[jffry]

Another opportunity for efficient blur would be to rescale the image if the blur radius is above a certain amount. This incurs overhead, so for smaller radii it might be more efficient to just blur the full-size image, but for larger radii you can first reduce the image, blur with a smaller radius, and then upscale the image.

You might need an Arbitrary Hack Constant (oh, sorry, "tuning parameter") to decide when to make that transition.

[crazygringo]

That's already in the article:

> Instead of filtering the image in its native resolution, I used OpenGL's native support for linear interpolation to downsample the source image by 4X in width and height, blurred that downsampled image, then linearly upsampled via OpenGL afterward.

[jffry]

Indeed it is, my bad for not RTFM