For the next few weeks, we will be taught about greenscreen and the best way to remove it by using a nuke. This week’s class is about the bases of greenscreen.
The class started off by explaining to us about RGB and HSV, we all knew what was RGB (red, green and yellow), but HSV was something we were not sure of. The HSV which stands for Hue Saturation Value the scale provides a numerical readout of your image that corresponds to the colour names contained therein. RGB can also tell us about the HSV, its broke into.
R = HUE: Hue means colour
G = Saturation: Saturation pertains to the amount of white light mixed with a hue.
B = Luminance: Luminance is a measure to describe the perceived brightness of a colour
By using the RGB and HSL the keyer node ( AKA Luminance key) crates alpha for an image or a video. The node also has different operations like a red key, green key and blue key. The keyer has a range which is a graph where you can control the range of the area getting affected.
Next, we used a shuffle node to isolate colours, for example, we used only one colour like red in the input and for the output connected to all the other colours but not the alpha. Use merge to minus different colours from each other. Using the same technic we remove an area, by just adding an Add mate node and keeping the value at 1 and adding an invert node. Adding a roto can help to affect only one area. Doing this helps to change the colour of an area and it’s easier to roto.
Nuke has a lot of options when coming to keys like:
IBK Colour and IBK Giamo: IBK stands for Image Based Keyer. It operates with a subtractive or different methodology. It is one of the best keyers in NUKE for getting detail out of fine hair and severely motion-blurred edges.
Chroma Keyer: tends to work better with more evenly lit screens that are more of a saturated colour. NUKE’s chroma keyer is that it takes full advantage of any GPU device you have in your system over the other software.
Key Light: It is a really great keyer overall and does colour spill.
Primatte: This is a 3D keyer. It uses a special algorithm that puts the colours into 3D colour space and creates a 3d geometric shape to select colours from that space.
Ultimatte: keys that are good to get detail and pull shadows and transparency from the same image.
Despill is prose when you remove the green which has reflected on an object. When the object standing in front of the green scene the skin reflects the green colour. We can use IBK or the Keylight to despill.
For homework, we had to add an image by removing the green screen from the video.