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Wednesday, December 05, 2007

Comparisons

When you go to an eye doctor he asks you to compare two different lens choices. “Is this better or this better?” Step by step he refines the specific lenses that you need. The visual effects artist goes through similar comparisons to arrive at the final shot. They compare their shot to real references, they compare the shot to surrounding shots and they compare of changes while they work on a shot.

If you don’t have any reference to compare you may drift off course and end up with something that doesn’t work

Real References
During each step in the process the VFX artist should be comparing their work with any real references from the original shoot or research references (stills, video). What needs to be done to match this reference? Does the creature move like the real creature reference? Does the lighting match reference photos?

Sequences
You also want to be able to reference your shot in comparison to others in the sequence. Cut the shot into the sequence and view in context. Does it match the other VFX shots? Does it match the live action shots?

Color
For color balancing, film clips are sometimes filmed out as a wedge. These show a range of color and brightness values and will be used for digital color balance reference. The DP or supervisor may make a selection to use as a guide for a sequence. This is similar to doing color variations in Photoshop. What looks good by itself may not look like the best choice when you can compare it to other variations.

Within the Shot
In the pre-digital days the visual effects artist would create wedges and shoot film tests. These might be checking settings, changes, exposure, and focus or animation tests. It’s still done for miniatures and other photographic effects.

With digital effects you have the advantage of saving multiple versions, undoing/redoing and seeing the results instantly in many cases. The VFX artist takes advantage of this by experimenting and refining. If you add a filter or element you can toggle it on and off to see the result even on a single frame. This would be like the Preview button in the filter dialog within Photoshop or the layer visibility. You also have the option to Undo/Redo to compare any change you just made.

Depending on the software you can load in a previous version or take a snapshot and do the comparison. Some software allows you to do a split-screen to compare 2 versions of an image within one image.

All of this allows the VFX artist to refine their work and make choices.

Changes
When a director or supervisor asks for changes it’s important to make large enough changes so it’s evident looking at the shot. Many artists will make minimal changes and slowly build up to the desired look, take after take. Unfortunately this wastes quite a bit of time. Comparisons are good for you but if it’s not possible for the director to tell the difference without seeing them side by side then it’s not a large enough change.

It’s best to make large steps, which ideally includes going too far. If you had to blur something instead of going by single pixel increments for ten images, it would be better to go by 10 pixel increments. By coming up with an image that goes too far (this could be color, speed of animation. filter, etc), it will allow you to know the range to work in and get a better idea of what the director wants.

A typical phrase in VFX is to “split the difference”. (ILM even had a comic poster of this). This is likely when you’ve gone too far but the previous version or another test didn’t go far enough. In this case split the difference is a way of balancing those two. From that result you might need to split the difference yet again. This is actually a fast way to hone in on the desired look and uses the same algorithm as some computer sorting routines. As you proceed with these adjustments you’ll be comparing the previous versions. If you get to the point where you can’t see the difference without doing a split then you’ve hit the point of diminishing returns.

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