intensity vs flux bug

I spent some quality time with Ekta Patel tracking down a bug in our visualization of output from The Tractor. In the end it turned out to be a think-o (as many hard-to-find bugs are) in which I had put in some calibration information as if it calibrated flux, when in fact it calibrates intensity. The flux vs intensity issues have got me many times previously, so I might learn it some day. As my loyal reader knows (from this and this, for example) I feel very strongly that an astronomical image is a measure of intensity not flux! If you don't know what I mean by that, probably it doesn't matter, but the key idea is that intensity is the thing that is preserved by transparent optics; it is the fundamental quantity.

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