When we watching TV programs and some movies some times we amazed by seeing the background of the presenter. Some times in front of a fantasy location or with various moving objects etc.
Technology behind this magic is called chroma keying. In chroma keying uses a special kind of back screen which reflects the light to the direction which to the screen. In the camera side as in the picture, around its opening green or blue colour LEDs were set as a light source. Selecting this blue or green colour is due to a special reason that is they are the less related colours to the human complexion. Most of the time this colours are selected as Green (0,255,0) and Blue (0,0,255) in 8-bit RGB colour pallet.
During the recording all the background is replaced with the source colour due to the direct reflexion of the back screen. In chroma keying filter it removes all Green or Blue pixels as set in chroma level and replaces all them by the feeded frame that is a still image or a video.
In simple mathematic brief in chroma filtering can be described as follows, note that this is not exactly happens in the filter but only for understanding its behaviour.
Let the camera input as ‘C’, Chroma level colour as ‘t’ , provided back image as ‘f’ and the output frame as ‘I’.
Then we can easily generate the resulting frame by masking ‘f’ by ‘M’ with adding the masked image of ‘C’ by ‘~M’.
This algorithm you can simply implement on MATLAB.
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I am Thilina Sameera from Sri Lanka. I completed my undergraduate studies on Electronic and Telecommunication Engineering in University of Moratuwa and currently doing my post graduate studies on Computer Vision and Processor Design at the Department of Electronic and Telecommunication Engineering, University of Moratuwa. I am working as a Biomedical Research Engineer at “Premium International – University of Moratuwa, Research and Development Laboratory for Biomedical Technologies” at the Department of Electronic and Telecommunication Engineering, University of Moratuwa.
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