Monday, 20 December 2010

GH1 vs GH2: Rolling shutter evaluation

Rolling shutter is the name of a type of mechanical or electronical shutter mechanism. In this type of shutter, the whole film or sensor is not exposed exactly at once, but rather, a shutter rolls across the frame and exposes it bit for bit. Rolling shutter is also the name of the distortion associated with this shutter implementation.

You can see this distortion for example when panning heavily during video recording. It looks like the scenery is "leaning" towards one side when panning. I tried the Samsung NX10, and immediately noticed that the viewfinder had much more rolling shutter artifacts than the Panasonic G-series.

This shutter implementation also leads to distortion to rotating elements. To test which camera has the most rolling shutter artifacts out of the Panasonic GH1 and GH2, I made a simple LEGO contraption which rotates a propeller at a constant speed. Then I videofilmed this with both cameras, using the Olympus 50mm f/2 lens.

Here are the two video streams:



GH1, ISO 1600, f/2, 1/500 second, 25p, 1080



GH2, ISO 3200, f/2, 1/1000 second, 24p, 1080

To more easily compare the rolling shutter artifacts, I have made similar framegrabs from both:


What we see here, is that the distortion is slightly smaller in the GH2 video stream. The shorter the distance between the two prongs to the left, the more the distortion.

So my conclusion is that the GH2 handles rolling shutter at least as good as the GH1.

For real life usage, rolling shutter is not a problem with GH1 or GH2 video. You can generate these effects by filming a rotating propeller, like I did here. Or by panning heavily. But most types of video footage will not display any noticeable rolling shutter artifacts.

As a side note, the amount of rolling shutter artifacts depend on the speed of the rolling shutter (in a mechanical implementation), or the speed of the sequential image data readout for a digital shutter. It does not depend on the shutter speed itself. Here is an illustration, where you can see three different shutter speeds generating the same amount of rolling shutter artifacts. But the amount of motion blurring is of course different.


Another term widely used is global shutter. This refers to a system in which the exposure values from the sensor are read all at once. Since the values are not read out sequentially, there are no rolling shutter artifacts with a perfect global shutter.

Before launching the GH2, a Panasonic representative was quoted saying that implementing a global shutter in Micro Four Thirds cameras is not coming soon: At the very earliest with the GH3. In retrospect, the the Panasonic GH3 did not introduce global shutter. And now, it looks like the GH4 (aka GH4K) is going to be more about 4K video than global shutter.

9 comments:

  1. Is rolling shutter a big problem in real life situations? How do You handle this? What should I keep in mind during filming? Last year I hoped that GH2 would have global shutter implemented but unfortunatelly it has not happened... Waiting for GH3 or GH4 with global shutter has no sense due to waste of time and opportunities so I'm going to buy GH2 when it is available in my country, but Your comments on this issue in real life situations will be of great value for me.

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  2. Good question.

    I would say the answer is really simple: Rolling shutter is not a problem in real life use with the GH1 or GH2.

    You can generate noticeable rolling shutter artifacts by panning quickly horizontally (left or right). However, such footage is not very usable anyway. Normally, you will not want to record while panning quickly.

    So the conclusion is: When using the GH1 or GH2, don't worry about rolling shutter artifacts.

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  3. Ufff... good to know that! Thanks!

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  4. Since rolling shutter can be more pronounced at slower shutter speeds, really you should test the two cameras with the same shutter speeds.

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  5. The rolling shutter artifacts depend on the shutter curtain speed, not the shutter speed itself. So your suggestion does not make sense.

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  6. Hi,
    Is possible to get Ultra slow Motion Video with the GH1?
    I was amazed because of a Casio FC100 that can take ultra slow motion video(Search for slow motion 1000fps Casio EX-FC100 in Youtube).

    Is it possible to make something like that with our GH1?

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  7. To my knowledge, no. Ultra slow motion is not possible.

    The European version of the GH1 can record in 50fps, and you can slow that down to 25fps, say, for 50% slow motion. But that is nowhere near ultra slow motion.

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  8. Rolling shutter is caused also by vibrations,
    If you take a camera up in the air with a rc remote helicopter, the vibrations caused by the engine produces the "jello" effect, distortions making the video looking like dancing waves.

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  9. Yes, I agree, that is also a type of rolling shutter effect. It is also caused by movements while the shutter is exposed.

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