Replace a region of an image

[alex88]

Hi guys, i've to do a parallel image processing, i'm making the basics of that, so i've created a function that returns a region of a jpeg file as bufferedImage, this way:

BufferedImage image = readImg("/Users/alessandro/Documents/image.jpg", 0,0,8,8);

That will return the image region starting at (0,0) having width and height as 8px.

Now after processing (converting or what else) i've lot of these chunks to reassemble in the final image, i've managed to create an empty image having the same size of the original one (as jpeg) and i'm trying to replace block by block the regions of the final image with this code:

public static void writeImg (String path, int startx, int starty, BufferedImage image){
		File output = new File(path);
		ImageOutputStream ios = null;
		try {
			ios = ImageIO.createImageOutputStream(output);
		} catch (IOException e){
			e.printStackTrace();
		}
		Iterator iter = ImageIO.getImageWritersByFormatName("BMP");
		ImageWriter writer = (ImageWriter)iter.next();
		writer.setOutput(ios);
		
		try{
			if(writer.canReplacePixels(0)){
				System.out.println("True");
			}else{
				System.out.println("False");
			}
		}catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		ImageWriteParam param = writer.getDefaultWriteParam();
		Point destinationOffset = new Point(startx,starty);
		param.setDestinationOffset(destinationOffset);
		try {
			writer.replacePixels(image, param);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

the problem is that

writer.replacePixels(image, param);

throws "java.lang.UnsupportedOperationException: Unsupported write variant!" and i've no idea why and how could i fix this error, any idea?

[toadaly]

If you read the API for ImageWriter, you'll notice that 'replacePixels' is an optional feature that throws UnsupportedOperationException if it's not supported. The ImageWriter you are using doesn't support 'replacePixels', so you'll have to find another way.

I suggest forming the output image as a BufferedImage, and not writing it out until it's complete.

[alex88]

Thank you for response, bytheway that's the problem, the final image (as the source one) is too big to fit in memory, i wanted to do that on a cluster using map reduce, and assign each worker the operation to get its own block, process it and write the result.

[zahariesergiu]

hello Alex, i have the same problem,did you resolve it?
please let me now. Thank you!

[alex88]

Not really i'm sorry, you should check at JPEGclub.org to see some source in C and probably with that it can be done without decoding the full image.