Forty years ago, BBC Horizon released a documentary called “𝗛𝗼𝘄 𝘁𝗼 𝗙𝗶𝗹𝗺 𝘁𝗵𝗲 𝗜𝗺𝗽𝗼𝘀𝘀𝗶𝗯𝗹𝗲.”
They visited Industrial Light & Magic to show how the magic was made.
In this segment, the illusion isn’t painted or modeled, it’s separated by light.
To place a spaceship over an explosion or a hero over a painting, ILM relied on blue screen compositing.
A precise process of masks and mattes, each one built from the original film, each one aligned to within thousandths of an inch.
One pass exposes the ship.
Another exposes the background.
Together, they merge through the optical printer, frame by frame, until both worlds occupy the same space.
Any shift, any dust, any vibration would reveal itself as a thin black halo, the price of imperfection.
This was the craft before digital compositing:
a choreography of filters, film stock, and patience,
where invisibility was the ultimate proof of skill.
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