[Bf-committers] Camera tracking UI

Sergey I. Sharybin g.ulairi at gmail.com
Thu Nov 10 08:56:14 CET 2011


First of all wanted to mention that there's no "Enhanced" or "Super mega 
cool slow" trackers. Well, there can be "Super mega cool" but it'll be 
_really_ slow. KLT and SAD are just different and there can be different 
kinds of features and motions when SAD would give much nicer result than 
KLT. Also, i don't think it's possible to describe in two words when SAD 
works better than KLT. IMO it's just more like: test default settings, 
if result isn't good enough try to tweak some parameters and try again, 
if fails let's try different algorithm.

I've looked into naming problems this morning. Here's image i've already 
sent to bf-vfx: http://www.pasteall.org/pic/show.php?id=20402
Also "Follow Track" constraint can be cleaned a bit: replace 
"Track|Bundle" selector with checkbox "I want this object be parented to 
track in 3d space".

But all this "bundles", "klt" and so is just a terminology like 
"catmull-clark". Why you aren't bored with CC but totally bored with KLT?

One more thing: probably that other software where you don't care about 
tracking algorithm and so are doing some adjustment internally, but we 
can't do such kind of things (@keir: or we can?). Anyway, i don't want 
this to be main goal for next months.

François T. wrote:
>> *What do you propose instead? There has to be some name, either "point" or
>> *
>> * "track". The problem with "track" is that it's highly overloaded. Same
>> with
>> marker. It's not an issue of computer vision, it's an issue of simply
>> deciding on names. It IS important to have a way to refer to each of the
>> different concepts so that there is no confusion.
>> The naming we've chosen for Blender at the moment is:
>> A marker - a 2D coordinate on a single image. Literally, a struct of (x, y,
>> image#, track#)
>> A track - A collection of markers, one per frame, that point to the same
>> physical location in the scene. In other words, a collection of {(x, y,
>> image#)}. There is a 1-to-many relationship between a track and markers.
>> A bundle - The reconstructed 3D point for a track. Called a "bundle"
>> because if you visualize a ray from the camera to each marker, they
>> (should) intersect at a single point for a good reconstruction. The word
>> "bundle" is used to distinguish a reconstructed point from any regular
>> point. There is a 1-to-1 correspondence between a track and a bundle.
>> Here's where the overloading gets confusing:
>> A track*er* - The algorithm that tracks a marker from frame A to frame A+1.
>> In libmv right now, this is KLT and SAD. Ok, there's a few KLT variants but
>> they're similar. This is pattern matching across frames. There needs to be
>> documentation about why you would use one over the other (SAD is faster but
>> less accurate, KLT is very accurate but sometimes slow)
>> A tracker - Also the name used for general matchmoving software, e.g.
>> syntheyes, boujou, etc. Confusing! But there you go.
>> Feature detector - An algorithm to identify "good features to track" in the
>> image, for automatic tracking. Again, the best algorithm depends on the
>> scene. I wish there was One True Feature Detector To Rule Them All but
>> there isn't.*
> exactly what I meant !!!! I don't care about all this different stuff. On a
> artist point of view the workflow is simple.
> You have 2d Tracks and a solve .... tada, the rest (structure, set of
> frames, blablabla,....) don't take it the wrong way but nobody cares :)
> That's the reason why, like you said, the general software just call that
> trackers. But I'm sure the coders from those software have some crazy names
> as well to make a slight different between a structure thing and keyframe
> other thing ... don't even know what I'm talking about :p
>>> Same confusion with, markers, trackers, ....
>>> Same with algorithm FAST, SAD, ... all technical stuff that doesn't mean
>> a
>>> thing if you havn't done any computer vision dev in your life
>> I don't think we can avoid having good documentation.
> If one is better than the other but slower called it "enhanced tracker" or
> "super mega cool slow tracker" .... :)
>> But in another hand, matchmove is something you have to get interest in as
>>> well. it is a discipline and not just a camera to move around :p. There
>> are
>>> terms you got to know as well. Reconstruction is a common one for
>> instance.
>> The difficulty is that if everything is made automatic with no choices,
>> then the tool is less useful since in many situations the difference in
>> whether you can track a shot or not depends on which algorithm you pick.
>> Welcome to computer vision, where the pixels don't care what you want :)
> Dont give me wrong, I have been working on both side R&D and Artist. I know
> the need of all the details stuff on the dev side. But front-end doesn't
> need all that. And by no mean I meant everything should be hidden or
> automatic. I also know that FAST or SAD WON'T mean a thing to most peoples.
> And even if they look into matchmoving books or tutorial from other
> software (since our workflow is similar to other any technics could be
> applied)... they won't find the anwser. They'll have to get into computer
> vision (the dark side for the artist) to understand the difference.
> It's like go ask a modeler what a matrix is :) ... he won't even know it
> does exist, and still he is using it each time he moves something around
>> So yeah on the overall, lots of cleaning stuff to do, and lets drop the
>>> geeky dev side. This is a tool for artist and not for devs as far as I'm
>>> concern
>> Do you have concrete proposals to do so?
> We can definetly work on that and take time to do a nice proposal.
>> Keir
>>> 2011/11/9 Daniel Salazar - 3Developer.com<zanqdo at gmail.com>
>>>> Hi, i see that camera tracker related UI is spread all over the place
>>>> with no clear definition. Camera tracking is a corner case use of
>>>> Blender, I'd suggest that UI elements belonging to it get clearer
>>>> names *and* get pulled together in boxes or their own panels
>>>> ie: follow track constraint
>>>> http://www.pasteall.org/pic/show.php?id=20349
>>>> why would any regular user of know that this is camera tracking stuff,
>>>> or what is a Bundle?
>>>> it's worst in the N Panel
>>>> http://www.pasteall.org/pic/show.php?id=20350
>>>> Shading, Textured solid.. reconstruction? reconstruction of what??
>>>> bundle, bundle, bundle and then the old quad view!
>>>> Daniel Salazar
>>>> 3Developer.com
>>>> _______________________________________________
>>>> Bf-committers mailing list
>>>> Bf-committers at blender.org
>>>> http://lists.blender.org/mailman/listinfo/bf-committers
>>> --
>>> ____________________
>>> François Tarlier
>>> www.francois-tarlier.com
>>> www.linkedin.com/in/francoistarlier
>>> _______________________________________________
>>> Bf-committers mailing list
>>> Bf-committers at blender.org
>>> http://lists.blender.org/mailman/listinfo/bf-committers
>> _______________________________________________
>> Bf-committers mailing list
>> Bf-committers at blender.org
>> http://lists.blender.org/mailman/listinfo/bf-committers

With best regards, Sergey I. Sharybin

More information about the Bf-committers mailing list