ImageCompose

• ImageCompose[image, ...] always gives an image with the same pixel size as image.

• ImageCompose[image, obj] does alpha-blending if obj has an alpha channel.

• ImageCompose[image, {obj, }] effectively sets the alpha value for obj to , or multiplies an existing alpha channel by .

• ImageCompose[image, obj] overlays obj pixel-by-pixel onto image, without changing the size of obj.

• The object obj can be either an explicit image object, or a graphics object that is automatically rasterized to have the same image size as image.

• ImageCompose[image, obj] centers obj in image.

• The position pos in image, or the position opos in obj can be specified in the following ways:

• Possible named positions include Top, Bottom, Left, Right, Center.

• If only one of pos_x and pos_y is given, the other is assumed to be Center.

• The pixel offsets {x, y} can be negative, indicating a point outside of image or obj.

• ImageCompose[image, ...] yields an image with an alpha channel only if image has an alpha channel.

• ImageCompose[{image, _i}, ...] effectively adds an alpha channel with value _i to image.

• ImageCompose[..., {f_i, f_o, mode}] combines a fraction f_i of every pixel value in image with a fraction f_o of every pixel value in obj, in all cases taking account of alpha channels.

• With value 1 for mode, obj is treated as on top of image. With value -1 it is treated as underneath. And with value 0, image and obj are treated symmetrically.

• The following choices of {f_i, f_o, mode} correspond to standard Duff-Porter compositing operators:

• The "over" operators given by {1, 1, 1} and {1, 1, -1} effectively perform alpha blending.

• The "in" operators given by {0, 0, 1} and {0, 0, -1} mask one image with the alpha channel of the other image.

• The "out" operators {0, 1, 0} and {1, 0, 0} mask one image with the complement of the alpha channel of the other image.

• The "atop" operators given by {0, 1, 1} and {1, 0, -1} effectively combine the alpha channels of the two images before performing alpha blending.