ZoomPath
Logarithmic Moving Path Calculator
- What is it?
- A special calculator for use with Ulead's MediaStudio Pro Video Editing package (versions 5 or 6). It is not necessary with version 7 - see below.
- What does it do?
- Enables a Moving Path to be converted from linear interpolation to logarithmic interpolation
- Why?
- A zoom effect using linear interpolation appears to change speed, with logarithmic interpolation it appears to be constant speed
- Free
- Download the ZoomPath Calculator, it's
free! (current version 0.2.0)
(Note: VB6 runtime is required but not included, it can be downloaded from Microsoft) - More
- The problem
Example
The solution
Screen shot
Other editors
Acknowledgements
The problem
The Moving Path feature in the Video Editor allows you to make a video or still-image clip in the timeline change position and/or size over its duration. It has myriad uses, from picture-in-picture and fly-in/fly-out effects, to pan and zoom of still images. The zoom problem occurs when the size of the image is changed over its duration, and is most often noticeable when working with still images, especially where a deep zoom is used.
What problem?
Suppose you put an image on the timeline (e.g. a scan of a photograph), then apply a moving path to give the effect of zooming in on a certain area. You would expect the result to look like a camera zooming in on the scene. The problem is it doesn't. The zoom seems to progressively slow down as it gets closer in. If you zoom out the same happens in reverse, it appears to speed up as the zoom gets farther out. You might possibly like this effect, but in most cases it's an irritation. The deeper the zoom, i.e. the higher the ratio between the start and end sizes, the more noticeable the effect.
Why does it happen?
It's all to do with mathematics. When the editor calculates all the intermediate points along a moving path it does so using a linear algorithm. That is, the size and position are changed by a fixed amount frame to frame along the entire path. This amount is easy to calculate, as it's the difference between the start and end values divided by the number of frames in the path.
You would expect the result to appear as constant-speed motion, so why doesn't it? If the moving path just changes position, not size, then the linear interpolation of position is exactly right, and the speed of the "pan" effect appears constant. But when changing size it doesn't correspond to our perception. What we perceive as constant-speed zoom is when each step changes the size by a fixed percentage from the preceding frame.
Such a progression is a logarithmic scale, and is how zoom lenses work. When a zoom lens moves at constant-speed it changes the field of view on a logarithmic scale, and so the speed of the zoom appears constant when we watch it.
Example
A picture speaks a thousand words, so here are two example clips showing the effect of the corrections that ZoomPath provides. Both are the result of using a moving path to zoom in on a still image by a ratio of about 6:1.
- The normal result you will get with an ordinary moving path
- The result after applying corrections calculated by ZoomPath
These are Indeo AVI files, about 350KB each. They are highly compressed to minimise download time, so the image quality is low but they fully illustrate the zoom speed effect.
The solution
There is no option in MediaStudio to use logarithmic interpolation in moving paths, but it's possible to create an approximation by adding additional control points to a standard path. What's difficult is working out where to put them and what values to use.
This is where ZoomPath comes in. It does all the calculations, and gives you a list of control point values to set up. Using these you can quickly convert a linear zoom into a near-logarithmic zoom that will appear to be constant-speed when viewed.
Screen shot
This
is a shot of ZoomPath in use. Full details of how to use it are included
in the download.
Other editors
Although this tool was written to solve a problem in MediaStudio Pro, the same problem is found in many other video editing packages. Provided such packages allow control points to be manipulated in a similar way, then it can be used equally effectively with these as with MediaStudio.
If you are able to use ZoomPath with another editor, or you can suggest changes that would make its application more universal, please contact the author.
In MediaStudio Pro version 7, Ulead have added a new option to the Moving Path dialog that causes the editor to perform logarithmic interpolation internally. This renders ZoomPath redundant, but makes life much easier for editors!
Acknowledgements
I identified the Moving Path Zoom problem quite a long time ago, but was unable to solve it effectively at the time. My thanks go to Dean Rose who also encountered it, and corresponded recently with various ideas and suggestions. This re-kindled my interest, and inspired me to do the maths properly! The result is ZoomPath, which I hope you find useful.
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