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  1. #1
    JeroenV is offline Member
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    Default Comparing blue values

    Hello,

    I'm trying to save all the blue values from a certain part of my screen into an arraylist (pixel int). However I got into some things/problems that I don't understand. First of all, here's my code:

    Java Code:
            
            Rectangle area = new Rectangle(1181,128,37,37);
            
            BufferedImage bi = r.createScreenCapture(area);
            ColorModel cm = bi.getColorModel();
            
            ArrayList<Integer> pix = new ArrayList<Integer>();
            
            for(int i=0;i<=1000;i++){
            	if(cm.getBlue(i) >= 200){
            		pix.add(i);
            	}
            }
    I know that getBlue() returns the RGB value between 0- .. 250 I believe. However it looks like almost every pixel is over 200 blue value.. I don't understand why because on the image itself you can clearly see that there are pixels that are blue and the rest is more green/white.

    Another thing I'm noticing is that no matter how big I make the for loop it will still give me values. So that made me wonder how many pixels a 37x37 square actually has..



    Thanks in advance,
    Jeroen V.

  2. #2
    AndrewM16921 is offline Senior Member
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    Default Re: Comparing blue values

    Blue can be from 0 to 255 (8 bits, 2^8=256)
    Also, white is (255, 255, 255) so it has a full blue component.
    Last edited by AndrewM16921; 10-06-2013 at 06:46 AM.

  3. #3
    JeroenV is offline Member
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    Default Re: Comparing blue values

    So how do I only get the blue values and how many pixels does a 37x37 square have?

    Edit:
    I don't get this.

    First of all I'm trying to create the image of a square by using this code (which should just create a screen capture around that area)
    Java Code:
            Rectangle area = new Rectangle(1181,128,37,37);
            BufferedImage bi = r.createScreenCapture(area);
    After that I turn it into a ColorModel that I could compare the blue values of:
    Java Code:
            ColorModel cm = bi.getColorModel();
    Now I judge from the fact that square is 37x37, it would have 1369 pixels. So I create a for loop to go through all the pixels and see what their blue value is like:
    Java Code:
            ArrayList<Integer> pix = new ArrayList<Integer>();
           
            for(int i=0;i<=1369;i++){
                pix.add(cm.getBlue(i));
            }
    and this is what it returns:

    Java Code:
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    ...
    That is what it returns for this image: http://prntscr.com/1vk034

    What am I doing wrong here?

    The thing I'm trying to accomplish is for my program to recognize if the blue pointer is pointing in the same direction as the picture itself. So if in the image it's pointing south I could use a method to check if the live pointer is also pointing south.
    Last edited by JeroenV; 10-06-2013 at 07:34 AM.

  4. #4
    JosAH's Avatar
    JosAH is offline Moderator
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    Default Re: Comparing blue values

    That is not how ColorModels work; they model a color (such as RGB values), they're not a 'gateway' to the image. Get the RGB values from your BufferedImage directly (read the API documentation for that class) and get the blue value out of the int representing AARRGGB.

    kind regards,

    Jos
    cenosillicaphobia: the fear for an empty beer glass

  5. #5
    Tolls is offline Moderator
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    Default Re: Comparing blue values

    Quote Originally Posted by JeroenV View Post
    So how do I only get the blue values ...?
    You'll need to define "blue" for the purposes of your application.
    That is, what ranges of RGB would classify as blue.
    Over 200 on B, but under 50 on R and G?
    Note those figures are made up...I have no idea what colours that would actually give you.
    Please do not ask for code as refusal often offends.

    ** This space for rent **

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