OpenCV can't convert to HSI colour?

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I'm required to develop a computer vision algorithm that works in Hue Saturation Intensity colour space, however OpenCV only seems to support HSL and HSV.

Unless OpenCV has mislabelled HSV as HSI or something similar from what I can see of the documentation it doesn't support it (there is no CV_RGB2HSI or equivalent enum).

Am I correct in thinking that you can't convert to HSI using cvtColor and I'll have to implement my own function?