Hi, Alpha channel works exactly like the gradient, but instead of controling color, you control opacity. You can try the following experiment : - Take any two layer image. - Set an all black gradient for the bottom layer. - For the upper layer, set the merge mode to normal 100% and build a gradient with two control points, one red, the other one blue, for instance. - Open the alpha channel dialog, and set two control points at the same location where you set the ones in the gradient. - Now if you set to 0 the opacity of the alpha channel point that correspond to the blue point, the image should looks mainly red and black, and vice versae. Samuel