Make a BufferedImage use less RAM?

Question

I have java program that reads a jpegfile from the harddrive and uses it as the background image for various other things. The image itself is stored in a BufferImage object like so:

BufferedImage background
background = ImageIO.read(file)

This works great - the problem is that the BufferedImage object itself is enormous. For example, a 215k jpeg file becomes a BufferedImage object that's 4 megs and change. The app in question can have some fairly large background images loaded, but whereas the jpegs are never more than a meg or two, the memory used to store the BufferedImage can quickly exceed 100s of megabytes.

I assume all this is because the image is being stored in ram as raw RGB data, not compressed or optimized in any way.

Is there a way to have it store the image in ram in a smaller format? I'm in a situation where I have more slack on the CPU side than RAM, so a slight performance hit to get the image object's size back down towards the jpeg compression would be well worth it.

Answer 1

One of my projects I just down-sample the image as it is being read from an ImageStream on the fly. The down-sampling reduces the dimensions of the image to a required width & height whilst not requiring expensive resizing computations or modification of the image on disk.

Because I down-sample the image to a smaller size, it also significantly reduces the processing power and RAM required to display it. For extra optimization, I render the buffered image in tiles also... But that's a bit outside the scope of this discussion. Try the following:

public static BufferedImage subsampleImage(
    ImageInputStream inputStream,
    int x,
    int y,
    IIOReadProgressListener progressListener) throws IOException {
    BufferedImage resampledImage = null;

    Iterator<ImageReader> readers = ImageIO.getImageReaders(inputStream);

    if(!readers.hasNext()) {
      throw new IOException("No reader available for supplied image stream.");
    }

    ImageReader reader = readers.next();

    ImageReadParam imageReaderParams = reader.getDefaultReadParam();
    reader.setInput(inputStream);

    Dimension d1 = new Dimension(reader.getWidth(0), reader.getHeight(0));
    Dimension d2 = new Dimension(x, y);
    int subsampling = (int)scaleSubsamplingMaintainAspectRatio(d1, d2);
    imageReaderParams.setSourceSubsampling(subsampling, subsampling, 0, 0);

    reader.addIIOReadProgressListener(progressListener);
    resampledImage = reader.read(0, imageReaderParams);
    reader.removeAllIIOReadProgressListeners();

    return resampledImage;
  }

 public static long scaleSubsamplingMaintainAspectRatio(Dimension d1, Dimension d2) {
    long subsampling = 1;

    if(d1.getWidth() > d2.getWidth()) {
      subsampling = Math.round(d1.getWidth() / d2.getWidth());
    } else if(d1.getHeight() > d2.getHeight()) {
      subsampling = Math.round(d1.getHeight() / d2.getHeight());
    }

    return subsampling;
  }

To get the ImageInputStream from a File, use:

ImageIO.createImageInputStream(new File("C:\\image.jpeg"));

As you can see, this implementation respects the images original aspect ratio as well. You can optionally register an IIOReadProgressListener so that you can keep track of how much of the image has been read so far. This is useful for showing a progress bar if the image is being read over a network for instance... Not required though, you can just specify null.

Why is this of particular relevance to your situation? It never reads the entire image into memory, just as much as you need it to so that it can be displayed at the desired resolution. Works really well for huge images, even those that are 10's of MB on disk.