[CinCV TNG] [glitch] zoom curve tangent & disjoint

Good Guy good1.2guy at gmail.com
Thu Apr 26 19:55:06 CEST 2018


Hi,

The automation curves in the timeline are evaluated in floatauto.C
as bezier curves, which are cubic polynormals of the form:
y = x**3*(-y0 + 3*y1 - 3*y2 + y3) + x**2*(3*y0 - 6*y1 + 3*y2) + x*(-3*y0 +
3*y1) + y0
y0, y3 = prev / next control values
y1, y2 = prev / next derivitive values

This operation is a cubic "curve fit".
It does not fit an exponential function except in a few
degenerate cases, like zero lengths, zero slopes.

To use a curve fit which has a high effective error,
*USE MORE DATA POINTS.*
There is a great powerpoint presentation:
https://ece.uwaterloo.ca/~dwharder/Maplesque/Bezier/BestFittingBezierCurves.ppt
in slide 14, it shows a great fit with very low error.

I suspect just one more point may be enough to get good results.



On Mon, Apr 16, 2018 at 1:42 PM Sam <cinelerra at posteo.de> wrote:

> I'm about to recreate the font effects from an Adobe Premiere YouTube
> demo for my tutorial.  Unfortunately, I have problems adjusting the zoom
> so that I can make a zoom curve looks like an exponential curve. My zoom
> curve always has a downward curvature. I have attached some photos. I
> remember that it was possible earlier, but something has changed in the
> behavior of the tagent and disjoint. Shortening the line would be
> important to get a more natural zoom. Especially when I fly towards an
> object, the zoom behavior is more like an exponential curve. According
> to the current state (see screenshot zoom curve) I zoom out and then a
> little bit later I zoom in. I don't want to zoom out, but that makes the
> zoom curve current. At the moment this point is not very important
> because I was able to recreate the desired effect with Natron
> Compositing, but it would be nice if we could find a long-term solution.
>
> https://youtu.be/ma9P4nTVtDs?t=19m19s
>
> --
> Sam
>
> _______________________________________________
> Cinelerra mailing list
> Cinelerra at lists.cinelerra-cv.org
> http://lists.cinelerra-cv.org/cgi-bin/mailman/listinfo/cinelerra
>
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