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Understanding AS3 ColorMatrixFilter class

Emanuele Feronato Actionscript 3, Flash

Do you want to apply color correction to images into your Flash movies on the fly?

Then ColorMatrixFilter is the class you need.

The ColorMatrixFilter class lets you apply a 4 x 5 matrix transformation on the RGBA color and alpha values of every pixel in the input image to produce a result with a new set of RGBA color and alpha values.

The color matrix filter separates each source pixel into its red, green, blue, and alpha components as srcR, srcG, srcB, srcA.

To calculate the result of each of the four channels, the value of each pixel in the image is multiplied by the values in the transformation matrix.

It allows saturation changes, hue rotation, luminance to alpha, and various other effects.

For more information visit the official Adobe docs page.

Around the web you can find a lot of examples of photos loaded with Flash and sliders to change colors, but I want to explore this feature from a coding point of view.

I will make some experiment on this photo I found on Flickr

The first thing is creating a MovieClip with the image inside. I called it cats, so with this simple code I display the cats on the stage:

nothing new… now it’s time to add the filter.

Now let’s try this script:

multiplying all values by 0.5, we have a standard (and not so interesting) black and white photo.

While with this script

we have no changes. Why not? because the matrix is an identity matrix.

An identity matrix or unit matrix of size n is the n-by-n square matrix with ones on the main diagonal and zeros elsewhere.

Changing the saturation

To change the saturation of an image, simply boost red component on red channel, green component on green channel and blue component on blue channel, while decreasing the other ones.

Adding contrast

To add contrast, increase red component on red channel, green component on green channel and blue component on blue channel and decrease all offset values, this way

Changing the hue

To change the hue, swap red, green and blue values

Obviously you must finetune your matrix in order to achieve the best effect, but now you know how to change colors on the fly.

Download the source code and play with the values.

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Comments 19

  1. tolleder

    The description for changing saturation sound for me more like:

    matrix=matrix.concat([2,-1,-1,0,0]);// red
    matrix=matrix.concat([-1,2,-1,0,0]);// green
    matrix=matrix.concat([-1,-1,2,0,0]);// blue
    matrix=matrix.concat([0,0,0,1,0]);// alpha

    Also in Photoshop I never reach such red hair by just changing saturation.

  2. gremlinc5

    @Emanuele: great tips!

    I would like to point out just a this:
    the overall lightness of the resulting image depends on the SUM of the values on each row (so, Tolleder, your filter would produce a much darker image).

    In order to mantain the original luminosity (for each channel), each row must sum to 1.

    So, a better b&w filter matrix would be:
    0.3 0.6 0.1 0 0
    0.3 0.6 0.1 0 0
    0.3 0.6 0.1 0 0
    0 0 0 1 0
    This would retain luminance and would take account that blue is darker than red and green.

    @Tolleder: in Photoshop (and Gimp) the appropriate filter is the Channel Mixer, which applies exactly the same calculations to the image.

    Keep up with the good work!

  3. Yair Neumann

    I used the code in the first segment to turn a photo into b/w . the only difference is that in my FLA the photo is on the stage and not created by code.

    i used the “this” property to call on all the objects that are connected to my class and ran the function deSat wich had all the code in the upper segment.

    when I ran the SWF file the pictures disapeared…
    Do you have an explanation how this could happen?

  4. Rahul Desai

    This is very helpful. But what I was curious about was COMBINING these effects. Like for example, reducing the hue on a picture with a red tint applied to it. Would one do that by concatenating the two matrices/ arrays used to represent them?

  5. YopSolo

    there is a builtin class in fl.motion named AdjustColor

    the big advantage is that you can use the same value in the flash IDE and obtain the same result with pure AS3

    import fl.motion.AdjustColor;

    _color = new AdjustColor();
    _color.hue = 0;
    _color.contrast = 0;
    _color.brightness = 22;
    _color.saturation = 67;
    _colorMTX = new ColorMatrixFilter( _color.CalculateFinalFlatArray() );

    cheers !

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  7. sonicoliver

    I noticed the hue in photoshop is wildly different to the hue in flash… do you know why the colours end up so different? what is the calculation behind the flash implementation of hue?

  8. Amarjit


    Can you apply Colormatrix to to a top level SWF ? so it will affect all chldren images etc…

    Or can it only be applied to individual buttons, images objects etc.


  9. Matt

    This is a great post.

    Rehul : You cannot normally concatonate complete matrixes. but normally you can pre-multiply them. (look up matrix multiplication). This should combine the effects (preserving order). I would imagine however there is a place where you can put a series of matrixes and they would pre-multiply.

    Amarjit: Try it.

  10. Pingback: Filters! | Final Project Diary

  11. Renu

    I am using Tweenlite and activated ColorMatrixFilterPlugin to change brightness of a MovieClip. Now I want to get the brightness of a MovieClip in onUpdate function. Can anybody please let me know about this. See below the code I am using:

    var tween = new TweenLite(target_mc, time, {colorMatrixFilter: {brightness:1}, onUpdate:function() {
    trace(“I want brightness here”);


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