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SWT: how to make high quality images

My application should resize ImageData. Unfortunately, I did not get the results that I want to get with GC (with anti-aliases and high-level interpolation), or ImageData.scaledTo (). The resulting image is of too low quality to be acceptable. What is the best way to resize an ImageData image?

Edit: I'm zooming out.

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java swt image-resizing
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3 answers

AWT offers image scaling with various modes. To zoom out, Average area averaging offers the best quality. Of course, it would be possible to re-implement the algorithm for scaling the averaging region for SWT or for a quick solution, which is often enough:

  • convert SWT image to AWT image
  • change the scale using the corresponding mode (averaging over the area, if zooming, bilinear otherwise)
  • convert it back to SWT image

Code for converting between SWT and AWT images can be found here .

/** * Resizes an image, using the given scaling factor. Constructs a new image resource, please take care of resource * disposal if you no longer need the original one. This method is optimized for quality, not for speed. * * @param image source image * @param scale scale factor (<1 = downscaling, >1 = upscaling) * @return scaled image */ public static org.eclipse.swt.graphics.Image resize (org.eclipse.swt.graphics.Image image, float scale) { int w = image.getBounds().width; int h = image.getBounds().height; // convert to buffered image BufferedImage img = convertToAWT(image.getImageData()); // resize buffered image int newWidth = Math.round(scale * w); int newHeight = Math.round(scale * h); // determine scaling mode for best result: if downsizing, use area averaging, if upsizing, use smooth scaling // (usually bilinear). int mode = scale < 1 ? BufferedImage.SCALE_AREA_AVERAGING : BufferedImage.SCALE_SMOOTH; java.awt.Image scaledImage = img.getScaledInstance(newWidth, newHeight, mode); // convert the scaled image back to a buffered image img = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB); img.getGraphics().drawImage(scaledImage, 0, 0, null); // reconstruct swt image ImageData imageData = convertToSWT(img); return new org.eclipse.swt.graphics.Image(Display.getDefault(), imageData); } public static BufferedImage convertToAWT (ImageData data) { ColorModel colorModel = null; PaletteData palette = data.palette; if (palette.isDirect) { colorModel = new DirectColorModel(data.depth, palette.redMask, palette.greenMask, palette.blueMask); BufferedImage bufferedImage = new BufferedImage(colorModel, colorModel.createCompatibleWritableRaster(data.width, data.height), false, null); WritableRaster raster = bufferedImage.getRaster(); int[] pixelArray = new int[3]; for (int y = 0; y < data.height; y++) { for (int x = 0; x < data.width; x++) { int pixel = data.getPixel(x, y); RGB rgb = palette.getRGB(pixel); pixelArray[0] = rgb.red; pixelArray[1] = rgb.green; pixelArray[2] = rgb.blue; raster.setPixels(x, y, 1, 1, pixelArray); } } return bufferedImage; } else { RGB[] rgbs = palette.getRGBs(); byte[] red = new byte[rgbs.length]; byte[] green = new byte[rgbs.length]; byte[] blue = new byte[rgbs.length]; for (int i = 0; i < rgbs.length; i++) { RGB rgb = rgbs[i]; red[i] = (byte) rgb.red; green[i] = (byte) rgb.green; blue[i] = (byte) rgb.blue; } if (data.transparentPixel != -1) { colorModel = new IndexColorModel(data.depth, rgbs.length, red, green, blue, data.transparentPixel); } else { colorModel = new IndexColorModel(data.depth, rgbs.length, red, green, blue); } BufferedImage bufferedImage = new BufferedImage(colorModel, colorModel.createCompatibleWritableRaster(data.width, data.height), false, null); WritableRaster raster = bufferedImage.getRaster(); int[] pixelArray = new int[1]; for (int y = 0; y < data.height; y++) { for (int x = 0; x < data.width; x++) { int pixel = data.getPixel(x, y); pixelArray[0] = pixel; raster.setPixel(x, y, pixelArray); } } return bufferedImage; } } public static ImageData convertToSWT (BufferedImage bufferedImage) { if (bufferedImage.getColorModel() instanceof DirectColorModel) { DirectColorModel colorModel = (DirectColorModel) bufferedImage.getColorModel(); PaletteData palette = new PaletteData(colorModel.getRedMask(), colorModel.getGreenMask(), colorModel.getBlueMask()); ImageData data = new ImageData(bufferedImage.getWidth(), bufferedImage.getHeight(), colorModel.getPixelSize(), palette); WritableRaster raster = bufferedImage.getRaster(); int[] pixelArray = new int[3]; for (int y = 0; y < data.height; y++) { for (int x = 0; x < data.width; x++) { raster.getPixel(x, y, pixelArray); int pixel = palette.getPixel(new RGB(pixelArray[0], pixelArray[1], pixelArray[2])); data.setPixel(x, y, pixel); } } return data; } else if (bufferedImage.getColorModel() instanceof IndexColorModel) { IndexColorModel colorModel = (IndexColorModel) bufferedImage.getColorModel(); int size = colorModel.getMapSize(); byte[] reds = new byte[size]; byte[] greens = new byte[size]; byte[] blues = new byte[size]; colorModel.getReds(reds); colorModel.getGreens(greens); colorModel.getBlues(blues); RGB[] rgbs = new RGB[size]; for (int i = 0; i < rgbs.length; i++) { rgbs[i] = new RGB(reds[i] & 0xFF, greens[i] & 0xFF, blues[i] & 0xFF); } PaletteData palette = new PaletteData(rgbs); ImageData data = new ImageData(bufferedImage.getWidth(), bufferedImage.getHeight(), colorModel.getPixelSize(), palette); data.transparentPixel = colorModel.getTransparentPixel(); WritableRaster raster = bufferedImage.getRaster(); int[] pixelArray = new int[1]; for (int y = 0; y < data.height; y++) { for (int x = 0; x < data.width; x++) { raster.getPixel(x, y, pixelArray); data.setPixel(x, y, pixelArray[0]); } } return data; } return null; }
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The decision is not about transparency. Here is a snippet that I came across that does high-quality resizing and preserves transparency:

 public static Image resize(Image image, int width, int height) { Image scaled = new Image(Display.getDefault(), width, height); GC gc = new GC(scaled); gc.setAntialias(SWT.ON); gc.setInterpolation(SWT.HIGH); gc.drawImage(image, 0, 0,image.getBounds().width, image.getBounds().height, 0, 0, width, height); gc.dispose(); image.dispose(); // don't forget about me! return scaled; }

I found it here:

http://aniszczyk.org/2007/08/09/resizing-images-using-swt/

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We had success with ImageMagick / JMagick. http://www.jmagick.org/index.html

The only problem is that if the images are uploaded by users and you have a large user base, you will have memory leaks due to invalid image files, etc.

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