This command is a specialization of the -blur command, one that convolves images only in the height dimension.

-blur_y convolves an image along the y axis, preserving details along the other two axes. The -display of a 100,100,100,1 volumetric star field, depicted on the left, illustrates the effect. Stars are blurred in the X-Y plane and Y-Z elevation, but remain sharp in the X-Z elevation, where blur_y has no effect whatsoever.

The format of the command is:

-blur_y amplitude[%]>=0,_boundary={ 0=dirichlet | 1=neumann }

Garry Osgood