Green Screen & Chroma Key

Green screen technique can be tricky for still or video photographers to master especially if you use DIY or inferior gear. Over the last few years I have read a number of blogs etc about photographers, experience with varying degrees of experience with green or blue screen, lumakey or chromakey techniques.

There are issues which need addressing at the shooting stage of production which will make post-production a less stressful process. The first is the quality of the background, whether you choose to use a painted cyc or cove, or some kind of textile. The colour of the background is critical; what looks green or blue and even to you and the camera in fact may not. This is due to the pigments or dyes used to create the colour. If you go to the local DIY or hardware store and get paint specifically mixed, a number of pigments will be used, not a chromatically specific pigment. The same applies to textiles; what looks green or blue may actually contain contaminates invisible to the mark human eye and video camera. Also, with textiles they must be stretched smooth as any creases create shadows. It's only when you get into post do any deficiencies show.

The other element is good lighting. Remember to ensure that the foreground lighting doesn't contaminate the background. Control it carefully with flags, scrims, barn doors or whatever. Turn of the background lights and check on screen for any spill contamination on the background. Lighting the background is just as important. Make sure illumination is flat and even across the cyc, cove or textile. Make sure you either a native diffuse light source, or hard lights which are diffused in order that any overlap between lights blends evenly and doesn't create hot spots.

My friends at Rosco have created an excellent blog showing green screen best practice, to coincide with St Patrick's Day on 17th March. The blog shows how to shoot the background plate, tips for matching the location lighting in the studio and post-production, including comparing DIY paint issues and the effect of single pigment specific green screen paint.

If you can't read this now, bookmark and read when you get time or refer back when necessary, you will not be disappointed!


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