The GetLayer command extracts and returns a single layer from a multi-layer image.

The img parameter is the image from which the layer is extracted; it must be of type ColorImage or ColorAImage.

The layer parameter is the index of the layer to extract. For a ColorImage it is an integer from 1 to 3, for a ColorAImage it is an integer from 1 to 4.

output = Image

Specifies a data structure into which the output is written. This can be used to avoid allocating memory. The size and number of layers must match that of the input. The dimensions of the output image are adjusted so that the row and column indices match the input. The default is NULL.