st_makeemptyraster(integer, integer, double precision, double precision, double precision)

args: width, height, upperleftx, upperlefty, pixelsize - Returns an empty raster (having no bands) of given dimensions (width & height), upperleft X and Y, pixel size and rotation (scalex, scaley, skewx & skewy) and reference system (srid). If a raster is passed in, returns a new raster with the same size, alignment and SRID. If srid is left out, the spatial ref is set to unknown (0).