CMOS=Jello Right?

[cameronchapman]

I've seen a lot of posts with people who want to upgrade their (usually older or consumer-grade) camcorder to something more professional/pro-sumer level. A lot of these posts mention getting a DSLR, and inevitably those posts turn to the weaknesses of the DSLR, most notably rolling shutter or jello effects, which is caused by the CMOS sensor used in DSLRs (and a lot of other cameras).

Yet I never hear rolling shutter/jello as the reason these people want to upgrade. A lot of consumer-grade camcorders use CMOS sensors (as do a lot of pro-sumer and professional camcorders, including the Red, which has documented rolling shutter artifacts). And yet this argument seems to be used most heavily against DSLRs.

Now, not trying to single anyone out here, but just today I saw a thread about the Canon Vixia HV30 vs. a hacked GH1. The HV30 uses a CMOS sensor, as does the GH1, and yet the poster specifically stated they were worried about jello with the GH1. Have they never experienced jello with the HV30? Am I completely missing something with regard to the CMOS sensors used in camcorders as opposed to the ones used in DSLRs? I have very little experience with camcorders (a Kodak zi8 is probably the most advanced camcorder I've used, and I can tell you now that that thing has the worst jello effect I've ever seen), so I really don't know.

Or is this something that's being used against DSLRs as a way to discredit them, when it really applies to a much larger group of equipment? I sometimes get the feeling that that's the case...

 

[Gonzo_Entertainment]

I bet that's it David. I imagine the Red has some kind of in camera system that tamps it down a bit. Otherwise with that big ass sensor it would be a major issue. As I said, even a moderate pan, not even close to a "whip pan" requires post cleanup on my 5D.

 

[CamVader]

I bet that's it David. I imagine the Red has some kind of in camera system that tamps it down a bit. Otherwise with that big ass sensor it would be a major issue. As I said, even a moderate pan, not even close to a "whip pan" requires post cleanup on my 5D.

But your 5dMII sensor is much larger than a RED which is super 35 (about the same as a 7D), well depending on the model.

Ah! Just read that rolling shutter is handled by firmware in RED cameras. I just Wiki'd it. I learn something new every day here.

 

[brettzdamn]

I learn something new every day here.

I learn 10 things new here everydayb

 

[CamVader]

I learn 10 things new here everydayb

So true.

 

[rayw]

My camera has a 1/2.5 CMOS sensor and I've noticed that if the shutter speed is knocked down to around 60 or 30 the jello diminishes greatly.
Of course, the aperture tightens down and DoF lengthens out, so...

It's the high shutter speeds that make jello-ing worse.

 

[Gonzo_Entertainment]

My camera has a 1/2.5 CMOS sensor and I've noticed that if the shutter speed is knocked down to around 60 or 30 the jello diminishes greatly.
Of course, the aperture tightens down and DoF lengthens out, so...

It's the high shutter speeds that make jello-ing worse.

Yeah I have experimented with shooting in 1/40 instead of 1/50 at 24P for both jello and aliasing with some success.

 

[rayw]

So no hard panning while trying to capture your SAVING RYAN'S PRIVATES and 28 DAYS/WEEKS later choppy-cam.

This is the sort of creative work-arounds I was babbling about in another thread.

A sensible pan speed with a high shutter speed + whoppin' aperture setting will work fine.
Just trying to do all three (whip-pan+1000 shutter speed+1.8f) at the same time is kinduva PITA.

How many whip-pan shots do you guys run across, frankly?

And Gonzo, I haven't even considered the frame rate.
I'm still tinkering with new equipment to learn it's limitations and haven't EVEN gotten as far as monkeying around with 24/25 vs. 30 vs 60.

I have a decent handle on the ShutterSpeed/Aperature/Focus relationship triangle.
How does frame rate bugger with all those?

 

[Gonzo_Entertainment]

Well Frame rate would make 4.. one too many sides for a triange!

To my knowledge it has no effect on exposure. What it effects is the amount of motion blur in the image. Slower frame rates like 24 tend to blur motion a bit (which we associate with a "film" look. Where higher rates look very "crisp" (which we associate with TV).

