Post Production

Classic Course: Channel Blur

Blurring an individual color channel can be useful both for corrective and creative effects.

To wrap up our exploration of ChOp (Channel Operation) effects, we’re going to look at a fun one that we touched on earlier in this series-within-a-series: Channel Blur.

This effect allows you to blur individual color channels, or the alpha channel. You can use Channel Blur creatively to soften the edges of an alpha channel, or to introduce “chromatic aberration” effects where it looks like the video was shot through a cheap plastic lens (such as the HolgaDiana, and Lomo cameras some creative photographers like to play with – us included). An interesting side effect of blurring a specific color channel such as green is that its complimentary color (in this case, magenta) will also appear:

However, this technique can also be used for a number of corrective actions, such as cleaning up artifacts in highly compressed image formats (such as old DV videos). A particular favorite trick of ours was slightly blurring the green or blue channel when doing greenscreen or bluescreen work (respectively) to remove noise in the background without having to over-crank your keying controls, potentially losing detail across all color channels (such those with the subject’s hair) in the process:

We’ll be taking a break during “NAB month” (April), and will return in May with more movies!

These movies previously appeared in our Insight Into Effects course on Learning. They’ve retired that course from their library, so we’re making them available publicly for free.

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Chris & Trish Meyer founded Crish Design (formerly known as CyberMotion) in the very earliest days of the desktop motion graphics industry. Their design and animation work has appeared on shows and promos for CBS,…

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