Blue screen vs green screen
Both key out fine in this tool. The difference is not in the software — it is in what the two colours do to your subject, to your lights and to your camera. Here is the honest split, with the measurements behind it.
The short answer
Shoot on green unless you have a specific reason not to. Green is the default because a green backdrop puts more light into the channel a digital sensor is most sensitive to, and because green sits further from human skin tone than blue does — a green spill is easier to separate from a face than a blue one.
Pick blue when the subject is warm: skin, brown hair, wood, warm clothing. Green spill on skin reads as sickly; blue spill is easier to live with. Blue also suits night scenes, because it is closer to the ambient colour of a night look and the composite sits better before you grade it. And pick blue when the talent is wearing green, or when foliage is in shot.
Do not pick blue when the talent is wearing blue, when you want to keep a blue sky in frame, or when you are short on light. That last one is the one people get wrong.
The luminance gap is the real difference
Colour separation is not the hard part. In our own preset table, the green screen preset #00b140 carries a chroma magnitude of 83.66 and the blue screen preset #0047bb carries 83.16 — nearly identical. The two colours are equally far from neutral.
Their luminance is not identical. The green preset sits at luma 111.20; the blue preset sits at 62.99, about 57% as bright. On the broadcast presets the gap is wider: #00ff00 at 149.69 against #0000ff at 29.07.
What that means on set: with the same lights and the same exposure, a blue backdrop lands much lower in your camera's range than a green one. Lower means closer to the noise floor, and a key that has to separate a colour from sensor noise is a key that speckles along the edges. If you shoot blue, budget more light for the backdrop than you would for green.
Why most green screen tools cannot key blue
A large number of "green screen remover" tools never measure colour distance at all. They use a shortcut: if the green channel is the largest channel in a pixel, that pixel is backdrop. It works on green and it fails on everything else.
We measured how hard it fails. On our synthetic fixtures, that green-dominance heuristic scores an IoU of 1.000 on a flat green fixture and 1.000 on a shadowed green one — and 0.000 on a flat blue fixture, even when you hand it the best possible threshold. It keys nothing whatsoever. It scores 0.000 on a neutral white wall too.
The key in this tool measures distance in the Cb/Cr plane from whatever key colour you give it, so blue is not a special case. On the flat-blue fixture it scores 1.000 at the shipped default tolerance of 25, and auto-detection reads the backdrop as #0047bb with a maximum channel delta of 0.
Blue tolerates a wider tolerance — on our fixture
One result we did not expect. In the tolerance sweep, the flat-green fixture holds an IoU of 1.000 up to tolerance 85, then collapses at 90: false positives jump to all 21,341 subject pixels and IoU drops to 0.722. The flat-blue fixture, with the same subject, holds 1.000 all the way to tolerance 100.
The likely reason is mundane: on this fixture the subject sits closer to green in the Cb/Cr plane than to blue, so there is more room to open the blue tolerance before it starts eating the subject. Treat it as a property of these fixtures, not a rule. It is one synthetic subject at 320x240, not a survey of real footage.
How to switch this tool to blue
- Open the tool and drop your file in — photo or video.
- Under Key colour, pick Blue. Auto-detect usually finds it; setting it by hand is the fallback.
- Leave tolerance at the default and read the result on the checkerboard. Raise it only if patches of blue survive.
- Export a transparent PNG, a ZIP of PNG frames, or a transparent WebM.
No upload, no account, no watermark. The file stays on your machine the whole time — see why that matters.
When this does not work
- Blue in the subject. A blue key is colour-blind. Blue eyes go transparent. So do blue jeans, a blue logo on a shirt, and a blue phone screen.
- Blue you wanted to keep. Sky, water, a blue LED. Same failure, but you notice it after the export.
- Under-lit blue. This is the big one. Because the blue preset sits at roughly half the luminance of green, a dimly lit blue screen gives the key far less signal. Light the backdrop properly or shoot green.
- Semi-transparent things. Smoke, glass, motion blur, flyaway hair. No chroma key recovers these cleanly and ours is no exception.
- A wrinkled or uneven backdrop. Every fold is a gradient the key has to chase. See the lighting guide.
- Heavily compressed footage. 4:2:0 chroma subsampling throws away exactly the colour resolution the key depends on.
- A single global threshold cannot save every frame. The benchmark page shows the two fixtures where it fails outright.
What we did not measure
We measured brightness falloff on green only: at tolerance 25 a green backdrop down to 0.65 relative brightness still keys out, and 0.60 flips it back to solid. We did not run the equivalent sweep on blue, so we are not going to tell you where blue falls over — we do not know.
Every fixture here is a synthetic 320x240 image, not real footage. The generator, the benchmark and every CSV referenced on this page are in the public repository on GitHub, and the write-up is published on Zenodo under DOI 10.5281/zenodo.22916767.