Finally started playing around with masking in Gimp (did anyone do a tutorial on this? I searched and didn’t find one). Really this scene from the opening of Blade Runner didn’t need much masking but I’m a perfectionist to a fault and wanted it damn near perfect. Also, 492kb! Stoked about that. A few technical notes I’ve found helpful and you might as well:

• When pulling clips from Youtube, search the name with a comma and the letters “hd” to get the best quality source clips you can. You’d be suprised how much high resolution content is on Youtube to use, saving you time trying to rip the material from a DVD.
• When using Gimp, Go ahead and switch your image to “Indexed” mode by going to Image > Mode > Indexed and play around with some of the settings. Dithering helped me a lot on this image where the gradient of the light being cast was screwing up bad.
• If you hide all but the first and last frame you can turn the top layer on and off to evaluate how the transition is working. Often I start with many more frames than necessary and then selectively hide and unhide layers to find the transition that gets it as smooth as possible.