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Strange artifacts on Frame Blending

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Randy McWilsonStrange artifacts on Frame Blending
by on Dec 14, 2009 at 4:17:28 am

I am using 720 60p footage from a Canon 7D (H.264) and doing some slo-mo tests. It is a very basic outdoor shot of a dog running laterally being followed in a smooth pan. I have executed a time stretch to 300% normal time, then applied pixel motion frame blending. The beginning of the slo-mo is gorgeous, but then, strange artifacting appears around the ears and nose of the dog, and sometimes in the hair around some of the larger spots on the Australian Shepherd. I have used frame blending with amazing results many times in the past, but this is the first occurence of artifacting, or of any negative issues.

Any ideas?

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Dave JohnsonRe: Strange artifacts on Frame Blending
by on Dec 14, 2009 at 3:51:39 pm

It sounds like there are at least two separate issues contributing to the less than ideal results ...

[1] H.264 doesn't contain complete image data in every frame, only at keyframe intervals ... so, using interframe media as a source is always bad (see Dave LaRonde's "stock answer #1" for details), but the issues will be more extreme when time remapping since there is so little image data for the frame interpolations to be based on.

[2] 300% is quite a stretch ... that degree of slo-mo is usually best accomplished by shooting in slo-mo and only using post methods for relatively small adjustments.

Since you might be past the point where you could address either issue in the ideal way (re-shooting with the end result more in mind), one option to consider is hiding the artifacts with other effects like forcing motion blur onto the subject (if the artifacts aren't too extreme and additional effects would fit the situation).

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Randy McWilsonRe: Strange artifacts on Frame Blending
by on Dec 15, 2009 at 6:40:37 am


Thanks for that reminder about inter-frame encoding. I hadn't even taken that into consideration as a possible source of the artifacting. As far as 300%, I have had good results with even up to 400%, as long as the footage was intra-frame.

Maybe transcode the H.264 into a more robust stream and try again?

Eternity...don't miss it for the world.

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David JohnsonRe: Strange artifacts on Frame Blending
by on Dec 15, 2009 at 12:37:17 pm

Glad to help, Randy. Yes, I'd definitely transcode the footage ... perhaps to a MOV with the lossless PNG video codec (not a PNG image sequence) or the lossless Animation codec.

No doubt you can do extreme time-remapping via software only ... I just meant that best results are usually gained with a combination of both in-camera and software methods so whether you get adequate results depends on your particular footage and requirements.

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