Variable Radius

Here's a gem: the mysterious "Fade" parameter in the Kraussian blur. Each pixel can blur at its own radius! When you turn OFF "fade" it enables the variable-width blur. Sadly, this concept didn't really make it through to the UI.

If you know After Effects, this effect is called the "Compound Blur" and people love it. However, here it's just a bit hard to get to.

Let's start with an image to show this off.

1. 2. 3. 4.

1. Make a new document, 256x256, filled black. Now select half the document and fill white.

2. Start by making a soft selection - no hard edges. (To do one quickly, just draw a shape with the lasso tool and then feather at about 20 pixels.)

3. Now in the Kraussian Blur filter, use the option menu (the triangle in the Parameters menu) to turn on Fade. Apply at about 36 pixels. This is the typical result of rendering a blur with a soft selection -- full blur, or nothing, or fade in-between.

4. Start again with (2.) This turn off the fade parameter. You'll get an astounding result!

Everywhere your selection is "full" the Kraussian Blur uses the exact blur radius you choose (36 pixels). Everywhere else, it will scale the blur radius towards zero proportionally, until at the edge there is no blurring at all!

You can use arbitrary masks and blur each pixel separately. (I recommend getting to be good friends with Quick Mask.)

Notes: I think there are some bugs that cause the variable width blur to apply as if it's rendering to the preview. At times, I've had to crank the radius way up to get a good result. This one deserves to be fixed.

Wrap

One more feature of this filter: wrap.

If you want to blur a wrapping texture in Photoshop, you'd have to manually change your canvas size, copy the image to a 3x3 grid, and then blur, then crop again.

Or you could check the "wrap" checkbox in KPT's Kraussian Blur.

Use this when you're making seamless textures by hand, so you can blur them and not worry about cloning/retouching the edges later.

Gaussians are relatively smooth filters -- they taper very gently, leaving behind very few hard edges. Lenses, even out-of-focus ones, leave some of the hard edges. This is because they blur with a disc, not a smooth bell-curve like the Gaussian. (To understand why this happens, think of the shape of the lens!)

Camera Optics simulates this effect and is a perfect match for rendering out-of-focus backgrounds and depth-of-field effects.

Everything's straightforward here, except perhaps the "blowout" slider. (Ugh, it should be called "Bloom" but somehow that didn't make it.) When you photograph a very bright light out of focus, it will bloom into adjacent spots of the film, leaving telltale colored discs behind. (Cliche movie intro, out of focus streetlamps, yeah that.)

To simulate this, Camera Optics uses a highlight detector, and lets you dial up the "actual" intensity of those highlights. In other words, it detects the bright regions of the picture (the ones that your film, scanner, camera couldn't quite represent) and makes them even brighter.

Two big differences: First, it's a gaussian in 1-D, not a box blur like Photoshop's. Yes, if you're doing shutter blur, a box is more correct, but Gaussians have a lot of creative uses. Also, the KPT Motion Blur automatically wraps on the edges, which is amazing for seamlss textures.

If you haven't realized it, this is an exposed piece of the spiral blur.

For 2 minutes a pop.

I'd talk straight for two minutes, waiting, while they blurred a 640x480 image. And then, finally...

finally...(sorry, thought it was going to apply already)...

they'd finish, and I could zoom in and show how noisy the result was.

Cropped from a 1280x900 image.

And then I'd run the KPT equivalent, wait about a 5 seconds, and show how it was a better-quality result. It was really fun.

I thought it would be more fun to post some old emails about how this filter came to be, rather than just droning on in here. So in the voyeuristic way that everybody loves to read other people's email, here ya go:

They basically use a "maximum" (Lighten in Photoshop) to apply two blurs on top of each other. For the Gaussian case, it's a 1-D Gaussian. For the Spiral Weave case, it's two spiral blurs that have opposite angles (they add up to 90 or 180 or something.) You can make really cool effects with this thing, but there's not a lot of depth to talk about!