Question on image analysis.

Question

Hi,
I looked into tutorials on Java2D which teaches me on transforming images.
But I want to analyse images (in common formats like JPEG). For example, I
want to get, say, % of area in yellow color, % in red, green etc. Something
like that. I presume this would require to read the image line by line,
pixel by pixel and get the attributes (color) of each pixel. Is it the
correct direction for me to study tutorials on iostream (to read the image
file)?
Any guidelines and reference for me?
thanks in advance,
jackling.

Answer 1

I haven't kept up with the new fangled java image stuff, but the way I used to play with pixels was as follows:
pixelArray = new int[width * height];
try{
       pixelGrab = new PixelGrabber(rawImage,0,0,width,height,pixelArray,0,width);
            if(pixelGrab.grabPixels() && ((pixelGrab.getStatus() & ImageObserver.ALLBITS) != 0)){
            } else {
                //throw some kind of exception
        } catch(InterruptedException e) {
            System.out.println("MapInteraction::ripImage ~ failed to grab pixels from image");
    }then you can do manipulations using the ARGB channels for each individual pixel. The array that is generated holds scan lines of the original image in sequence, so therefore pixel 1,1 (from top left, starting @ 0,0) would be @ pixelArray[width*1 + 1].
Example of bit analysis using bitwise operators:
if ( (pixelArray[y*width + x] & 0x00FF0000) == 0x00FF0000 ) {
Make sure your in 32-bit colour resolution when you do the ripping. I've had issues in the past when I was doing analysis expecting 32-bit mode and forgetting to set it!!