Vignetting Correction in RawTherapee

Started 5 days ago | Discussions thread
OP Alen K Regular Member • Posts: 316
Re: Test Your "Flats"

tradesmith45 wrote:

Should have mentioned a couple more things.

First is its a really good idea to test any flat you create by giving it a hard stretch so it shows any illumination "lumps" or artifacts in your methodology. For example fabric over a computer monitor can easily yield banding.

So far my most successful way of making a crude flat to find good adjustment values w/ WA lenses for LR & RT has been to cover the lens w/ 2 layers of fabric & place it a small distance from a completely white display on my computer monitor. But fabric texture will quickly start to show on stopping down. These interfere w/ measuring values from center to corner. Here's examples w/ stretching @ f1.4 & f2 for the Fuji XF16.



As you can easily see, this isn't working too well. Even so, these are still usable for getting much better values for use in LR & RT devignetting adjustments than can be achieved just eyeballing a night sky image.

Other limitations occur with the tiny Lenstip jpg downloaded files. Compression artifacts can quickly show up. These are more problematic than fabric/monitor unevenness.

Lenstip XF16 f1.4

I've bought a sheet of translucent white plastic to try as a better diffuser over the monitor but haven't tested it yet. Have various sky shots w/ fabric & those are same as using the monitor.

I think it's a great idea to use these problematical flats to model the vignetting correction in RawTherapee, which should almost always give a cleaner result. But it's also good to know how to make better real flats for situations where a modelled flat isn't accurate enough or other things need to be corrected as well (such as mirror box shadowing and dust motes). Thanks again for the tips.

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