
@@ -327,7 +351,7 @@ public static BufferedImage resize(BufferedImage src, Method scalingMethod,
 			float ratio = ((float) currentHeight / (float) currentWidth);
 
 			if (DEBUG)
-				log("Resizing Source Image [size=%dx%d, orientation=%s, ratio(H/W)=%f] to [targetSize=%dx%d]",
+				log("START Resizing Source Image [size=%dx%d, orientation=%s, ratio(H/W)=%f] to [targetSize=%dx%d]",
 						currentWidth, currentHeight,
 						(ratio <= 1 ? "landscape/square" : "portrait"), ratio,
 						targetWidth, targetHeight);
@@ -346,6 +370,10 @@ public static BufferedImage resize(BufferedImage src, Method scalingMethod,
 			 * mangling the result.
 			 */
 			if (ratio <= 1) {
+				// First make sure we need to do any work in the first place
+				if (targetWidth == src.getWidth())
+					return src;
+
 				// Save for detailed logging (this is cheap).
 				int originalTargetHeight = targetHeight;
 
@@ -360,6 +388,10 @@ public static BufferedImage resize(BufferedImage src, Method scalingMethod,
 					log("Auto-Corrected targetHeight [from=%d to=%d] to honor image proportions",
 							originalTargetHeight, targetHeight);
 			} else {
+				// First make sure we need to do any work in the first place
+				if (targetHeight == src.getHeight())
+					return src;
+
 				// Save for detailed logging (this is cheap).
 				int originalTargetWidth = targetWidth;
 
@@ -436,7 +468,7 @@ public static BufferedImage resize(BufferedImage src, Method scalingMethod,
 
 			if (DEBUG) {
 				long elapsedTime = System.currentTimeMillis() - startTime;
-				log("Source Image Scaled from [%dx%d] to [%dx%d] in %d ms (approx %f seconds)",
+				log("END Source Image Scaled from [%dx%d] to [%dx%d] in %d ms (approx %f seconds)",
 						currentWidth, currentHeight, targetWidth, targetHeight,
 						elapsedTime, (double) elapsedTime / (double) 1000);
 			}
@@ -548,9 +580,32 @@ else if (length <= BALANCED_SPEED_THRESHOLD_PX)
 	 */
 	protected static BufferedImage scaleImage(BufferedImage src,
 			int targetWidth, int targetHeight, Object interpolationHintValue) {
+		/*
+		 * Determine the TYPE of image (plain RGB or RGB + Alpha) that we want
+		 * to render the scaled instance into. We force all rendering results
+		 * into one of these two types, avoiding the case where a source image
+		 * is of an unsupported (or poorly supported) format by Java2D and the
+		 * written results, when attempting to re-create and write out that
+		 * format, is garbage.
+		 * 
+		 * Originally reported by Magnus Kvalheim from Movellas when scaling
+		 * certain GIF and PNG images.
+		 * 
+		 * More information about Java2D and poorly supported image types:
+		 * http:/
+		 * /www.mail-archive.com/java2d-interest@capra.eng.sun.com/msg05621.html
+		 * 
+		 * Thanks to Morten Nobel for the implementation hint:
+		 * http://code.google
+		 * .com/p/java-image-scaling/source/browse/trunk/src/main
+		 * /java/com/mortennobel/imagescaling/MultiStepRescaleOp.java
+		 */
+		int imageType = (src.getTransparency() == Transparency.OPAQUE ? BufferedImage.TYPE_INT_RGB
+				: BufferedImage.TYPE_INT_ARGB);
+
 		// Setup the rendering resources to match the source image's
 		BufferedImage result = new BufferedImage(targetWidth, targetHeight,
-				src.getType());
+				imageType);
 		Graphics2D resultGraphics = result.createGraphics();
 
 		// Scale the image to the new buffer using the specified rendering hint.