Chroma Key: Green vs. Blue | Articles | Photo, video, optics

Green or blue screen back­grounds, also known as chro­makey back­grounds, allow film­mak­ers and pho­tog­ra­phers to eas­i­ly replace the back­ground in a frame with almost any image or video. So, you can place your actors and mod­els on a busy New York street, in a haunt­ed house, or on the sur­face of the moon.

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Both blue and bright green back­grounds are com­mon in Hol­ly­wood, but what is the dif­fer­ence between the two col­ors and how do they work?

Where and how does chroma key work?

In post-pro­duc­tion, chro­ma key makes it easy to replace back­grounds, use CGI and oth­er visu­al effects. A sol­id blue or green back­ground is dig­i­tal­ly replaced with the desired pho­to or video.

It is often used in super­hero, action and adven­ture films. So, for exam­ple, The Avengers was filmed on chro­ma key, and John­ny Depp in Pirates of the Caribbean.

pho­to of Dis­ney Enter­pris­es, Inc.

How­ev­er, the most com­mon exam­ple of chro­makey over­lays are weath­er releas­es. In fact, the hosts are stand­ing in front of a green screen in the stu­dio, and all oth­er images are super­im­posed dur­ing edit­ing.

scripted.video

The most impor­tant thing to remem­ber about chro­ma key tech­nol­o­gy is that its col­or will be dig­i­tal­ly replaced on any sub­ject in the frame.

For exam­ple, if the pre­sen­ter is wear­ing a green dress in front of a green screen, her out­fit will also be dig­i­tal­ly processed in post-pro­cess­ing.

Source: wifizify.com

What to choose: blue or green screen?

Even though blue screens and green screens work in the same way, they are not com­plete­ly inter­change­able. There are cer­tain sit­u­a­tions where one col­or is more prefer­able than anoth­er.

Color brightness

The green used on the chro­ma key is slight­ly brighter than the blue. If you’re shoot­ing night scenes, it’s best to choose a blue screen because there will be less light to bounce around and poten­tial­ly cause prob­lems when shoot­ing. The extra bright­ness on green screens can be use­ful for day­time scenes.

Also, the green glow can lead to col­or blotch­es on some sur­faces and tex­tures, such as blonde hair.

color border

When using any col­or on the screen, you need to pay atten­tion to the col­or fring­ing around the edges of the object.

Many pro­duc­tion design­ers pre­pare for this prob­lem by using mat­te sur­faces to pre­vent blues or greens from reflect­ing, and by prepar­ing all sets, props, and cos­tumes to avoid light reflec­tions.

Blue screens usu­al­ly cause few­er col­or patch­es than green screens. If you’re work­ing on a green screen and often expe­ri­ence fring­ing, try blue chro­ma key.

Digital cameras vs. film cameras

If you’re shoot­ing with a dig­i­tal cam­era, in most cas­es it’s a good idea to use a green screen. The tech­nol­o­gy used in dig­i­tal cam­era sen­sors is bet­ter suit­ed for accu­rate­ly cap­tur­ing green. This is why most mod­ern film pro­duc­tions use green screens.

Skin tones

Both blue and green are ide­al col­ors to use in chro­ma key because they don’t show up in most human skin tones.

How­ev­er, if the sub­jec­t’s skin has a blue or green tint and you notice that you’re hav­ing prob­lems with shad­ow col­or, fring­ing, or reflect­ing the sub­jec­t’s skin tone, you might want to change the back­ground col­or.

Sets, costumes, and other on-screen color sources

If you go to work know­ing that you will be using chro­makey tech­nol­o­gy, you should com­mu­ni­cate your plans to the pro­duc­tion design­ers from the very begin­ning. They will make sure that there are no bright shades of blue or green in the cos­tumes, on the sets and props off the frame.

If you know in advance that the char­ac­ter should have a bright blue suit, use green chro­ma key and vice ver­sa.

Output: green or blue screen

So we will use:

— blue screen when shoot­ing night scenes; in the pres­ence of a large num­ber of objects that reflect light; if you have a hard time fight­ing with the green edg­ing of objects in the frame.

— green screen when shoot­ing day­time scenes when using a dig­i­tal cam­era.

In addi­tion, pay atten­tion to the objects in the frame: if you have green objects in the frame, suits or, for exam­ple, the Hulk, use a blue back­ground. And vice ver­sa.

Folding chromakey: to be or not to be

Also, when choos­ing a chro­ma key, you may encounter anoth­er prob­lem: choose a fold­ing screen or a reg­u­lar, fab­ric one.

Folding chroma key

Pros: does not wrin­kle; easy to trans­port and move due to the fold­ing design; you can do with­out a back­ground instal­la­tion sys­tem by lean­ing it against the wall.

Cons: it will not work to shoot a per­son in full growth.

So, for exam­ple, the fold­able Ray­lab RF-12 on a flex­i­ble frame can be fold­ed into a spe­cial case. Its size in the assem­bled state reach­es only 50 cm. More­over, it com­bines two col­ors at once — both blue and green from dif­fer­ent sides!

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Normal chroma key

Pros: you can shoot more com­plex actions, cap­ture a per­son in full growth.

Cons: Wrin­kles more eas­i­ly, instal­la­tion sys­tem required.

Ray­lab RL-BC01 — back­drop 3 meters long and wide. Made from muslin, it pro­vides strength and dura­bil­i­ty to the fab­ric. The mate­r­i­al absorbs light well and does not give glare. Don’t for­get to pur­chase an instal­la­tion sys­tem for it.

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Thus, if you plan to shoot any objects or a per­son will be waist-deep in the frame, a fold­ing back­ground will be enough for you. For more com­plex shots, where you need to use a per­son in full growth, you will need a more dif­fi­cult-to-use fab­ric chro­ma key.