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Overscan Rendering

Overscan Rendering

There are often times you are setting up the perfect framing, but you need more space around your frame for a variety of reasons.

For example:

  • It is a print piece and you need extra bleed around the edges.
  • You render something that needs integrating into filmed footage and the image needs extra bleed for the lens distortion.
  • You render a wider or higher version of your shot so you can pan across it in comp to save render time.

So you have identified the need to render an overscan version of your shot. How do you make it happen?

It's quite simple really. Simply multiply the resolution and/or the film back by your scaling term.

Variant 1: Overscan with known output resolution

New Film Back Width = Current Film Back Width * New Render Width / Old Render Width
New Film Back Height = Current Film Back Height * New Render Height / Old Render Height

Variant 2: Overscan with known output scaling

New Film Back Width = Current Film Back Width * New Ratio
New Film Back Height = Current Film Back Height * New Ratio
New Render  Width = Current Render Width * New Ratio
New Render Height = Current Render Height * New Ratio

For example if I am rendering a HD shot with a standard 35mm camera and need to add 100px to either side I can simply calculate my new Film Back:

2020px / 1920px * 36mm = 37,875mm

Or if I know I need to add 12% to my width:

1920px * 1.12 = 2150px
36mm * 1.12 = 40.32mm

This will give me an image that is 12% wider but fits pixel perfect on top of my smaller framing (not accounting for tiny rounding errors).

Overscan added to all sides.

Overscan added to all sides.

Take the Tedium Out of It

For people that rather not multiply and divide a bunch of numbers and then select several items and type a bunch of other numbers, I have prepared a simple script that will ask you what your scaling method is and then does the rest for you.

Simply put it in your scripts folder and execute it by calling @bd_overscan.py from modo's System/Evaluate… menu.

Going Smaller Can Be Powerful as Well

So far we have only applied our newfound knowledge to make images bigger by extending the frame. Of course, the inverse also holds also true. You can create a crop of your shot by multiplying your output resolution and film back by numbers smaller then 1.0 as well. This allows you to crop in on a specific detail of the frame. Well, so far it only allows you to crop to the center of the frame.

Offset

To get this trick to work and not simply crop in at the center we need to add two more properties to our workflow: Film Back Offset X and Y

Now say we take the 12% bleed from the above example but we only need it on the right?

We'd still get the same result for the overall widths:

1920px * 1.12 = 2150px
36mm * 1.12 = 40.32mm

But now we need to shift our whole frame to the left to get all of our bleed happening on the right edge of frame. By how much? Simple. The difference between our new and old Film Back Width.

40.32mm - 36mm = 4.32mm

So our new Film Back Offset X needs to be 4.32mm. Voila.

With this new knowledge and a piece of paper you can now adjust the bleed and crop of your renders to your hearts content.

Of course there is a script for that

There always is if the problem is well enough defined. In this case it is an excellent modo plugin called Cropper by Adam O'Hern, which does all the above and much more. I'm a big fan of his work if you can't tell and I highly recommend that you check out his other plugins as well. They are well worth the price of entry.

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