-blur_y

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 }

• amplitude: sets the spread of the Gaussian distribution kernel, informally the amount of blurring.  One must supply this value; there is no default.
• _boundary: chooses how to handle image edges; see "Pictures have Edges. Now What?" A zero flag (0, Dirichlet) assumes that off-image pixels are black. A unit flag (1, Neumann) assumes that off-image pixels have the exact same value as the nearest edge pixel. Neumann does not exhibit a black vignette, but sometimes edge values become uncommonly bright. This value may be omitted and when it is, the command uses the Neumann policy as a default.

Garry Osgood