Help me out with Counting Colours

[inox]

Hi Everyone,

This had wandering over me for weeks now. Any help is very much appreciated.

I am working on image processing stuff now. I am now required to count the number of unique colours in an image so that I can identify few prominent colours to be my threshold values for further image segmentation.

I am working this out with both Java and JIU (Java Imaging Utilities) and able to get each pixel R,G and B value out. My problem is how can I put these values together and compare each pixel colour to another so that one which is similar will be ignored. I know that I can make use of Set as well as ArrayList even Vector in order to count these colours but not sure which one is better to use.

Hope u guys can help me out with this :-)

inox

[Belisarius]

How about creating your own Pixel object that implements Comparable? Define equals() and compareTo(), and then shove them into a Set of some sort (doesn't really matter which type). A Set will ignore duplicates, so all of the elements will be unique.

[sde]

it sounds like he also needs to setup a way to count how many times that RGB value has been counted if he wants to identify the 'prominent' colors.

[teknomage1]

This might be easier to visulaize if you move it form RGB color space to Hue, Saturation, and Value colorspace. That way you can set thresholds for each dimension rather than having to remember that green is 30% stronger in our perception of color and that blue is going to be inherently darker than red in terms of color perception.

EDIT: Just for reference Hue is what actual color you see, such as red or magenta, or yellow. Saturation is the amount of color in it a saturation of zero is a grayscale image whereas a full saturation would yield pure color. Value represents how light or dark the color is.

[inox]

Hi Teknomage1,

I actually had thought about using Hue rather than to consider the RGB values. Indeed by using hue it makes my life easier. One question though, will it be correct if I am using hue so as to count distinct colour in an image? I have tried this and had a number but not sure whether the amount is correct. Or do I need to consider both saturation and value as well?

Thank you and hoping to hear from you.

~inox

[teknomage1]

It depends on how limited you want your palette, but I would consider all three values. A change in hue will have the greatest impact of course, but a blue with full value will look very different than one with half value and same for saturation. I'm not sure if there are algorythms for this, but to get an idea of how it all works together maybe you should just play with the color picker of your favorite image editting program. By playing with the visual display you can get an idea for your tolerance ranges.