The RGB Matrix shield can directly plug on the Arduino board, and hook up with the RGB LED matrix, you can use the Arduino to drive the matrix like the RGBduino/Rainbowduino. The code of RGB Matrix shield is the same as RGBduino.
The RGB Matrix shield can be plug on the Arduino UNO/Duemilanove, so the controller is basis on ATMega 168P/328P, the same as Rainbowduino. This design is to make user easily modify or write the firmware of RGBduino by Arduino IDE. But in order to better drive the RGB matrix and reach their best performance, we use the professional LED driver chip, and this chip comprises shift registers, data latches, 8◊3 channel constant current and 64 x 256 gray level PWM for per color! Each channel provide a maximum current of 60 mA.
Each RGB dot has 160K colors in theory, and itís easy to use the 6bit correction register to calibrate the current error for each color LEDs Ė we donít think that Rainbowduino use an adjustable resistors to calibrate the current error is a good idea, because just 1 lap the resistor change from 0R to1K , you cannot get the exact value you need, but now, you have a 6bit software value to correct it.