[ptx] auto fine-tune on large images

[Rich]

auto fine-tune is a nice tool, but on large images autotuning single 
point can take a lot of time.

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)

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 ?

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
-- 
  Rich