Reading grayscale values from saved image

Question

Hi,
I've written several methods that crop, convert to grayscale, histogram equalise and then resize a colour jpeg image for preparing sets of images for a face detection neural network. The next thing I want to do is to write a method that allows me to read that saved grayscale images pixel values back as singular grayscale values from the RGB values that were used to save the jpeg. I used this code to create the 2D array of grayscale pixel values
      for (int i = 0; i < imageWidth; i++)
            for (int j=0; j <imageHeight; j++)
                grayRGB[i][j] = (rgb[i][j] & 0xff000000) | (eqGray[i][j]<<16) | (eqGray[i][j]<<8) | (eqGray[i][j]);
                img.setRGB(i, j, grayRGB[i][j]);
            }and then used this code to resize the image:
        BufferedImage resized = new BufferedImage(20,20,1);
        Graphics2D g = resized.createGraphics();
        g.drawImage(img, 0, 0, 20, 20, null);
        g.dispose();my class gets the RGB values on instantiation as follows:
        //get RGB pixel values for image loaded
        for (int i = 0; i < imageWidth; i++)
            for (int j=0; j <imageHeight; j++)
                rgb[i][j]= inputImage.getRGB(i,j);
                //perform bitwise shift rgb information values to obtain appropriate values for each colour pixel
                r[i][j]=  (rgb[i][j] >> 16) &0xff;
                g[i][j]=  (rgb[i][j] >> 8) &0xff;
                b[i][j]=  (rgb[i][j]) &0xff;
            }Is there a way to get the grayscale values directly from an image that is already converted to grayscale without having to perform the grayscale conversion method again, perhaps using a similar bitwise shift?
Thanks
Nick

Answer 1

answering this myself for those lost souls like i was a while ago:
the answer is very simple when you get to know it :) : use a signed type for your image. this can be achieved by using the Format Operator (javax.media.jai.operator.FormatDescriptor). an example as follows :
        BufferedImage bufferedImage= someimage...
        ParameterBlock pb = new ParameterBlock();
        pb.addSource(bufferedImage);
        pb.add(DataBuffer.TYPE_SHORT);
        RenderedImage formattedImage =
                JAI.create("format", pb, null);
// you may use as well TYPE_DOUBLE or TYPE_FLOATimage could be of any type such as PlanarImage, BufferedImage, RenderedImage etc..
then all you need to do is read your pixel values by using an iterator such as RectIter or RandomIter to access pixel values etc..
San