Question / Help Chroma Key Vs Colour key

[Kyn Al Nareth]

hi all been using obs for a while now and am looking forward to the 0.12 update.

so heres my question.
what is the difference between the chroma key and colour key filter? do they have different intended uses?

as far i myself am able to tell the only thing seperating the 2 options is a single paramater slider on chroma key "colour spill reduction" but in practice the 2 seem to operate very similarly and share all other capabilitys.

when i try to look this up for clarification i find the chroma key and colour key are used interchangable for the same thing in most descriptions. the only diffirenciation i came across was a single line in one of the may threads i searched through hinting at that chroma key was used for videos or animated source and colour key for static images.

 

[dodgepong]

They are indeed very similar, but the easiest way for me to describe it is that Chroma Key is more for green screens captured by cameras, while Color Key is more for computer graphics.

 

[WilliamBarrows]

I'm not sure if that's actually how they work, but looking at the names the difference is "chroma" vs "color". The difference between chroma and color is that "color" means a full color, while "chroma" is used to refer to *part* of a full color when talking about YUV. Like with RGB, where you have a red, green, and blue component of a color, YUV (the color model used in video for mostly historical reasons) has Luma (the Y) and Chroma (consisting of the two parts U and V). Luma means the greyscale part of a color, and UV is the color part (also know as the "hue" of a color IIRC). This image shows Y, U, and V components seperated.

In other words, I'd think "color" looks for a complete color (including Luma), and "chroma" does the same but ignoring the Luma component. If I am correct in this assumption, "chroma key" will treat differently bright versions of the same color as the same color, allowing green screens to work even when the lighting isn't perfectly even.

 

[DoAGoldeneye]

That makes a surpising amount of sense! :)

 

[Vubar]

If I can add a little bit supporting William's response - I was using a chroma key to change the opacity of a webcam, and I found that it was doing something weird with some plants on my desk (the only green things in frame). Today I switched it to a color key, and the problem went away, and my opacity change was much more even across the image.

This explanation seems to cover what happened with me perfectly, as I think the opacity was affecting different colours in my cam differently. That's why my plant seemed to be flickering and disappearing, because the green of the leaves was being removed, but not other parts of the colour.