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rotoscoping techniques
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Colourisation techniques using the rotoscoping method
- solid layers with coarse colour selection
Points to consider:
- using hue, saturation and brightness to fine-tune the layer colour
- Opacity or grey shade within colour - which is better?
- using simple polygon masks (overlapping) to create complex masks
- recycling masks as subtraction masks
- extremely complex masks - cheat with a luma key
COLOURISATION GUIDE ver 1.2 April 2007
The colourisation guide is now available for public viewing.
| ***NEW!!*** | | After extensive research a number of clear objectives and techniques best to achieve them are apparent. It is clear that with a third-party plugin currently commercially available at a low cost (a colourisation plugin able to select up to 5 colours for each layer using the greyscale to affect the area) photorealisation can be easily achieved. Combine this with a freeware colour picker and the colour hex value can be lifted from existing colour materials. The user simply needs to guess the luminance they need and select the approprate area to obtain a hex code for the colour at that point. These presets can be individually saved by the plugin and recycled. |
| For rotoscoping, a javascript addon called RotAE.jsx is the answer. This has recently been available via a forum. This works by taking the masked area and creating as many track points as there are mask points, and allowing you to manipulate the track points one by one. When completed, the track points update the mask as keyframes with each mask point moved to the track position. A simple piece of code, it is immensely powerful. NB: version 1.1 of this script has now been released which fixes an early bug. |
| Compositing still proves to be a problem in that simple polygon 'add' masks on one layer are the best way of selecting a complex area. The resultant shape then needsto be used as one subtraction mask on other layers that overlap otherwise the colour will bleed in and affect other areas (e.g. iris colour over skin colour). There is still some work to determine how best to manage masks. One school of thought is to put the masks on a black solid layer parented to the clip in question then to precomp this down, so that you onle see the precomp as a layer in the main comp. This is fine until you need to subtract the area from other layers. I still have not found a good way of combining masks. Posts to the Postforum and Adobe Forum areas have so far only produced questions as to why combine masks at all. |
| On the subject of combining masks, the most effective route to this I have found is to have the masks on a solid layer, then to render the solid layer, then use the autotrace tool to create a fresh mask. |
| The luma key debate is still raging - luma keys work poorly with greyscale VT footage as the contrast difference between black and white is low, so you often get unexpected results. Current thinking is to use a copy of the clip as a garbage layer with which you apply and prerender a series of effects to ease the burden for the key, namely increase the levels (therefore the contrast) and use the sharpen tool to define shapes. One example of a problematice piece is a tree against the sky background. The leaves on the tree need to be masked as does the tree itself, but the sky needs to be omitted from the mask. As the tree moves, the pieces of sky can be seen through - some appear and some go. It is too complex to use a series of masks and rotoscope each leaf! |
| Finally - precoming is the wonder of my life - thank God for pre-comping. If we do use the tracker and script then every single frame is tracked. This leads to a resulting mask which is difficult to handle, as each change is only affecting 1/24th - 1/30th second of footage - a lot of re-tweaking if it goes horrible wrong. By precomping the footage o 1/5th or even 1/6th of its size we can in effect track every 5th/6th frame only. This is sufficient to realise the techinque as cost-effective and fool th eye into thinking it is always spot on. |
| So why reveal trade secrets? Why not. To make use of this you need a committed/mad person keen to live their life in front of After Effects, or an army of colourists. Nevertheless, this is still more preferable to the frame by frame approach which is time-consuming. |
| Best regards, Matthew Bennett (Colourist) |
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