Rolling shutter and lightning footage

[Mikko Lopponen]

There's some bending when the cars pass. Now this clip is 60p. What happens when you convert that to 30p by deinterlacing or to 24? It will show the bending way worse. That's one reason why people don't see the effect as much and think that the hv20 has more of it than other cams.

BUT it also looks like the hv20 has a faster rolling shutter rate. But I'd have to try the cam myself to be sure. I've seen clips of hc3 where it looked like there was no rolling shutter only to find out it myself. It does look very promising.

The material is beatiful anyway. Great colors.

[Jack Kelly]

Originally Posted by Mikko Lopponen

There's some bending when the cars pass. Now this clip is 60p. What happens when you convert that to 30p by deinterlacing or to 24? It will show the bending way worse. That's one reason why people don't see the effect as much and think that the hv20 has more of it than other cams.

Hi Mikko - thanks loads for the reply.

I'm confused - why would converting 720/60p to 720/30p help to eccentuate the rolling-shutter distortions? Surely the conversion from 720/60p to 720/30p just throws away every other frame?

Originally Posted by Mikko Lopponen

(quote taken from here)

The difference that HV20 "apparently" has is because it has a 24f mode that shows the distortions more. When you use 60i it will look the same as in hc7 etc.

I'm pretty sure that Russ Anderson's now infamous "crooked lamp" footage was shot at 1080/60i (actually 59.94i) on the HV20:

http://www.ssontech.com/content/crooked.mov

(the properties for the .mov file state that it's 29.97fps and the video was clearly shot interlaced - just look at that combing!)

In other words: both Russ Anderson's "crooked lamp" footage and Jack Zhang's "Stanley Park Sunset and Nighttime (720p60)" were both shot at 1080/60i. The differences are that Russ's footage was shot with an HV20 whilst Jack's was shot with an HC7 and then converted to 720/60p in post. I can't see why the conversion from 1080/60i to 720/60p would affect the rolling shutter effect so the conclusion that I draw from this comparison is that the HC7 is less prone to rolling shutter artefacts than the HV20.

[Jack Zhang]

On topic with this thread, I was lucky enough to catch a bolt of lightning with my HC7 yesterday and the video is now up on Stage6 (heck, I even uploaded it to The Weather Network... (Canadian version of the Weather Channel))

Stage6 is having trouble right now so I'll give the link later.

[Jack Kelly]

Originally Posted by Jack Zhang

On topic with this thread, I was lucky enough to catch a bolt of lightning with my HC7 yesterday

Great work! What was the result? Did the video you captured display rolling-shutter artefacts?

[Jack Zhang]

The initial flash was not captured at full brightness... so I don't know what that would mean...

And to the conversion question: I used Vegas 7.0e with smart resample and interpolate fields to render the video portion in 720p60. then I muxed the audio in later with virtualdubmod.

[Jack Kelly]

OK, this is starting to really confuse me! I've been searching Stage6 for HV20 videos to try to find evidence for the camera's slow rolling shutter.

Here's a video of a BMW M5 demo shot on an HV20 which includes lots of very fast pans and some footage shot from a moving car:

http://stage6.divx.com/user/emjoyner...---Spartanburg

I can find any serious distortions in that video.

Urg. Maybe Canon and Sony could tell us the speed of their rolling shutters?! I'll write to them both now.

Jack

[Ian G. Thompson]

I film myself flying down 95 south almost every weekend going about 85mph. I have no problems with rolling shutter artifacts. Video comes out looking smooth every time. I actually mount the cam on my tripod and the tripod in my cupholder. Works great.

My setup: http://www.fortvir.net/gallery/v/P3U_videos/Ian-T/

[Jack Kelly]

Thanks for the reply, Ian.

What frame rate did you use on the HV20? 1080/60i?

Thanks,
Jack

[Mikko Lopponen]

Originally Posted by Jack Kelly

Hi Mikko - thanks loads for the reply.

I'm confused - why would converting 720/60p to 720/30p help to eccentuate the rolling-shutter distortions? Surely the conversion from 720/60p to 720/30p just throws away every other frame?

It's because one frame stays longer in view. Remember also that with a 1/60 shutter the motion blur will blur a lot of the smaller rolling shutter artifacts away.

(the properties for the .mov file state that it's 29.97fps and the video was clearly shot interlaced - just look at that combing!)

If you see the combing you are looking at it at 29.97, not 60 fps.

Here's a video of a BMW M5 demo

That's a badly encoded video. It has blended the fields here and there and something has gone wrong when doing 24p material. It's pretty hard to see anything in the moving parts because of double blurring of the fields. I could still see the telltale bending going on when the camera shook. When you start spotting that the upper part moves at a slightly different time than the lower part of the picture, it's kinda annoying. But the bad encoding masked movements anyway.

