imageIO to open .HDR file

Question

I need to open an .hdr file and work on it, but imageIO doesn't supports that format.

The problem is that I need to keep the information loss as little as possible: 32bpc is perfect, 16 is fine and less the 16 won't work.

There are 3 possible solutions I came up to:

1. Find a plugin that allow me to open .HDR file. I've been searching for it a lot but without luck;
2. Find a way to convert the .HDR file to a format I can find a plugin for. Tiff maybe? Tried this too but still no luck;
3. Reduce the dynamic range from 32bpc to 16bpc and then convert it to png. This is tricky because once I have a png file I win, but it's not that easy to cut the range without killing the image..

What would you recommend me to do? Do you know a way to make one of those 3 options works? Or do you have a better idea?

Answer 1

You can now read .HDR using ImageIO. :-)

This is a first version, so it might be a little rough around the edges, but should work for standard (default settings) Radiance RGBE .HDR files.

The returned image will be a custom BufferedImage with a DataBufferFloat backing (ie., samples will be in 3 samples, 32-bit float interleaved RGB format).

By default, a simple global tone-mapping is applied, and all RGB values will be normalized to range [0...1] (this allows anyone to just use ImageIO.read(hdrFile) and the image will look somewhat reasonable, in a very reasonable time).

It is also possible to pass an HDRImageReadParam to the ImageReader instance with a NullToneMapper. This is even faster, but the float values will be unnormalized, and might exceed the max value. This allows you to do custom, more sophisticated tone-mapping on the image data, before converting to something more displayable.

Something like:

// Create input stream
ImageInputStream input = ImageIO.createImageInputStream(hdrFile);

try {
    // Get the reader
    Iterator<ImageReader> readers = ImageIO.getImageReaders(input);

    if (!readers.hasNext()) {
        throw new IllegalArgumentException("No reader for: " + hdrFile);
    }

    ImageReader reader = readers.next();

    try {
        reader.setInput(input);

        // Disable default tone mapping
        HDRImageReadParam param = (HDRImageReadParam) reader.getDefaultReadParam();
        param.setToneMapper(new NullToneMapper());

        // Read the image, using settings from param
        BufferedImage image = reader.read(0, param);
    }
    finally {
        // Dispose reader in finally block to avoid memory leaks
        reader.dispose();
    }
}
finally {
    // Close stream in finally block to avoid resource leaks
    input.close();
}

// Get float data
float[] rgb = ((DataBufferFloat) image.getRaster().getDataBuffer()).getData();

// TODO: Custom tone mapping on float RGB data

// Convert the image to something easily displayable
BufferedImage converted = new ColorConvertOp(null).filter(image, new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_INT_RGB));

// Optionally write as JPEG or other format
ImageIO.write(converted, "JPEG", new File(...));