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Auto-Dev and Dev

Posted: Sun Mar 01, 2020 1:21 pm
by alacant
Hi everyone
Observation only. I've noticed that whilst Auto-Dev controls star size well whilst stretching, Dev doesn't. Is that correct?

Re: Auto-Dev and Dev

Posted: Mon Mar 02, 2020 12:17 am
by admin
Hi Steve,

You're absolutely right (copied and pasted from another thread);
Please note that a manual Develop is a fairly crude tool that was specifically designed to emulate photographic film. For example, it blows out (or 'enhances', depending on whether your like the effect!) stellar profiles in the exact same way film does, while dynamic range allocation is precisely as 'dumb' (or pretty! :) ) as photographic film.
AutoDev on the other hand will solve for a stretch that shows all detail in the RoI as well as possible and should/will yield tight stars.

I walked into an op-shop (thrift store if you're from the US) the other day and spotted this wonderful framed photograph of the Horse Head and Flame Nebula. However, it could tell it was indeed acquired using photographic film, as the stellar profile of Alnitak took up a good quarter of the image, while blacks were much deeper, not showing much faint nebulosity. If you are using the Digital Development slider in Develop in StarTools, this is exactly the look it was meant to emulate - for good or for worse.
AutoDev dispenses entirely with the idea that "one formula" (whether a simple gamma curve, ArcSinH, DDP, etc.) fits all. That's just not the case and is - historically - the reason why people would tinker hours with the crude/manual levels and curves tool - e.g. to "eyeball" a histogram transformation curve that brings out as much detail as possible. AutoDev uses computer vision algorithms to "eyeball" these things for you, in a way that is far more objective (and easier & quicker to use!).

The effect of DDP (as partially used by Develop - the "sharpening" effect of photographic film is not applied) predates even levels & curves, as it was meant specifically to emulate a chemical process where you have very little control.