This is my function to resize images. The quality is not photoshop but it's acceptable.
What's not acceptable is the behaviour on indexed png.
We expect that if we scale down an image with a 256 colors palette with a transparent index we would get a resized image with same transparency, but this it not the case.
So we did the resize on a new ARGB image and then we reduce it to 256 colors. The problem is how to "reintroduce" the transparent pixel index.
private static BufferedImage internalResize(BufferedImage source, int destWidth, int destHeight) {
int sourceWidth = source.getWidth();
int sourceHeight = source.getHeight();
double xScale = ((double) destWidth) / (double) sourceWidth;
double yScale = ((double) destHeight) / (double) sourceHeight;
Graphics2D g2d = null;
BufferedImage resizedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TRANSLUCENT);
log.debug("resizing image to w:" + destWidth + " h:" + destHeight);
try {
g2d = resizedImage.createGraphics();
g2d.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_QUALITY);
g2d.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
AffineTransform at = AffineTransform.getScaleInstance(xScale, yScale);
g2d.drawRenderedImage(source, at);
} finally {
if (g2d != null)
g2d.dispose();
}
//doesn't keep the transparency
if (source.getType() == BufferedImage.TYPE_BYTE_INDEXED) {
log.debug("reducing to color-indexed image");
BufferedImage indexedImage = new BufferedImage(destWidth, destHeight, BufferedImage.TYPE_BYTE_INDEXED);
try {
Graphics g = indexedImage.createGraphics();
g.drawImage(resizedImage, 0, 0, null);
} finally {
if (g != null)
g.dispose();
}
System.err.println("source" + ((IndexColorModel) source.getColorModel()).getTransparentPixel()
+ " " + ((IndexColorModel) indexedImage.getColorModel()).getTransparentPixel());
return indexedImage;
}
return resizedImage;
}