How to key glass against a green screen

The client wants the bottle on white for the site and on a lifestyle background for the campaign, so someone shot it on green, and now it is your problem. Glass is the worst subject a chroma keyer can be handed, because the glass is doing three things at once: transmitting the screen through its body, tinting that transmission at the edges and curves, and laying specular reflections on top. To a color-distance keyer, most of that bottle simply is green, and the matte comes back with the body of the product missing.

The trap is treating that as a keying failure. The transparency is the product. A real bottle on the new background should show the new background through it.

The honest options

Reshoot on white or black. For pack shots that will only ever sit on a studio background, shooting on the final background is the free fix and the industry default. If the deliverable list is one background, argue for this before touching a keyer.

Rebuild the bottle in comp. The traditional high-end answer: pull what you can, then reconstruct refraction with a displacement of the new background, rebuild speculars from a luma key, and grade the glass tint back in. It produces beautiful results and consumes a day per setup, which is fine on a hero shot and absurd for a 40-SKU product run.

Unmix it. A neural unmixing keyer treats glass as what it is: pixels that are partially foreground. Key Studio Pro predicts, per pixel, the foreground’s own color, the tint and the speculars, and a linear alpha carrying the transparency. Composite the FG over the new background with that alpha and the background shows through the glass at the right strength, with the reflections sitting on top.

Pulling it

1. Run the shot through the app and open the Comp preview. The checkerboard should be visible through the glass body, dimmed by the glass, not absent and not full strength.
2. Composite the passes over the real background in linear.
3. Judge the refraction. The alpha carries transmission strength; it cannot bend the background (more on that below). For most product glass, straight transmission reads correctly. For thick or heavily curved glass, add a subtle displacement in comp.

What the key cannot carry

Refraction. The screen seen through the bottle’s curves was bent and magnified, and an alpha channel is a per-pixel opacity, not an optical model. The unmixed result gives you correct transparency and correct surface color; the new background passes through straight rather than warped. Side-by-side with reality, thick glass will read slightly too calm. Whether anyone who has not seen the real bottle notices is a judgment call, and for e-commerce work the answer is usually no.

Green cast inside the glass is the other watch item: a green screen seen through green-ish glass leaves spill in the transmission. The despill guide applies, gently; over-suppressing kills the glass tint the client paid for.

Common questions

Would blue screen have been better for glass?

Often yes, especially for warm-toned liquids and gold labels, since blue contaminates them less visibly. The app keys either color; the advice matters for the next shoot.

What about liquid in the bottle?

Liquid is tinted transmission, the same physics as the glass, and it unmixes the same way. Carbonation bubbles are tiny speculars and survive in the FG pass.

Reflections of the studio are visible in the glass. Key problem?

No, photography problem. The key faithfully keeps the reflections, including ones of the green screen itself. Flag reflections on set, or paint them in comp.

Same story for smoke, steam, and bottles pouring?

Same story: they are all semi-transparent foregrounds, the case binary tools round away. Why AI roto looks cut out explains the rounding, and the motion side lives in the motion blur guide.