[Bf-vfx] Blender camera tracking approach

[Lorenzo Pierfederici]

Tobi,

all the best with your effort!
I think that a detailed workflow like the one Tom posted is very important,
and it will help when it's time for gui/docs.

I'd suggest two more points based on what we do here:
- alongside 2c you can use a standard distortion chart (a special grid image
that you shoot with your camera on set at the same time as the actual
shooting)
- the system should allow for manually tweaking track points frame by frame:
there are scenes that you just can't track well enough and some manual
tweaking is often needed to fix some small slipping that on a theatre screen
would look very bad!

and keep in mind that lenses suffer not only from distortion but from color
aberration, too.

I agree with Francesco that the un/distortion process should leave options
open, in many cases you _want_ to degrade the cg render a bit to make it fit
better.
But (as long as one can choose) I think that the idea of integrating it into
a blender camera is very interesting! (and it could have many interesting
uses in animation, too)

good luck!
lorenzo


On Sun, May 8, 2011 at 2:57 PM, Francesco Callari <fgcallari at gmail.com>wrote:

> A couple of comments.
>
> 1. Whether the final composite is done on the original plate or a lens
> distortion-corrected (i.e. undistorted) one is an artistic decision, not
> just one based on image quality.   The production crew may want to remove
> the plate distortion, leave it unchanged or modify it as the shot demands
> from an artistic point of view (I have seen shots in which the lens
> distortion was intentionally magnified). The tools should support their
> decisions whatever they are. The image quality argument may be moot if the
> original plate resolution is higher than the final one and the distortion is
> moderate.
>
> 2. From a practical point of view, re-distorting the CG upon rendering so
> it matches the original (lens-distorted) plate is just one way to prepare
> the elements for compositing. It may not the the most efficient way, and it
> may even be impractical when the compositing is done with a tool other than
> Blender, or when some of the CG assets come from other tools. In these case
> the preferred alternative is to expose the calibrated lens distortion to the
> compositing tool. A common way to do this is by having the matchmoving tool
> export an "offset map", i.e. an image whose red/green channels encode
> per-pixel the amount of x/y distortion. Many compositing tools (e.g. Shake)
> can import such images in a variety of formats. This ability to export the
> distortion as an image is a basic requirement.
>
> On Sun, May 8, 2011 at 6:49 AM, Tobias Kummer <supertoilet at gmx.net> wrote:
>
>> Hey all!
>>
>> Here are some of my thoughts on the matchmoving workflow in blender,
>> after some discussion in IRC chat. Since I've never used Pfmatchit, I
>> cannot say anything about it, but when Syntheyes was mentioned I looked
>> into it a little and thought its workflow might be suboptimal.
>> It re-applies lens distortion on an image post-processing level, which
>> is bad quality-wise. A better way would be setting blenders camera
>> parameters, so the rendered output already has matching distortion and
>> does not have to be altered afterwards (which brings up the topic
>> blender real world camera settings - would be desirable anyway).
>> See this (crappy) flowchart as illustration:
>> http://www.pasteall.org/pic/12079
>>
>> The first step in the proposed workflow accomodates for the fact that
>> blender cannot draw lens distortions in the 3D viewport. So the
>> outcoming undistorted footage is just used for visualisation purposes
>> for the artist - for rendering/compositing, the original distorted
>> footage would be used. This way, we skip the step that compromises
>> quality.
>> As blender will have combined 3D/tracking functionality, we should
>> leverage on that and not copy the tracking-only workflow of other
>> packages.
>>
>> Please correct me if there are any major mistakes in my thoughts!
>>
>> Greets,
>>
>> Tobias
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>
>
>
> --
> Franco Callari <fgcallari at gmail.com>
>
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>
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>
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