Java image scaling without loading the whole image into memory

问题

We have some very large jpgs which are used when print on A0 printers.

The problem is that we need to convert this large image down to a thumbnail for use in a few java UIs.

Is there any way to convert the image (with Java) without loading the whole image into memory? Currently we get out of memory exceptions when we try to load the images.

Is there anything in the standard code or is my best bet to use jmagick? A pure java implementation would be best for our deployment.

Thanks

回答1:

I managed to get it working and the full code is as follows.

The call to reader.setInput(iis, true, true); is the magic which I was missing from the previous post.

FileInputStream fin = new FileInputStream(source);

ImageInputStream iis = ImageIO.createImageInputStream(fin);

Iterator iter = ImageIO.getImageReaders(iis);
if (!iter.hasNext()) {
    return;
}

ImageReader reader = (ImageReader) iter.next();

ImageReadParam params = reader.getDefaultReadParam();

reader.setInput(iis, true, true);

params.setSourceSubsampling(width, height, 0, 0);

BufferedImage img = reader.read(0, params);

ImageIO.write(img, "JPG", destination);

来源：https://stackoverflow.com/questions/10817597/java-image-scaling-without-loading-the-whole-image-into-memory