Converting PNG into JPEG

Question

I'm having problems converting a simple PNG into a JPEG format. I'm using the following code:

...

    File png = new File(filePath);
    try {
        SeekableStream s = new FileSeekableStream(png);
        PNGDecodeParam pngParams = new PNGDecodeParam();
        ImageDecoder dec = ImageCodec.createImageDecoder("png", s, pngParams);
        RenderedImage pngImage = dec.decodeAsRenderedImage();
        JPEGEncodeParam jparam = new JPEGEncodeParam();
        jparam.setQuality(0.50f); // e.g. 0.25f
        File jpeg = new File("jpeg.jpeg");
        FileOutputStream out = new FileOutputStream(jpeg);

        ImageEncoder encoder = ImageCodec.createImageEncoder("JPEG", out, jparam); 

        encoder.encode(pngImage);

        s.close();

    } catch (IOException e) {
        ok = false;
        e.printStackTrace();
    }

    return ok;
}

...

I end up with an JAI exception -> java.lang.RuntimeException: Only 1, or 3-band byte data may be written. at com.sun.media.jai.codecimpl.JPEGImageEncoder.encode(JPEGImageEncoder.java:148) ...

Ran out of options. Any suggestion?

Answer 1

It might be easier to use ImageIO to read the PNG into a BufferedImage and write the image out in JPEG format.

Addendum: In this approach, the conversion is handled transparently by the writer's ImageTranscoder.

BufferedImage img = ImageIO.read(new File("image.png"));
ImageIO.write(img, "jpg", new File("image.jpg"));

Answer 2

you probably have alpha channel in the png that you need to get rid of before trying to write the jpg.

Create a new BufferedImage with type TYPE_INT_RGB (not TYPE_INT_ARGB), and then write your source image (pngImage) onto the new blank image.

Something like this (warning, not tested code):

BufferedImage newImage = new BufferedImage( pngImage.getWidth(), pngImage.getHeight(), BufferedImage.TYPE_INT_RGB);
newImage.createGraphics().drawImage( pngImage, 0, 0, Color.BLACK, null);