Photometric color calibration as an alternative model in star color calibration tool

It would be a large piece of programming to build a photometric calibration tool (like the one in The Astro Software That Dare Not Speak Its Name), but boy, would it be nice to have.

But this might be a way to implement it in APP without enormous investment.

Plate solving and photometric catalog lookup are long-since-solved problems. So for some set of stars in the image, we can know what color they're supposed to be without breaking new ground for software development. Adjusting the image so they match seems like a thornier problem.

But since we already have a mechanism for adjusting star color in the calibration tool, we can let the user do the hard part. What if instead of plotting a population of several hundred stars, we plotted a dozen -- twice? The catalog colors can be plotted in one dot color, and the image colors in another. Use the existing sliders to make the two populations coincide, bingo, calibrated. They don't have to exactly coincide, a "best fit" of the sort humans are good at (and computers, not so much) would likely be quite a good start for further tweaking, say in the HSL tool.