At the core of most of the Blur/Sharpen effects is something called a convolution kernel. It changes the brightness values of pixels using a mathematical formula. What makes each Blur/Sharpen effect unique are the user-supplied variables?the values given to the center pixel and its surrounding pixels within a three-by-three matrix. Once calculated, the formula divides the sum of those pixel values by another user-set variable and then adds yet another user-selected value to that quotient, thus creating the desired effect.
So it's not surprising the Convolution Kernel effect can handle most of the effects in this category. But Adobe's Premiere effects creators recognize that the convolution kernel is not for the faint of heart. So you'll find that it's easier to use some specific Premiere effects rather than the convolution kernel's presets, much less attempt to deal with its variables and calculations.
Anti-alias? You may have tried this in Hour 11. It softens edges between contrasting colors and light.
Channel Blur? This AE effect, illustrated in Figure 12.18, shifts RGB (red, green, or blue) colors individually, creating a blurring effect. It works well with alpha channels, letting you shift the colors of graphics.
Figure 12.18. Channel Blur lets you shift color pixels, creating unique blurring effects.
Convolution Kernel? This is the workhorse of this category. But of its 10 presets shown in Figure 12.19, only Sharpen Edges works better than its single-purpose cousins. Stick to the other recommended Blur/Sharpen effects and experiment with Convolution Kernel to create your own effects.
Blur? Very subtle. Use Directional Blur or Fast Blur instead.
Blur More? Directional Blur and Fast Blur work better.
Emboss? Use the Color Appearance Emboss effect instead. It gives you more control.
Light Emboss? Use Emboss instead.
Find Edges? The After Effects Find Edges effect is a full-featured and powerful tool that identifies and emphasizes areas of an image with obvious transitions/edges. I'll go over it in Hour 13.
Gaussian Blur? This is nearly the same as Fast Blur.
Gaussian Sharpen? This is on par with the non-Convolution Kernel Gaussian Sharpen effect.
Sharpen? The After Effects Sharpen effect has a slider, so it works better.
Sharpen Edges? This is the only Convolution Kernel preset that outshines the specialized effect.
Sharpen More? Use Sharpen instead.
Figure 12.19. The Convolution Kernel Settings dialog box. Changing only one or two values can dramatically alter a clip's appearance.
Directional Blur? By smearing pixels in a user-selected direction, as illustrated in Figure 12.20, this effect supposedly gives the illusion of motion. I don't think it's all that effective, but it is a good way to simply create a blurred image.
Figure 12.20. Directional blur is supposed to give the illusion of motion but does not fulfill that promise.
Fast Blur? This creates a much more blurred image than Directional Blur. Figure 12.21 shows how easy it is to use. Apply keyframes to create an ever-increasing blur over time. This works better than Gaussian Blur or Camera Blur.
Figure 12.21. Fast Blur creates the blurriest images.
Radial Blur? The "Psycho" look. It creates a whirlpool blur that simulates a swirling camera. Figure 12.22 shows that you can vary the location, type, and quality of the blur.
Figure 12.22. Radial Blur gives a video clip a soft swirling look.
Radial Blur is a processor-intensive effect?thus the three Quality settings. At the highest quality, Premiere's Real-time Preview will likely stutter through the clip. Rendering Radial Blur at its full quality takes extra time.
Sharpen? This effect sharpens a soft-focus image by increasing contrast where color changes occur. As Figure 12.23 shows, this effect uses only a single slider. It works better than Gaussian Sharpen or the Convolution Kernel's Sharpen and Sharpen More presets.
Figure 12.23. Sharpen gives soft images a focused look.
Camera Blur? Directional Blur handles this and adds a direction component.
Gaussian Blur? Same as Fast Blur.
Gaussian Sharpen? Convolution Kernel is as good.
Sharpen Edges? Convolution Kernel is as good and has more options.