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  1. #1
    aianta is offline Member
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    Apr 2011
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    Default Drawing an rbg histogram for a picture

    So I'm currently playing around with some code for a project and I want to be able to get a histogram from a picture that shows me the distributions of color in that picture. Now I have a general idea of how this would work but there are some things that are still fuzzy in my head so I would love if someone could look over my idea here and tell me if it has any merit.

    So I want to begin by filling in my histogram with data. If my histogram is represented by a 2d array then it would look something like this:

    Java Code:
    int [] [] histogram = new int [3][255]
    Thus creating a 2d array to hold the 3 bands (RBG) and the frequency of each.

    So I can now create a 2 for loops to loop through my image and for each pixel increase the frequency count for its specific color like this:

    Java Code:
    for ( int i = 0; i < image.width;i++){
    for (int j = 0 ; j < image.height; j++){
    histogram [0] [image.getSample (i,j,0)] ++;
    histogram [1] [image.getSample (i,j,1)] ++;
    histogram [2] [image.getSample (i,j,2)] ++;
    I now have the data for my histogram correct? So here is where I kinda don't know what to do. How do I draw this data? I am not very familiar with Java2D, from my current understanding, I would have to create a new JPanel and create a method there called paint component. But what should I do from there? Draw 255 lines of varying height really close to each other? Also where can I get this graphics g object that seemingly every method that has anything to do with drawing wants?

    Thanks in advance for any help.

  2. #2
    DarrylBurke's Avatar
    DarrylBurke is offline Forum Police
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    Sep 2008
    Madgaon, Goa, India
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    Default Re: Drawing an rbg histogram for a picture

    Sounds like a bar chart, for which you could use JFreeChart. But if you need to do this yourself, go through Lesson: Performing Custom Painting (The Java™ Tutorials > Creating a GUI With JFC/Swing) and Trail: 2D Graphics (The Java™ Tutorials) where all your questions will be answered.

    If you're forever cleaning cobwebs, it's time to get rid of the spiders.

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