I am doing two runs of enblend: one "high brightness" and one "low brightness" which will be merged together in Photoshop to form a composite. (This is so that clouds are not overexposed and the ground is not underexposed)
It's a large project - it consists of 35 x 16 megapixel images. On my 3.5GHz dual core CPU (Windows XP) it has been going for 17 hours, and it's not even halfway through. At this rate running it twice will take at least 5 days in total!
My question is whether there is any way to run the second pass without redoing all the calculations, since the *detail* is identical; only the overall brightness differs, and it's by a consistent amount for every pixel.
Thanks in advance...
I am afraid this is not possible. The masks could in theory be reused but the image pyramids cannot.
If you are doing a multi-row panorama, I highly recommend blending each row individually, and then combining the complete rows to create the final image. You can apply this technique to the rows as well. For example, blend the left half and right half of each row individually, and then merge them together to complete the row.
Enblend has the best performance when you keep the overlaps well-organized like this. If you use the -a flag, then Enblend will try to blend multiple overlaps at the same time, and this can be slow. I don't recommend it for large projects.
Another important point is to set the value of the -m parameter correctly. This controls how much memory Enblend will use before starting to store intermediate calculations to the hard drive. This parameter should be less than the total RAM you have in your machine by 25% or so (this saves space for Windows itself and a few other programs that you might be running). The default value is 1 GB. If you only have 1 GB of memory, try a smaller value like -m 750.
I did take the pics in two rows. Just a question though, can a front-end like PTAssembler (using Panorama Tools) still properly invoke enblend in this case, or do I need to do it manually? I guess it's better to manually pass the NAMExxx.tif intermediate files that PTAssembler/Panorama Tools has created on the enblend cmdline...
Are there likely to be any quality issues with blending twice over the areas where vertical and horizontal seams cross?
I don't think that PTAssembler has this ability. You need to do it manually. I typically do something like this:
enblend -z -o top.tif a0000.tif a0001.tif ...
enblend -z -o bottom.tif a0010.tif a0011.tif ...
enblend -z -o out.tif top.tif bottom.tif
All of the images from the top row go to the first command and all of the images from the bottom row go to the second command.
There should be no quality issues with this approach.