The Difference Between Chroma Key and Luma Key

Chroma Key

Chroma key compositing is a special effect/ / post-production technique for laying two images or video streams together based on the colour hues / chroma range. The technique has been mainly used to remove a background from the subject of a photo or video, in particularly used in the news, weather presenting and video games industries. A certain colour range on the top layer is made transparent, which then reveals the layer underneath. The technique is mainly used in video production and in the post-production stages. The technique is also sometimes referred to as colour keying and other terms such as green screening and blue screening.

When green or blue screening, a subject is placed in front of a green or blue screen that is lit perfectly so that it is all the same shade of the colour, and they as filmed. Then, in the post-production stage, the colour used as the background is taken away, leaving a transparent part on the video, which then reveals the layer behind. A problem with this is that the subject cannot contain as of the colour that will be taken away, otherwise they will also become transparent.

A great example of green screening that everybody will have seen is during weather presenting. The presenter appears to be stood in front of a large map of the country however, they are stood in front of a big green screen and then the map is put onto the screen digitally.

Luma Key

Luma keying is setting the brightness level, so all of the brighter or darker pixels from the set level are turned off, making them transparent. The image or video behind the top later will then be shown through the transparent sections of the top layer. Luma keying is used when working with grayscale images.

Luma keying is very similar to chroma keying, however, the difference is is that is uses the brightness for transparency whereas chroma key uses a colour range.