When changing the appearance of a bitmap image at a pixel level, you first need to get the color values of the pixels contained within the area you wish to manipulate. You use the getPixel() method to read these pixel values.

The getPixel() method retrieves an RGB value from a set of x, y (pixel) coordinates that are passed as a parameter. If any of the pixels that you want to manipulate include transparency (alpha channel) information, you need to use the getPixel32() method. This method also retrieves an RGB value, but unlike with getPixel(), the value returned by getPixel32() contains additional data that represents the alpha channel (transparency) value of the selected pixel.

Alternatively, if you simply want to change the color or transparency of a pixel contained within a bitmap, you can use the setPixel() or setPixel32() method. To set a pixel's color, simply pass in the x, y coordinates and the color value to one of these methods.

The following example uses setPixel() to draw a cross on a green BitmapData background. It then uses getPixel() to retrieve the color value from the pixel at the coordinate 50, 50 and traces the returned value.

import flash.display.Bitmap;
import flash.display.BitmapData;

var myBitmapData:BitmapData = new BitmapData(100, 100, false, 0x009900);

for (var i:uint = 0; i < 100; i++)
{
    var red:uint = 0xFF0000;
    myBitmapData.setPixel(50, i, red);
    myBitmapData.setPixel(i, 50, red);
}

var myBitmapImage:Bitmap = new Bitmap(myBitmapData);
addChild(myBitmapImage);

var pixelValue:uint = myBitmapData.getPixel(50, 50);
trace(pixelValue.toString(16));

If you want to read the value of a group of pixels, as opposed to a single pixel, use the getPixels() method. This method generates a byte array from a rectangular region of pixel data that is passed as a parameter. Each of the elements of the byte array (in other words, the pixel values) are unsigned integers--32-bit, unmultiplied pixel values.

Conversely, to change (or set) the value of a group of pixels, use the setPixels() method. This method expects two parameters (rect and inputByteArray), which are combined to output a rectangular region (rect) of pixel data (inputByteArray).

As data is read (and written) out of the inputByteArray, the ByteArray.readUnsignedInt() method is called for each of the pixels in the array. If, for some reason, the inputByteArray doesn't contain a full rectangle worth of pixel data, the method stops processing the image data at that point.

It's important to remember that, for both getting and setting pixel data, the byte array expects 32-bit alpha, red, green, blue (ARGB) pixel values.

The following example uses the getPixels() and setPixels() methods to copy a group of pixels from one BitmapData object to another:

import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.utils.ByteArray;
import flash.geom.Rectangle;

var bitmapDataObject1:BitmapData = new BitmapData(100, 100, false, 0x006666FF);
var bitmapDataObject2:BitmapData = new BitmapData(100, 100, false, 0x00FF0000);

var rect:Rectangle = new Rectangle(0, 0, 100, 100);
var bytes:ByteArray = bitmapDataObject1.getPixels(rect);

bytes.position = 0;
bitmapDataObject2.setPixels(rect, bytes);

var bitmapImage1:Bitmap = new Bitmap(bitmapDataObject1);
addChild(bitmapImage1);
var bitmapImage2:Bitmap = new Bitmap(bitmapDataObject2);
addChild(bitmapImage2);
bitmapImage2.x = 110;