Resizing image and looks bad afterward

Question

So image manipulation in java is not my bag. I wrote a program to help save me time with my photography, the idea was that I could point it at a directory and then it would read all the files in that folder that are jpgs and resize them to blog ready sizes. This works really well cept the final images that are produced are not of same quality as say when I used GIMP to resize to the same size/aspect ratio the quality is much different. It looks like its a problem with setting my type perhaps to an only 8bit file? Maybe I am wrong, also goofed with the compression stuff (found code online) to turn the compression to 0 (i.e. no compression)...still no avail. Some code I am using:
    public static BufferedImage scaleImage(BufferedImage image, int imageType,
                 int newWidth, int newHeight) {
             // Make sure the aspect ratio is maintained, so the image is not distorted
             double aspectRatio = (double) image.getWidth() / (double) image.getHeight();
              if(newWidth==-1)
                   newWidth=(int)(newHeight * aspectRatio);
              if(newHeight==-1)
                   newHeight = (int)(newWidth / aspectRatio);
             // Draw the scaled image
             BufferedImage newImage = new BufferedImage(newWidth, newHeight,
                     imageType);
             Graphics2D graphics2D = newImage.createGraphics();
                //I admit little clue as to what im doing with the rendering hints.
             Map map = new HashMap();
             map.put(RenderingHints.KEY_INTERPOLATION,
             RenderingHints.VALUE_INTERPOLATION_BILINEAR);
             map.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
             map.put(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
             RenderingHints hints = new RenderingHints(map);
             graphics2D.setRenderingHints(hints);
             graphics2D.drawImage(image, 0, 0, newWidth, newHeight, null);
             return newImage;
    then the call to it looks like:
public BufferedImage processLandScapeImage(BufferedImage img)
              int width = Integer.valueOf(theHeight.getText()).intValue(); //my desired width
              return scaleImage(img, BufferedImage.TYPE_INT_RGB, width, -1);
         }So this is close, the files dont look bad but alas... they still aren't the same quality. Should I post a sample of what I get with GIMP and what I get with my little program?
Thanks to anyone who has some pointers...
-Shane

Answer 1

If you don't care about the original source BufferedImage, then you should be able to draw the image onto itself in an incremental fashion. That would avoid the use of intermediate images and consequently not throw the OOM.
Also note that the code in that article has a slight hiccup. If you specify you want higher quality and targetWidth > w || targetHeight > h, then you'll get an infinite loop. So it needs to be structured slightly different (indeed, the intermediate images should probably be flushed since they're being draw to and from at least once).
I didn't realize such a task was so non-trivial.If you're not worried about the speed, then I guess the trivial good-result way would be to use Image#getScaledInstance with the area average parameter. It's not so much that it's too slow for normal consumption (it isn't), it's just that the Graphics way is so much faster.
GIMP probably uses a more sophisticated resampling technique like Lanczos or something.