Ok to clarify: You run two instances of exposure module, or graduated density filter module or CAB module or whichever of the tools is your preference for adjusting exposure. Two instances are used so that you can have one set up optimised for adjusting the sky exposure and the other optimised for adjusting the land. Plainly if your land bit is correctly exposed you will only need one instance for the sky however that isn't particularly good technique as you are always likely to end up with burnt out skies that way , it is better to compromise when originally taking the image so as to have the sky a bit overexposed and the land a bit underexposed.
For the instance processing your sky part you use a drawn mask to only include the sky and not the land. For the instance processing your land part you use a drawn mask to include only the land and not the sky. In practice you can save yourself some time by using the same drawn mask in both instances with the mask inverted in one. If you find there are land features intruding into the sky area that are getting unwanted sky processing and looking odd you can adjust the drawn mask to be more accurate. If the features are so fine this is impractical you can use for the sky processing a combination of the drawn mask and a parametric mask. The parametric mask can then apply whatever type of filtering prevents the unwanted boundary effects - an obvious option being to set that sky processing parametric mask to not work on darker pixels such as those that belong to land areas but the parametric mask offers lots of other options which might suite individual images better. There's a good article from Ulrich on the parametric masks which you can find on the website's blog section although you have to go back to some of the earlier articles for it. -----Original Message----- From: Teodor Petrov [mailto:[email protected]] Sent: 11 June 2014 22:29 To: [email protected] Subject: Re: [Darktable-users] Automatic curve fitting for exposure masking? On 06/05/2014 11:45 AM, Rob Z. Smith wrote: > Have you tried this Teodor? > > a) Activate an instance of exposure IOP (or gradient) with a drawn mask > selecting the sky area. Set your exposure to -1 or whatever it needs for the > sky. Set the parametric mask to work on input values and with it exclude the > darker ranges so that mountain areas present in the drawn mask get affected > less. > b) Create a second instance of exposure IOP with the same mask and invert so > a to select the non-sky area only. Increase exposure as required (I am > assuming you have originally underexposed the shot so as to retain detail in > the sky). Use the parametric mask in input value mode to reduce its effect > on any brighter sky areas that have crept into the mask. Thank you for the suggested work-flow, but I'm not sure I get the idea. Can you show an example? I'm using full scene weighted metering mode when shooting, so on most shots the sky is overexposed and the land is correctly exposed (or close to it). I'm not sure if your proposal can be used in this case. I can share a random raw file that I'm struggling to develop when using a parametric mask, so experienced users of DT can show their skill. :) Best regards, Teodor ------------------------------------------------------------------------------ HPCC Systems Open Source Big Data Platform from LexisNexis Risk Solutions Find What Matters Most in Your Big Data with HPCC Systems Open Source. Fast. Scalable. Simple. Ideal for Dirty Data. 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