Blur text one pixel vertically??

[Kevin Camp]

i’d try fast blur constrain the blur to vertical.

i would imagine that they are telling you to do this to mask subpixel movement that is causing ‘wavy’ edges of the text as it moves. this is due to rasterization of the text as travels up the screen.

you can prevent that from happening by restricting the movement of the credits to whole pixels (or even numbered whole pixels if rendering interlaced). the negative side of this is it becomes harder to ‘fit’ a credit roll to a specific duration…

here is a simple expression to create that kind of movement:

offset = 2; // number of pixels to move per frame
y = offset + timeToFrames(time-inPoint);
value – [0,y]

you’d paste this into the position property of the credit text, no key frames needed. just postition the credits where they need to start and they’ll march on up the screen.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[Todd Kopriva]

In addition to Kevin’s tip, there are some tips in the “Best practices for creating text and vector graphics for video” section of After Effects Help about both avoiding and mitigating the problems that come from vertical movement of small details together with interlaced video.

Basically, the problem (well, one of the problems) is that thin elements of text can disappear and reappear as they move across fields, unless you make really certain that the thin elements don’t get hidden by the alternating fields. If you time it exactly wrong, you can make a thin horizontal line disappear entirely; but more likely it will be hidden and shown in a pattern that makes a high-frequency strobing or “sizzling”. Avoiding this involves either math or the application of animation presets (in which someone else has already done the math). There’s an Autoscroll – Vertical animation preset in the Behaviors category.

You can also avoid the problem by just making sure that the thinnest elements aren’t so thin. Blurring something spreads it across more pixels, so a vertical blur is basically just fattening the text up in the important direction. That is exactly what the Reduce Interlace Flicker effect is for. It’s a very specific vertical directional blur.

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Todd Kopriva, Adobe Systems Incorporated
putting the ‘T’ back in ‘RTFM’ : After Effects Help on the Web
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