Ag AF100 & jello or skew correction

Blackout

Blackout

New member
I searched through the gadzillion posts on the main two AF100 threads but does anyone know if the camera will have any sort of process to fix jello or skew issues or can they be expected to be just as bad as on the GH1?

Thanks


Also is anyone reliably using any program that auto detects and fixes skew // cmos jello in post for the GH1 now?
 
The release is six months away. No way we can know anything about relative performance until it comes out. The HPX370 showed substantial jello improvements over the HPX300, but whether that will translate to the AF100 is sheer speculation.
 
Yes, but the difference is far more than that. The AF100 supports full-fledged AVCHD, but the GH1's version is very limited. Its 17mbps isn't as robust as an AF100's 6mbps mode. But if you use the hack to get the GH1 up to 40mbps+, it's very solid at that rate.
 
Yes. If it bears the AVCCAM label, it means it's the full implementation. PH is the highest form of AVCHD out there.
 
i do not believe there would be any way to fix jello in post, right now the majority of the jello/skew issue is due to scan times (i think 25ms for some CMOS cams) whereas the much faster 5ms scan times significantly reduce jello. that is simply a limitation of the sensor design, and nearly all CMOS chips at the moment.

chances are, global shutter will come along affordably relatively soon, and will eliminate jello/skew as well as half-exposure during flashes, etc (basically all rolling shutter issues) and will likely put CCD to rest.

rolling shutter is CMOS' only real weak point at the moment.
 
Yeah Zis.. I agree... global shutter on these chips and 4:2:2 color is the final frontier I guess but I'll take the global shutter over the color first... the jello is holding me back on some things and making me use other cameras that I probably wouldn't need otherwise.
 
the HVX200 doesn't have the jello problem does it? i do a lot of shooting with the camera mounted on a shoulder support... if i were to purchase the AF100 should i be scared of me doing sharp movements with the camera on a shoulder rig and it creating jello? what instances cause jello?
 
the HVX200 doesn't have the jello problem does it? i do a lot of shooting with the camera mounted on a shoulder support... if i were to purchase the AF100 should i be scared of me doing sharp movements with the camera on a shoulder rig and it creating jello? what instances cause jello?
Click to expand...

The HVX 200 uses CCDs and the AG100 will use a CMOS sensor. And the jello and skew are cmos sensors problems. The skew is the bending of straight line objects when you pan. The jello is more an image wobble when you move the camera. Lets hope Panasonic is able to develop their sensors to get rid of these two as much as possible. To me the GH1 is a great improvement on these 2 issues.
 
twerp said:
what instances cause jello?
Click to expand...

Any side-to-side movement, of either the subject or the camera, will cause some skew. Technically, if the movement is greater than one pixel within the read-reset time.

Common times you will make jello: panning, shooting out the window of a car or otherwise "trucking" (that is a camera movement term), filming cars pass by laterally. From the GH1:

1278564735.jpg


Another common side effect happens with camera flashes (for example if you are a wedding videographer and people are taking pictures around you). A camera flash typically is shorter than the read-out time, so it is over before the read-out is done. The result is that half of a frame has a flash and half doesn't. Played at normal time, it probably just looks a little off.

Flash3.jpg


One funny thing with rolling shutter is if you shoot a fan or propeller (with a short shutter). The blades are spinning in a circle. Combine this with top-to-bottom exposure, and you get shots like this (from the new Canon XF-300)

1278562776.jpg


Again, at normal (1/60) shutter speeds, you don't normally see it this distinctly. See http://frankglencairn.files.wordpress.com/2010/07/independent-report-canon-xf300-305.pdf
 
Last edited:
so if i were thinking about getting this camera to shoot fast paced metal videos... where i do a lot of jerky camera movements with the camera on a shoulder rig, or jerky movements while the camera is on a tripod/dolly... i might want to consider sticking to rentals? we shoot a lot of RED... which we rent. own an hvx but haven't used it much recently. was hoping this new af100 would be our in the middle game changer.
 
twerp said:
so if i were thinking about getting this camera to shoot fast paced metal videos... where i do a lot of jerky camera movements with the camera on a shoulder rig, or jerky movements while the camera is on a tripod/dolly... i might want to consider sticking to rentals? we shoot a lot of RED... which we rent. own an hvx but haven't used it much recently. was hoping this new af100 would be our in the middle game changer.
Click to expand...

RED uses a CMOS sensor, so if you haven't noticed it yet, I wouldn't worry about it. Also, not all CMOS cameras are created the same. Some have bigger issues with their rolling shutter than others.
 
twerp said:
the HVX200 doesn't have the jello problem does it? i do a lot of shooting with the camera mounted on a shoulder support... if i were to purchase the AF100 should i be scared of me doing sharp movements with the camera on a shoulder rig and it creating jello? what instances cause jello?
Click to expand...

The rolling shutter is always there. The slanted lines appear when there is motion with contant speed from left to right or right to left. If the motion is vertical, the vertical lines become shorter and longer in length depending on the direction of movement. That's for constant speed.

When speed changes, it gets more interesting. In accelerating/deccelerating movement, the elements are no longer linear, they become curved thought the speed change moments. If you do a left to right pan and stop really fast at the edges and reverse the direction of motion, you will get curved lines which become wavy when you change direction. If you do that vertically (vertical vibration is exactly that) you get the same. This is usually called wobble and looks very interesting if it exists horizontally and vertical or at random angles.

On camera mounts/rigs that eliminate vibration and wide angle lenses that achieve the same, you only get some linear distortion which looks ok if you pan really slow. This is why most online clips from high budget productions look great. The nightmare comes when the wobble appears, and that comes from sudden changes in direction, vibration, hard mounting on vehicles, helicopters, etc.

The geometrical distortion is due to the inability of CMOS rolling shutter to capture an entire frame at once. Interesting because you can get rotating elements to be very distorted or even missing depending on their frequency.
 
Some real world examples:

Panning (slanted lines, minimum bending, looks fine in slow speeds):

http://www.youtube.com/watch?v=Qp_65IQ9U-Q

High frequency vibration with stabilizer (without stabilizer the CCD would be shaky but undistorted and it could be fixed in post):

http://www.youtube.com/watch?v=UEaDrS-yzIE

Handheld (which is low frequency vibration) with very little panning, more noticable on telephoto:

http://www.youtube.com/watch?v=7q8vT53nhaQ

Steadicam and wide angle which eliminate vibration:

http://www.youtube.com/watch?v=77bXddWvVJ8

Fast change in pan direction:

http://www.youtube.com/watch?v=uJpWuISqtg8&feature=related

It's generally usable but you don't want to run with a rolling shutter camera, or mount it to a vibrating vehicle or do action shots with very active camera work.
 
JesterJJZ said:
Yeah but the the AF-100 is a dedicated video camera. Some of these issues should be worked out.
Click to expand...
The AF100 purportedly uses the same sensor as the GH1. If true, because it will be optimized for video, moire and aliasing will be reduced. But it's not clear how much skew or wobble will be reduced as these are due to the read/reset times of the chip. If somehow these can be tweaked, then rolling-shutter artifacts can be mitigated.
 
I believe you can attenuate the shudder in CMOS cameras, but not eliminate it entirely.

That being said, you have to accept the limitation to the extent it exists, and shoot around it.

Huge discussion on this issue over at the HPX300 thread.
 
You must log in or register to reply here.
Back
Top