Seeking suggestions on Difference Mask

[sillyman]

To get my footage I've set the shutter then locked the exposure, even set to manual focus. The camera is completely static and the lighting hasn't changed. But for the life of me, doing a clean key with a difference mask is next to impossible. I'm using Vegas with the technique shown in the VASST tutorials. If you've got some hints on how to do a good mask with the HV20 please help a guy out. Thanks!

[24Peter]

You must be doing something wrong. I've gotten very good keys in using ambient light and the chroma key effect in Vegas 7. Are you using this tutorial? http://www.sundancemediagroup.com/articles/chromablur_by_kolbo.htm
(There's also one using the Secondary Color Corrector to create a mask but that's not as good IMO if you have a good background.)
There's no reason to lock focus or even exposure to create good chroma keys. The key to good keys is an evenly lit background and subjects without any background spill on them.

[sillyman]

Hi Peter! I'm not using chroma key due to circumstances (adhoc shooting) so I'm forced to use a difference mask.
e.g. http://www.sundancemediagroup.com/articles/dayvids/difference_masking_in_sony_vegas.htm
http://matthew.chaboud.com/vegas5/twocats/

The lighting is usually whatever is available but its well lit and I avoid shadows. Typical shots are a static wall and a person in front of it (outdoors). Or an office cubicle (maybe the flourescent is trouble?) with lots of overhead light. I've had some limited success by tweaking levels and color curves prior to applying the difference mask and a large helping of bezier masks but it only lasts a few seconds.

[Worley]

I've tried using this method, but I couldn't get very good results. Aside from taking absolute ages to render, it is virtually impossible to get a clean key/mask.

Notice that both the example have relatively uniform backgrounds. This makes it easier to produce good results. But the busier the background, the harder it is to produce good results.

[24Peter]

I've had some limited success by tweaking levels and color curves prior to applying the difference mask and a large helping of bezier masks but it only lasts a few seconds.

Well I think you're asking a lot of any software. As Worley said, uniform colors are needed for any color-based masking. You might try multiple color masks on different layers in Vegas. Otherwise, Bezier is the only other way to go I think

[Worley]

Speaking as one who has taught video editing (and photo editing), any tutorial will use especially chosen footage to demonstrate a task. The footage will be chosen to make the task appear easy. The finished result in the tutorial will look almost perfect, leaving you, the pupil, brimming with the confidence to try it yourself.

And then you realise that things aren't quite as simple...