On a big sensor camera like a 5D it doesn't take a whip pan. Even a moderately fast pan will cause rolling shutter. This makes sense because the larger the sensor the longer it takes to scan all the lines, the more pronopunced the roll.

 

[cameronchapman]

Memory hasn't been serving me right lately, but here goes. I remember reading about the sensor used in at least one of the RED models that was something like 5MP, but didn't skip lines like DSLR's do and had no rolling shutter issues (because it didn't skip lines).

DSLR's skip every 3rd line and that's why you get the jello effect because, when panning, the information at the top of the sensor is read first and by the time it gets to the bottom the image has moved.

Anybody recall RED's not line skipping?

It's not the line skipping that causes it, it's the fact that it scans from top to bottom, so by the time it reaches the bottom, things have moved in relation to where they were on top. Also, it's just the Canons (and maybe Nikons?) that skip entire lines on the sensor. The Panasonics use a different kind of sampling (I wanna say it's bicubic on the Panasonics and bilinear on the others, but I could be completely wrong about that).

I would think that when the RED is shooting at full 4k RAW, it's recording on the full sensor. And I bet that it does bicubic sampling rather than skipping lines when it's not recording to the full sensor.

 

[CamVader]

It's not the line skipping that causes it, it's the fact that it scans from top to bottom, so by the time it reaches the bottom, things have moved in relation to where they were on top. Also, it's just the Canons (and maybe Nikons?) that skip entire lines on the sensor. The Panasonics use a different kind of sampling (I wanna say it's bicubic on the Panasonics and bilinear on the others, but I could be completely wrong about that).

I would think that when the RED is shooting at full 4k RAW, it's recording on the full sensor. And I bet that it does bicubic sampling rather than skipping lines when it's not recording to the full sensor.

Sometimes the conflicting information is enough to give a guy a headache. I had to backtrack to where I read this, or thought I read this. I'm just providing this link so you don't think I pulled it out of my rear.

Now rolling shutter is a problem that all CMOS-based cameras (and these are, in fact, almost all new camcorders out there today) face in a more or less bad way. Instead of reading out the sensor at once (how it used to be with CCD cameras), CMOS sensors are read out sequentially, one line after another. That means that the bottom of every single still frame isn’t recorded in the exact same moment as the first lines. This isn’t much of a problem in most shooting situations, but everything that’s moving to fast will look skewed – be it the camera itself (quick pans) or a fast object (try a tramway or a truck on the highway shot from the side).

So yes, all CMOS-based cameras have this problem, but it is MUCH worse with DSLRs because of the line skipping: As I said, their resolution is much higher because of the still image function of these cameras. Therefore, there are simply more lines to be read out. Most of the lines are skipped when recording video, but that doesn’t mean that the remaining lines can be read out any faster than before. This results in even worse skew than with most other cameras. Link

 

[cameronchapman]

Sometimes the conflicting information is enough to give a guy a headache. I had to backtrack to where I read this, or thought I read this. I'm just providing this link so you don't think I pulled it out of my rear.

Now rolling shutter is a problem that all CMOS-based cameras (and these are, in fact, almost all new camcorders out there today) face in a more or less bad way. Instead of reading out the sensor at once (how it used to be with CCD cameras), CMOS sensors are read out sequentially, one line after another. That means that the bottom of every single still frame isn’t recorded in the exact same moment as the first lines. This isn’t much of a problem in most shooting situations, but everything that’s moving to fast will look skewed – be it the camera itself (quick pans) or a fast object (try a tramway or a truck on the highway shot from the side).

So yes, all CMOS-based cameras have this problem, but it is MUCH worse with DSLRs because of the line skipping: As I said, their resolution is much higher because of the still image function of these cameras. Therefore, there are simply more lines to be read out. Most of the lines are skipped when recording video, but that doesn’t mean that the remaining lines can be read out any faster than before. This results in even worse skew than with most other cameras. Link

Okay, but it's not the line skipping that's causing the problem, it's just compounding it. And it's not even really the line skipping, it's just the larger sensor (which requires line skipping).