im_vips2mask(3)
returns a DOUBLEMASK of name out_name containing the data from IMAGE in.
Images must have either one band, a width of 1, or a height of 1.
Returns NULL on error, and a new mask on success.
The scale field is set to 1.0 and the offset to 0.0.
im_mask2vips(3)
writes the doubles held in mask in to the IMAGE out. It creates a one-band
image of the same size as in. It returns 0 on success and -1 on error. The
scale and offset fields are ignored.