2012-05-25

stretching images for human viewing

What I call the "stretch"—the relationship between the data numbers in a data image and the byte values in a human-viewable JPEG or PNG file—is a constant problem for us, in The Thresher, in the Atlas, in the Tractor, and in Marshall's new Lens Zoo project. I spent time today with Foreman-Mackey writing hacky but very robust code for doing this on the fly on the in-progress status plots in The Thresher. The code is ugly! The problem is that you want to see the range of the data but you also want to see the noise level; at the same time, you don't know the noise level in advance and you can hit images (think clipped or sparse images) where it is quite hard to even determine the noise level. Foreman-Mackey and I solved this problem by making multiple noise estimates and using relationships among them to find the best one.

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