How to convert grayscale intensity input to something like the following image?
It seems that no response (0, black) is converted to dark blue, then it goes through other colors to red.
How are these colors derived? Is there any standard gray-to-RGB conversion function for these?
I have tried representing intensity as hue in CIE-LCH model and then converting to RGB through CIE-Lab. But the result weren't as nice as these MRI and PET scans.
Another approach may be a rainbow, i.e. going from high frequency (violet-blue) to lower frequencies (dark red). But is there a conversion formula for this?