[ptx] autopano settings

[Sebastian Nowozin]

Hi everybody,


Lars Schimmer wrote:

>>Just curious what others do:
>>1) How many control points to you try to create per image? I'm been trying to 
>>use unlimited, but I'm not sure if that makes things better or worse.

> Mostly I set it up to 20-30 points/pair. Works fine til yet.
> I think more points are not really useful, as there are limited
> available points at all.

Personally I use 16 points per image, but it depends a lot on the input 
pictures.  For indoor panoramas a large number of points can be 
beneficial as they are spread over the whole picture.  If you go for too 
many points for pictures that only have details in some part of the 
picture (say, a typical outdoor picture with an empty blue sky but a 
textured ground), you get a bias when optimizing for control points that 
are clustered.

   Maybe in a future version of autopano-sift I will implement a smart 
control point pruning that uses a distance map between the points to 
balance the points as much as possible over the images.  So far it works 
like this:
   1) a picture pair has a number of control points (maybe 200 or so),
   2) the control points are removed one by one, maximizing for the area 
enclosed by them,
   3) until the required number of points is reached.

Smarter would be to maximize for some other criteria, lets say the "sum 
of distances from each pixel to the nearest control point" (which equals 
to the double integral of the distance map function), with the 
additional constraint that the desired number of control points must be 
kept.


>>2) Do you do "automatic alignment of images"? Do you tell it to create any 
>>horizontal control lines?

> Mostly yes.

This depends on how much care you take when taking the pictures.  If you 
concentrate on the order of the pictures (strict left-to-right or 
right-to-left) and on always putting the horizon in the middle of the 
picture (easy to do, especially when taking the pictures vertically), 
you can achieve good results with this option and the "add horizon 
lines" one.


>>3) What input size do you use? I've been using 1300 these days, ever since I 
>>upgraded to 1Gig of RAM.

> Input size?
> I use the JPEG Images of my Sony DSC 828 cam, 8 MP and 3x00*2x00 pixels.
> Far big, but OK if you don't use more than 20 pics in a panorama :-)
> And RAM, 1 GB is not much ;-)

1300 is a good default for 512Mb RAM, 700 for less RAM.


>>4) Do you use the refinement step?

Only if you want the maximum quality this makes sense.  I usually 
disable it, because it slows the program down to like 20% of the 
original performance.


Regards,
Sebastian

PS: (I know I said this before), but in the next two weeks there will be 
a new version of autopano-sift with some small fixes and maybe the 
improved control point pruning.