Thanks Pascal, I cc the list if you don't mind. I suspect indeed that LR might have been doing something else (and might still do) that impact the brightness and RGB values. But the base curve in DT have a similar effect, right?
I guess it all comes from the effort to match LR and DT results, which I am not supportive for. Though I understand that one may want to transfer some parameters from LR to DT (tags, keywords, etc.). Thanks for the effort, anyway. It is nice that this option LR->DT exists. Cheers denis Le 11/03/2016 16:02, Pascal Obry a écrit : > 2016-03-11 15:48 GMT+01:00 Denis Testemale <[email protected]>: >> I did a small experiment (worth 2 cents, but still useful to convince >> myself). I took 3 pictures 2EV apart: 200ISO / f8 / 1/10s, 200ISO / f8 / >> 1/40s and 200ISO / f8 / 1/160s, of the same scene lighted with a >> constant light, then for all 3 softwares: >> - imported them in Darktable, Aftershotpro and Rawtherapee (the 3 raw >> converters I have access to and use). > > All of them on GNU/Linux. So same driver, same rendering engine.... > >> - deactivated all parameter (auto blabla, local contrast, highlight >> recovery, etc.) which could modify the luminosity of pixels >> - used only the exposure compensation with 0EV, +2EV and +4EV respectively >> - and finally checked visually (which is subjective and prone to errors) >> and quantitatively by measuring the RGB values with the sampling tool. >> With the 3 softwares, the three images are identical in terms of >> exposure/luminosity/RGB channels . I'm not talking about the noise, >> obviously. This is logical to me (and to you also I guess :-) ) and >> means that the 3 software define the exposure the same way. This was my >> point in previous messages when I said that it is an 'absolute' physical >> value. I can check, but I'm very confident that it is the same for LR. > > But again this is exactly what I did with Lr when I was mapping the > .xmp and the exposure > was not taken into account the same way. Strange as it is, it is the > truth. I would have loved > avoiding all this work by just using the Lr values in dt. The same was > true with exposure. > > I was using Lr on Virtual Box on half screen and dt on the other half > for easy comparisons. > > Note that for exposure the offset is not that large, the mapping is > defined like this: > > lr2dt_t lr2dt_exposure_table[] = { { -5, -4.5 }, { 0, 0 }, { 5, 4.5 } }; > > That is -5 on Lr map to -4.5 on dt. 0 is 0 and 5 is mapped to 4.5 and > the mapping is linear. > > I don't remember all the details, this is a long time ago but IIRC I > was matching the highlights > for the 5 vs 4.5, maybe Lr is always doing some hightligh recovery > that dt does not. > > Regards, > ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
