[ptx] PTmender: some thoughts on performance

[dmg]

Hi everybody, 

(I am never sure whether to cross-post, specially because I feel that
everybody in the panotools-devel is in the PTX, but on the other hand
I feel that it is important to archive in the panotools-devel list
these discussions).

I just got my Nodal Ninja 3 and I really like it. Of course I had to
try it with a spherical panorama, in this case of my kitchen.

http://turingmachine.org/silvernegative/index.php?/archives/565-Kitchen.html

I know, the picture is imperfect, particularly the nadir. 

What I wanted to comment on are the following issues:


* Each component  image was 8 megapixels, JPG.

* I used hugin (Dec 2005) and PTmender 2.8.3

* With the cropped processing in panotools the time it takes to create
  the component images has been dramatically reduced. The new bottle
  neck is not CPU, in my opinion, but disk throughput. This image was
  created with 19 photos (2 rows of 8 + 3 nadir) and the resulting PSD
  was bigger than 1 gig (and it was only 8 bit-depth). Each cropped
  tiff was forty-something megabytes. It took PTmender around 1 hr.

  Particularly the creation of the PSD. For each component layer the
  following was done:

  * Map image  (creates cropped TIF)
  * Create alpha channel/stitching mask (creates another TIFF)
  * combine alpha channel (creates another TIFF)
  * Create PSD (create a new psd file per layer, as more layers are
    added, the PSD grows, delete previous PSD).

  So one of the main challenges is that the PSD creation is o(n^2)
  --where n is the number of images. If you consider that the average
  size of the PSD was 0.5 gig that is a huge, huge amount of data that
  flows from the disk to the memory and backwards.

  Of course not everybody creates PSDs. If speed is required, then use
  cropped tiffs as output.
  
  So PSD should be considered as a "slow" process in its current
  implementation. if anybody is looking for something to do, this will
  be a fun project to work on.

* Vignetting. Given that I am still using hugin from last December, I
  can't fix vignetting in hugin yet.

* Feathering. I almost always feather seems in photoshop. This means
  that feathering has gone to the top of my TODO-List (after I finish
  the metadata processing, which is my current task).


--
Daniel M. German          
http://turingmachine.org/
http://silvernegative.com/
dmg (at) uvic (dot) ca
replace (at) with @ and (dot) with .