Here's an old clip from my hc1

http://hmcindie.pp.fi/rollingshutter/

A high shutter reveals the effect very well. Remember that the effect is always there. It's just hidden from view when there is motion blur. It's still possible to make action shots with the hc1, it's just another hurdle to remember about.

[Ian G. Thompson]

Originally Posted by Jack Kelly

Thanks for the reply, Ian.

What frame rate did you use on the HV20? 1080/60i?

Thanks,
Jack

I used 24P.

[Ian G. Thompson]

Well...just like Jack....I can't find any serious distortions in that BMW footage. I know there are some artifacts...but all in all...that looks good to me especially with the conditions that cam was in.

[Jack Zhang]

Ok, I think I might've produced distortions in the HC7 this time around crossing the Lions Gate Bridge.

Stage6 is acting weird so I'll post a screenshot.

[Jack Kelly]

Originally Posted by Jack Zhang

Ok, I think I might've produced distortions in the HC7 this time around crossing the Lions Gate Bridge.

Stage6 is acting weird so I'll post a screenshot.

Thanks for the screenshot. Hmm... the vertical supports certainly aren't exactly perpendicular to the horizontal railing.... but the vertical supports are bending the wrong way! I'm pretty sure that all rolling-shutter mechanisms on CMOS sensors start reading at the top of the sensor (so the top row is taken first, then the second row, then the third row and so on...). The HV20 sensor certainly starts from the top. If the sensor starts reading from the top then you'd expect the top part of the supports to be further to the *right* of the image than the bottom part. But that's the opposite to what's shown in that screenshot.

[edit - see the post below]

Ho hum.

Both Canon and Sony have promised to call me this morning to let me know about their rolling shutters.

What ever happens, I have to order either an HC7 or an HV20 this afternoon. I think I'm going for the HC7. Even if the HC7 and HV20 do have the same speed rolling shutters, I really like the 240-fields-per-second-for-3-seconds feature of the HC7. I love smooth slow-mo. I am really gutted that the Sony doesn't have "true progressive scan" but I've done some tests with motion-compensated de-interlacers and I'm happy that good de-interlacing can produce an image that's almost as pretty as a true progressive-scan image.

[Jack Kelly]

Originally Posted by Mikko Lopponen

If you see the combing you are looking at it at 29.97, not 60 fps.

Yes, but it was shot 60i (60i = 60 fields per second = 30 (interlaced) frames per second)

Originally Posted by Mikko Lopponen

That's a badly encoded video. It has blended the fields here and there and something has gone wrong when doing 24p material. It's pretty hard to see anything in the moving parts because of double blurring of the fields. I could still see the telltale bending going on when the camera shook. When you start spotting that the upper part moves at a slightly different time than the lower part of the picture, it's kinda annoying. But the bad encoding masked movements anyway.

I'm not sure I agree. Ghosting is an fairly inevitable side-effect of resolution-maintaining de-interlacing (even motion-compensated de-interlacers like MVbob produce some ghosting). Even using a top-of-the-line hardware de-interlacer will produce some ghosting. As far as I'm aware, the only way to de-interlace without producing ghosting is to throw away one of the fields. So, in other words, I would propose that ghosting does not equal bad encoding. But, more to the point, even bad encoding shouldn't completely hide the effects of a rolling shutter. Bad encoding wont change the angle of the rolling-shutter distortions.

Originally Posted by Mikko Lopponen

Here's an old clip from my hc1

Thanks loads for that. That certainly does contain some nasty rolling-shutter artefacts! And, very interestingly, that clip seems to suggest that the HC1 starts reading from the *bottom* of the sensor (the verticals seem to lean *into* to pan). If we assume that the HC7 also reads from the bottom of the sensor then this explains Jack's screenshot above.

[Jack Kelly]

Hi,

Sony called me this morning. I was impressed that they called me back but they really didn't get what the issue was. After I spent 10 minutes trying to explain what the rolling shutter issue is, the customer services guy went off to speak with the "camera person". He tried to fob me off by trying to persuade me that the issue is that shooting interlaced produces comb-lines when displayed on a progressive screen like a computer screen. They really didn't understand that the issue is all to do with the read timings *within* each field. So, the bottom line is that Sony told me nothing of value.

Still... I've run out of research time so I'm going to dump £700 on an HC7 this afternoon.

Quick rant: I'm really glad that "modern" companies like Cineform and Red "get" that it's not acceptable to separate tech support from the engineers who design the products. Consumers are intelligent people who want detailed answers. Large companies like Sony and Canon should take a long, hard look at how these smaller, more customer-focussed companies are handling their customer support.

Jack