GH4 video judder/strobing - a solution

Bassman2003 wrote:

I tried to read a lot of this thread but it all seems to be a general lack of understanding about 24p and how to shoot with it.

* I'll quit this discussion if this thread is getting irate *

It's a simple equation, filming rate (fps) and display rate (refresh Hz), if they are equal or multiples they there is no frame doubling required.

Frame doubling is required is they are not multiples. There can be no dispute.

TV's especially, and some monitors can interpolate frames, termed 'smooth / fluid motion', etc, similar to in-between frames rendered by video editors. This is still a work-around, though looks ok.

Most adverts made in the US shown on UK TV's judder, 29fps with no rendered in-between frames, frame doubling is required, it looks ugly.

Basically DO NOT PAN with 24p!

With the GH4 and most pro cinema cameras shutter speed is set in terms of shutter angle [not shutter speed], generally 180 degree angle is recommended - as this equates most closely to the 'maltese cross' shutter of traditional film cameras [while the film frame is advanced]. 180 deg is double the fps, so 1/48th second.

I even use 360 degrees, which leaves the shutter open for the whole fps interval, which for 24fps is 1/24th sec.  This achieves perfect blur from one frame to next.

On a 60Hz refresh, this still requires pull-down, and judder is still visible.  It's nothing wrong with the GH4, is just that 24 into 60 doesn't go.

If you watch movies they rarely pan. Panning is rotating the camera from a fixed position. In cinema they move the camera, not rotate only. 24 frames per second is just too slow to keep up with a panning style motion and make it look smooth unless you go super slow.

I successfully pan (with 25fps as I shoot with Europe broadcast standard rather than film 24fps but the difference is minimal), actually I avoid panning quickly as it's actually too quick for the brain to comprehend what's in the shot!!

Though also very very quick panning is ok, a kind of here-and-there view - it's so quick; but in terms of slow smooth panning, 24fps pans look totally smooth - on a display capable of 'cinema' 'fluid motion' or '48Hz'.  On a display not capable of that it will judder.  NTSC, 29.97fps looks great on a 60Hz display as the math nearly works, you just get a frame doubled every 700 frames - you might not notice that judder - may be when you blink!

You have to learn how to film in 24p. It will tell you what works and what does not work. If you see judder then it did not work and you need to analyze what you might be doing wrong.

The classic approach is to not move the camera unless the subject of your shooting is moving. By moving the camera with the subject, the subsequent background judder is not "noticed" by the viewer. It is still there, you just do not concentrate on it. Shallow DOF helps a lot as well.

Hope this helps clear up some of the incorrect information in this thread. Good luck and it is not the fault of the GH4.

No it's not, but the GH4 for many new film-makers raises these issues and questions.

The purpose of this thread is to help new film makers, who using the GH4, would benefit from positive advise.

The monitor / display *does* have a significant impact on smoothness / judder of video play-back.

And as you point out the art of filming does also - not panning too quickly - though 24fps panning is fine - and has been since the creation of cinema [though just don't judge 24fps on the fixed 60Hz LCD of your laptop].