[ptx] auto fine-tune on large images

[Rich]

note : i first sent this to pablo privately (didn't check reply 
address), now i'm adding some more info, too

Pablo d'Angelo wrote:
> Rich schrieb:
> 
>> auto fine-tune is a nice tool, but on large images autotuning single 
>> point can take a lot of time.
> 
> How large are large images? And how many of them are in your project.

this is a 360 panorama in two rows, totalling 30 images. first i merged
both rows separately (by running enblend on them on a separate machine
at the end - it had more ram and as a result process was much faster)

>> what could be done to speed up this process ?
>>
>> i checked finetune preferences and didn't change any parameters that 
>> were specified in pixels, only reduced 'search area width' (which 
>> didn't help a lot though, and it seems that it is constantly reset 
>> back to 10%)
>> (rotation check is disabled)
> 
> Ok, will check that. It shouldn't pop back to 10%.

it seems that it reverts to 10% after each finetuning, at least for this
pair of images (or maybe even _before_, as i can see no difference in 
performance when changing this quite radically)

>> a big part of this process is some sort of grayscale generation. is 
>> this done for some small region around added control point or for 
>> whole image ? if this is done for a small area, it's extremly slow. if 
>> it's done for a whole image, why is it done every time an auto 
>> finetune is performed ?
> 
> Currently its done for the whole image, but it should be done only once, 
>  and then stored for further use. Also, it shouldn't be terribly slow. 
> By default, hugin uses ~ 80 MB to cache images (both the color images as 
> well as the grayscale images).
> It might help to increase the Image Cache size to something bigger. It 
> can be found in the Preferences on the "Misc" tab.

i'll try this out, though hugin already takes a lot of ram :)

>> finetuning a single point to two images (rows for multirow panorama) 
>> takes approx 15 minutes, so probably a lot of information is parsed 
>> that gives no real benefit, but i could not find a way to reduce this 
>> time
> 
> Hmm, that is strange. How much memory do you have, and how fast is your 
> computer?

unfortunately currently i have access to a computer with only 512mb, so
i can't tell wether additional memory would radically speed this process
up. it's p4-celeron/2.2ghz.
during most of the process heavy swapping takes place and total memory
usage is somewhere between 1.5g and 1.9g.
both pictures are ~15796 wide. vertically they have black areas (alpha
channel ?) - maybe cutting them out in gimp before import in hugin might
help a little ?

oh, this is linux machine with 2.6 series kernel, x.org 6.8.2 and kde 3.4.

> ciao
>   Pablo
-- 
  Rich