30 January 2012 Previous

Angel on the Battlefield

I hadn't been sitting down long when my phone ran.  It was Rainer Leimeroth, someone I was expecting.  The December holidays were nearing an end and everyone was starting to pick up where they had left off.  We had planned to spend two to three months working on his latest piece, 'Angel on the Battlefield' - an ad he'd done for Annie's Wardrobe.

The shoot and edit had been completed, and all that was left was the post production, which is where I was to come in.  We had been given lessons in After Effects the previous year by James Hall, and I was dying to get my hands on a project to apply what we had learnt.

"I can meet you tomorrow, around three if that's alright." I said, "There are some cool effects to show you."

View the video here


When we met he handed me the final edit.  A letterboxed, somewhat low-res video file shot on a handheld cam.  There were a few luminescent green markers placed on set to help  with tracking, and the sunny sky with Cape Town in the background would need to be replaced.  In their place we were to put a desert-scape warzone where the skies had been ridden black from fire strickerainn buildings and sabbotage.  The guys from Pyranha Stunts had done a fantastic job, I was looking forward to it.


I spent the first few days cutting the video back down into its shots.  It wasn't the most optimal way to do it, but it was the only resource I had.  Some of the shots were continuous, and had been cut up and juxtaposed next to others.  The biggest task was to rename them and their starting and ending frame numbers, both local to the shot and the piece as a whole.

After this was complete, I began creating comps in After Effects.  Slowly importing and prepping each shot for compositing.  During this process I was identifying which shots to begin with to warm up.  The tracking was to be done first, that way I could create static masks to fit the backgrounds for replacement, more accurately place VFX elements to see their behaviour, and mask out moving objects.


tracking_points tracking_points_02

The tracking, however, wasn't that easy.  I wasn't accustomed to the nitty gritty details of After Effect's tracking, and I hadn't yet thought of using Voodoo.  I have since re-worked a shot using Voodoo and Blender, and will complete it soon.  I found Voodoo worked beautifully and would have made life much easier.   In some shots the tracking points became lost off screen, and others were lost due to motion blur from all the action.  In future I wouldn't mind being on set to prep the shots for VFX integration as I think this would be quite fun.  I would try out a couple of things:

  • Where possible, lock the camera down and do camera movements in post
  • Shoot a plate of the frame for a good quality background that could be enhanced
  • Place tracking points in more strategic places to accommodate depth - like put two or three balls on sticks in the distance where a tank is supposed to be, which would cover location and rotation for that element, and one in the foreground for the tracking of foreground elements
  • Place a green screen behind actors when objects like tanks have to appear - so they don't have to be hand keyed
  • And lastly, use the raw footage from the shoot and not the letterboxed video file.  This would be less compressed and possibly more give lee-way for set extension.

A lot of the tracking had to be done by hand at a frame-by-frame level.  It  took nearly two weeks, and when done I began with an even greater task - masking.


hand infront_of_tank_01 helicopter

The skies needed replacement, and because they're 'static shapes' it was decided to tackle them first.  One would scrub to a frame which showed the largest horizon region and draw a mask, then parent it to the tracking object and it would stick.  The mask was noticeably sharp on the skyline and so it was given a small feather value to blend in.

The keying process was then much easier and made me feel like an animator again, keeping me happy.The actors then needed attention.  Sometimes they overlapped with the sky mask and had to be brought back, sometimes elements were placed behind them and they needed to occlude it, like an explosion, smoke or tank - these were the toughest.  The shot where Nurse kneels down to help Soldier with the tank in the background was the toughest.  There's a tank and smoke comped in behind them, and her hands, fingers and hair move over these elements.

Generally, though, they were either walking, running or shooting.  In these cases I applied a technique which James Hall tought us - to break the character up like you would in a rig or puppet, at the limbs.  Five masks were created in these cases:

  1. Torso and Head
  2. Left Arm
  3. Right Arm
  4. Left Leg
  5. Right Leg

Which were all given colour values to differentiate them.  Blue for left and Red for right.  The keying process was then much easier and made me feel like an animator again, keeping me happy. You could then approach it like animating a character, first blocking in the key poses, then breakdown poses and the splines would do most of the work.   If there were props, they would also have their own 'object' mask.

This stage probably took up 50 - 60% of the time, during which most of the VFX elements were placed in as well.  This helped localise only where masks needed to be, and helped 'test' the accuracy of the mask.

VFX Elements

opening_shot tank_02 shadow_01

While the masking was being done, Rainer was sourcing elements to be used.  The project didn't have the time budget to create all the effects from scratch, which saved a lot of work for me.  The tank and helicopter had been downloaded off the web - I don't know where it came from otherwise credit would be given.  We just slapped on a generic, Camoflage, image texture.

The explosions and bullet shots came from Video Copilot's Action Essentials series, and were a pleasure to use.  I didn't have to dig very deep in order to pull off what we needed.  Thanks Andrew.

I used GIMP with some

Once they were added to the shot, i'd tweak the brightness, contrast and colour balance to integrate the element.  Making sure they're fixed to the set is absolutely crucial.


rope_02 rope_01

Keeping consistency between shots was challenging.  In a specific region of a shot the sunlight would be very hot, but later falls in shadow.  This was happened as shoot the day had progressed.  Rainer had sourced image styles to mimick, which were mostly high-contrast, sepia in colour - much like any 'Action Packed' genre.

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