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Stabilised Footage loses resolution.
Hi all,
I have a shot which has been stabilised in order to carry out a repair on it. During the repair the footage remained in the original codec, aspect ratio, frame rate, colour space and frame size which it was supplied in (ProRes HQ).
I’m using AE CS5 on PC. The shot was supplied having been rendered out of FCP7. I worked on it then handed the AE project file back to the mac owner for rendering with AE CS5 on his system, enabling the shot to not need transcoding.
I have now been told that the shot has lost some of its sharpness.The best information I can give as to the extent of this is that there has been a ‘slight’ loss of sharpness.
The suspected cause is AE’s built in tracking/stabilising facility using sub-pixel interpolation. Has anyone experienced this problem before, and able to confirm or deny it? I could possibly use Mocha if its planar tracking will resolve the issue, again some advice would be appreciated if anyone is able to help.
Many thanks,
Anthony.
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3 Replies
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Using mocha or not wouldn’t cause any change in sub-pixel interpolation. This result comes from the positioning of a layer on non-integer values. Any tracker will do this.
See this page for details of subpixel positioning and interpolation. Note that setting the layer to Draft quality turns sub-pixel interpolaton off.
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A number of possibilities as to the cause of the loss of sharpness –
1) [Anthony Smith] “The shot was supplied having been rendered out of FCP7”. Check if this may be a likely issue. IOW, tell your clients to import exported footage back onto their timeline to ensure that their export is lossless or as they would like it to be. Occasionally, this part of the workflow is the culprit.2)[Anthony Smith] ” I worked on it then handed the AE project file back to the mac owner for rendering with AE CS5 on his system, enabling the shot to not need transcoding.”
Assuming step 1 has been accomplished and you should proceed on your end. There is another possible workflow issue here which involves the manner and settings in which the movie from the AE file has been rendered/exported/imported into FCP.
Subpixel interpolation isn’t an issue in and of itself. To stabilize a shot, you will very likely want subpixel interpolation to kick in. Hence, you will want to ensure that your layer is always set to Best Quality.
Resampling is also a possible cause to your issue.
With respect to the Position and Anchor Point properties, AE resamples an image when (a)a layer is animated and it is set to Best Quality and (b) a layer is static and the difference between the Anchor Point and Position is not an integer.
The above paragraph is taken from Chris & Trish Meyers’ excellent “Creating Motion Graphics with Adobe After Effects” book.
Assuming that your issue only involves static frames, first or last, you can easily fix the problem by changing the values of either the Anchor Point or Position at the problem keyframes (first and last) to ensure that (b), above, doesn’t occur.
if your issue kicks in when the layers are moving then try the following Expression script in both the Anchor Point and Position properties.
// Removes resampling artefacts. Paste into Position & Anchor Point.
// Start of Script
TestX = (transform.anchorPoint[0]/transform.position[0]);
TestY = (transform.anchorPoint[1]/transform.position[1]);
TestResult = TestX%TestY;
AbsoluteTestResolute = Math.abs(TestResult);
if (AbsoluteTestResolute > 0) {
IntegerValX = Math.round(value[0]);
IntegerValY = Math.round(value[1]);
[IntegerValX,IntegerValY]
} else {
[value[0],value[1]]
}
//RoRK – Roland KahlenbergI’ve only just written this script and done only minimal testing with it. Hopefully it can be improved by someone else if the idea is sufficiently useful.
Another possibility is that you may have enlarged your image to the point where it becomes soft. IOW when resampling occurs (due to scaling an image) with too few pixels in the source to fill the composition without enlarging and softening the image.
With stabilization, you almost always have to enlarge the image, post-stabilization, to ensure that your image fills the composition panel. To reduce the amount of scaling you will have to do, try to pick a spot for stabilization that is closest to the center of your layer.
Another alternative is for you to use Inverse Stabilization since you’re only applying stabilization for the purpose of applying an effect. Check out COW Reverse Stabilzation tutorial.
HTH
RoRKAE Training in South East Asia. AE templates for sale and rental. Click here for more
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Stabilization always softens shots. After a shot is stabilized, it must be scaled up to fill the frame, cropping off the original footage’s edges which are revealed by the stabilization. The more you scale, the softer it gets.
Careful use of Unsharp mask might help.
Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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