Not really a bug, per se, (and not in Dt) The application which is being used to do tho merge is using integer arithmetic. (Dt uses floating point). When an int goes beyond its range, it gets clipped to the maximum. Any correction then gets evenly reduced. So for an integer between 0 and 255, a value of 255 gets increased by 30%, it remains at 255. If reduced by nineteen percent, it becomes 206. The clipped areas in your “bright” image got reduced to an even grey.
With fp values, nothing is really “out of range” (technically possible, but nevermind that), meaning that if the value is to fall somewhere between 0 and 1, but it gets computed to 1.3 (or even 17.9), the variable can still hold the number. If these numbers are then later reduced accordingly, and, if reduced by nineteen percent, is still 1.053, or still at saturation (>=1). So, with the two images, the application does some maths on a certain value near zero, and a certain value at 255, and it results in another value, (somewhere in the vicinity of > 127). But with the tree images, at some point, the high value got clipped, and then reduced, resulting in the even grey circles. One can say, “but I used a 16-bit format.” Sure, but if it was a 16-bit integer format, one still has the same problem, except now, the values are 0-65535, and 65535 times 30% is still 65535, reduced by 19 % is still 53083. With a 16-bit fp, or a 32-bit fp, the answer is still 1.053; the only difference is to what decimal place accuracy. Perhaps, if the images were sent to the algorithm in a different order, it would not have resulted in the clipping. Pipeline order is important, especially with integer mathematics. Talk to the developers of the program doing the merge, to consider using a fp pixel pipeline in their next major upgrade. (That is no easy feat. It may involve a total rewrite, and a few years. Just ask the developers of The GIMP). Sincerely, Karim Hosein Top Rock Photography 754.999.1652 On Tue, 1 Sep 2020 at 15:49, Michael <[email protected]> wrote: > I merged three files of a room and got a round discoloration. I then > merged The lighter and darkest image and the pic was normal. If it is > a bug please fix it. If it isn't a bug nevermind:) > -- > :-)~MIKE~(-: > images > https://drive.google.com/drive/u/2/folders/0B2xvsVTZy4y1ODR6dTk5UldpR3c ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to [email protected]
