How to convert 8-bit RGBA png image to 16 bpc RGBA png image using java 8?

Question

I have used BufferedImage class to generate images from pdf. I am getting 8-bit RGBA by using the below-mentioned snippet, but I was unable to convert it to 16 bpc RGBA.

int page = 0;
BufferedImage bim = new BufferedImage(100, 100, BufferedImage.TYPE_USHORT_565_RGB);
bim = pdfRenderer.renderImage(page);
String fileName = OUTPUT_DIR + "image-" + page + ".png";
ImageIOUtil.writeImage(bim, fileName, 1);

Answer 1

To create a 16 bit per sample (or channel) BufferedImage and store it as a PNG, you can use the following code:

ComponentColorModel colorModel = new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB), true, false, Transparency.TRANSLUCENT, DataBuffer.TYPE_USHORT);
BufferedImage image = new BufferedImage(colorModel, colorModel.createCompatibleWritableRaster(100, 100), colorModel.isAlphaPremultiplied(), null);

if (!ImageIO.write(image, "PNG", new File("test.png"))) {
    System.err.println("Could not write PNG: " + image);
}

From the code, I'm assuming you are using PDFBox. If you are using PDFBox, you can use ImageIOUtil.writeImage instead of ImageIO.write. But you probably want to set the DPI to something more reasonable than 1... 😉

Also note that image = pdfRenderer.renderImage(page) in your code will replace the image, so you can't use that. Try using the renderPageToGraphics(int, Graphics2D)method instead:

ComponentColorModel colorModel = new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB), true, false, Transparency.TRANSLUCENT, DataBuffer.TYPE_USHORT);
BufferedImage image = new BufferedImage(colorModel, colorModel.createCompatibleWritableRaster(100, 100), colorModel.isAlphaPremultiplied(), null);

Graphics2D g = image.createGraphics();
try {
    pdfRenderer.renderPageToGraphics(page, g);
}
finally {
    g.dispose();
}

if (!ImageIOUtil.writeImage(image, test.png, 72))) {
    System.err.println("Could not write PNG: " + image);
}