Comparison of colours in Actionscript 3

In this post I’d like to highlight a topic that is not the classic tip to use everyday but when it needs probably this “recipe” could help.

In last few weeks I had the opportunity to study how to compare 2 or more images and find similar colors between them.
Sincerely when I started I really don’t know how to do that, so I tried to read on the web the best way to accomplish this task.
There are many different way to compare colours, the easiest way that I found it’s working with RGB color space but a lots of experts  advice against this technique and they suggest to run away from RGB color space and work with different color spaces, in particular with which one work in 3D space.
The most complete is for sure the CIELAB so if you need to create an algorithm that compare in the best way colours I really suggest to work with this color space and read this post on this topic, in my case I need something in the middle so a colour space that could guarantee the perfect trade off between complexity and accuracy.
In fact I worked in this example with a 3D space like HSV (Hue, Saturation, Value), before go ahead with the post I warmly suggest to read more about HSV directly on wikipedia.

And now let’s go ahead!!!

I prepare a class that you don’t need to change if the idea behind it fit your needs, so this is the code to compare 2 images with my ColorComparision object:

var util:ColorComparision = new ColorComparision();
var finalDiffArr:Array = util.getSimilars(bmp1.bitmapData, bmp2.bitmapData);

As you can see, in the second line you will receive an Array of colors in RGB that you can use if you want in the UI or only as data if you want to add more complexity to this algorithm.

This comparison is made in this way:

1. I retrieve 64 average colors inside each image (inside the class ColorComparision I set a constant if you need to change this value)
2. I convert each colour from RGB to HSV
3. I calculate the distance between each colour of the first image compared with each colour of the second image

To be more complete as possible I expose also the capability to set the tolerance of the comparison in this way:

util.tollerance = Math.round(slider.value);

Finally I made a quick example where you can play with your images and see what happens, basically in this basic sample when you’ll click “compare” button you will find the color similar between 2 images you will compare.

Last but not least I leave you also this quick method to translate RGB color to HEX  and use them in your Flash application:

function createRect(_obj:Object):Sprite{
 // the obj has 3 properties: r -> red, g -> green, b -> blue
 var intVal:int = _obj.r << 16 | _obj.g << 8 | _obj.b;
 var hex:String = "0x" + intVal.toString(16);

 var s:Sprite = new Sprite();
 s.graphics.beginFill(uint(hex));
 s.graphics.drawRect(0,0, 20, 20);
 s.graphics.endFill();

 return s;

}

On my github space you can find the source to use this algorithm, enjoy!