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Author Topic: Optical flow  (Read 2607 times)

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« on: February 04, 2018, 06:31 »
0
Hi all!
[This is similar topic to KB's recent topic, but this one is only about optical flow and it's impact on video quality.]
I'd like to make a slow motion clip, but my camera does only 1080 60p. I import my footage into FCPX and conform clip to 24p. I get 2.5x slow motion. Let's say I want 3x or 4x slow motion. Should I use optical flow? How is it going to impact video quality? Will it be good enough for stock? What's your experience?


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« Last Edit: February 04, 2018, 06:34 by smcbuki »


« Reply #1 on: February 04, 2018, 06:45 »
0
Hi all!
[This is similar topic to KB's recent topic, but this one is only about optical flow and it's impact on video quality.]
I'd like to make a slow motion clip, but my camera does only 1080 60p. I import my footage into FCPX and conform clip to 24p. I get 2.5x slow motion. Let's say I want 3x or 4x slow motion. Should I use optical flow? How is it going to impact video quality? Will it be good enough for stock? What's your experience?


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There is no one answer to this. Except "it depends".

You need to try it on a clip to clip basis.

Generally, if there isn't a lot of movement between frames, and not too many details (like leaves), it will work well. If there is a lot of movement or small details, you will get artefacts.

To answer your question "should I use optical flow": yes. Or a third party alternative like Twixtor, which is essentially optical flow with more options, like masking.

Frame blending usually looks pretty ugly, but can work sometimes.

---

You can only ever fake something convincingly to a certain extent.

To sum up: it will only look nice if the motion is already slow and even, and you want to make it super slow.
« Last Edit: February 04, 2018, 06:47 by increasingdifficulty »

« Reply #2 on: February 06, 2018, 23:51 »
0
Hi all!
[This is similar topic to KB's recent topic, but this one is only about optical flow and it's impact on video quality.]
I'd like to make a slow motion clip, but my camera does only 1080 60p. I import my footage into FCPX and conform clip to 24p. I get 2.5x slow motion. Let's say I want 3x or 4x slow motion. Should I use optical flow? How is it going to impact video quality? Will it be good enough for stock? What's your experience?


Sent from my F5 using Tapatalk

There is no one answer to this. Except "it depends".

You need to try it on a clip to clip basis.

Generally, if there isn't a lot of movement between frames, and not too many details (like leaves), it will work well. If there is a lot of movement or small details, you will get artefacts.

To answer your question "should I use optical flow": yes. Or a third party alternative like Twixtor, which is essentially optical flow with more options, like masking.

Frame blending usually looks pretty ugly, but can work sometimes.

---

You can only ever fake something convincingly to a certain extent.

To sum up: it will only look nice if the motion is already slow and even, and you want to make it super slow.
Thank you for your answer. Yes, I guess it depends from the actual footage. From what I saw on YT, people use it for "near freeze" effect. They take just couple of frames and slow them down like 100x. The result looks interesting, but it's not what i need. I was wondering if I could slow down footage where I pour various liquids (milk, wine...), but I guess results will be very bad since there is a lot of movement. I'll give it a shot, but I don't think it is going to work.

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« Reply #3 on: February 07, 2018, 00:41 »
0
Results are also tied to contrast and movement between foreground, subject, and background.

As an example: If you are pouring while milk out in front of a locked off camera with a black background youll have the best chance for an acceptable effect.

Noise also reduces the accuracy of the effect so make sure your footage is well lit.

Last thing I have noticed is that optical flow often falls apart the longer its used on a clip, so if you can keep your clip durations shorter, between 7-10 seconds, that might help as well.

« Reply #4 on: February 07, 2018, 02:15 »
0
Thank you for your answer. Yes, I guess it depends from the actual footage. From what I saw on YT, people use it for "near freeze" effect.

Yes, near freeze works well because the source footage is already very slow.

Filming liquids at 60p is most likely not going to be enough. If you filmed it at 96p or 120p it might work well though, slowing it down even more.

But just go for it and you shall see.  :)


 

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