Sunday, 3 April 2011

Hacked GH1 vs GH2: Video quality comparison

A matter of some dispute is which camera gives the best video quality: The hacked GH1 or the newer GH2.

The GH1 has earned some popularity due to the possibility to change the firmware. Adjusting the firmware is generally referred to as "hacking" the camera. There are many options, and the most useful ones are the possibility to get native 1080p 25fps (with the PAL version), and to increase the bitrate. I have done both with my GH1.

I've compared them before, and my conclusion back then was that the GH2 had better auto white balance (AWB) for indoor lightning, but other than that, it was hard to find much evidence of better video quality. I was advised that I should try to pan the cameras while recording foliage.

There are two problems with that: One is that there is no foliage in Scandinavia at this time, since spring is not yet here. The other is: How would I know that I have panned at the same speed, giving comparable footage?

For the second problem, Technic LEGO again comes to the rescue. Previously, I made a rotating object using Technic LEGO, and video recorded that. This time, I made a platform for the camera out of Technic LEGO, and used that to pan the cameras at the same speed. Here is how the platform works:



Putting the platform outdoors enabled me to record the same footage using both cameras. I used the same image parameters for both cameras: ISO 200, f/3.2, 1/400s shutter speed, outdoor sunny white balance, manual focus. Due to limitations in the cameras, I could not use the same frame per second count. I used 1080p for both, but 25fps for the GH1 and 24fps for the GH2.

I used the Lumix G 14mm f/2.5 lens, which is more than sharp enough for this test.

In real life use, one would not normally use a shutter speed of 1/400s. The normal speed to use is twice that of the framerate, which is 1/50s in my case. This is called a 180° shutter, since it is open half the time on average.

One reason why a 180° shutter is normally used, is to get motion blurring for objects moving across the frame. Without motion blurring, the movement can look unnatural on film, since the object will appear as if it materializes in different spots at different times. This is confusing for the person watching. I have a discussion about this, and the need for Neutral Density (ND) filters here.

In my case, though, I want to avoid motion blurring. The whole point of the experiment is to see which camera resolves the most details, and then I must make sure that the video stream contains as much details as possible to begin with. Motion blurring typically makes the footage softer.

Due to the hacked GH1 having a higher bitrate, it generated larger video files. The GH1 gave 5.4 MB/s, while the GH2 gave 2.8 MB/s.

Here are the two video recordings:



GH1



GH2

It's somewhat difficult to evaluate the quality of the video by looking at the videos, especially since YouTube compresses them anyway. So to aid in comparing them, I have grabbed single frames from them to compare.

Here are two similar frames (click for larger versions of them):


GH1


GH2

The first thing we can see, is that the GH1 still image is brighter, despite having the same image parameters. I interpret this to mean that the ISO scales of the cameras are not the same: The GH1 ISO scale corresponds to higher ISO values with the GH2. It is a well known and documented fact that the GH1 ISO scale is generous, meaning that a given ISO value gives more sensitivity than the same value for comparable cameras. The GH2 ISO scale is more normalized.

Another thing we can note, is that the trees lean a bit to the right. This is due to panning the camera, and the rolling shutter. I've evaluated the rolling shutter effects of the two cameras before, and found them to be comparable. Rolling shutter can create artifacts when using both the GH1 and GH2, but for normal use, it is not a real problem.

Here are direct comparisons between two areas from the two video streams. They are shown here in 100%, i.e., not rescaled and not sharpened.


Since the exposure is slightly different, I have also done an autolevels on the images, to make them comparable. Here they are:


Conclusion

One could be tempted to think that the GH1 gives better video quality, due to the twice as high video bitrate. But the GH2 has other advances. We don't know for sure just how the GH2 handles the video compared with the GH1, but it is reasonable to guess that it samples more pixels as a basis for the video output, and that the compression algorithm is better.

So, which video stream is better in my test? I think they are quite similar. Perhaps one can conclude that the GH2 gives somewhat better contrast and sharpness. The GH1 has slightly washed out colours, I think. But the difference is small.

My conclusion so far is that the GH2, even with lower bitrate, gives slightly better video quality. But both cameras are very competent.

13 comments:

  1. Indeed in a blind test there is no way to distinguish the equipment used.
    Thanks a lot for Your evaluation.

    PS
    My GH2 has just arrived!

    ReplyDelete
  2. Shooting a trumpet chart with a Vivitar 90mm 2.5 macro, the GH13 with the Blackout-Powell 24p edges out the GH2. In the real world, they are very close, each has advantages. Foliage looks a tad better on the GH2 but subtle motion is better on the GH13. The real advantage to the GH2 is the perks--ETC mode, peaking, HDMI monitoring.

    ReplyDelete
  3. Your test is quite nice, thanks for it, at ISO 200 there isn't much difference, however at higher ISOs 2 things happens:
    - GH1 ISO set value is lower than the reality, GH2 is more conservative (you stated that GH1 was more conservative, when in fact sensitivity of GH1 at ISO 800 is almost equivalent to ISO 1600 on a Canon)
    - GH2 has less banding at higher ISOs, but it needs to have ISO differences in consideration to do a proper evaluation = same shutter speed and lens aperture, letting ISO to 'float'

    With that said, I totally agree with your conclusions (even though I own a GH1) GH2 is slightly better in video quality, not to mention that it has some extra features (audio recording volume control, HDMI out during recording, ETC) :]

    ReplyDelete
  4. When I said the GH1 has a more conservative ISO scale, I meant that it corresponds to higher ISO values with comparable cameras. I can see that the word "conservative" can be misunderstood, so I'll try to change the wording.

    The GH2 is a much better camera overall. Perhaps the only thing I miss from the GH1 is the rubberized finish, which felt safer to handle.

    ReplyDelete
  5. What about posterization in GH2? Are you investigate about this?

    ReplyDelete
  6. Would you be interested in posting on your blog a review that I could make on the Olympus 14-54 2.8~3.5 and possibly the Sigma 105 2.8 macro?

    Email me at pipblackpower@gmail.com if you're interested so we can discuss test methodologies!

    Cheers for the great blog!

    ReplyDelete
  7. Thanks for your suggestion. At the moment, I prefer to write the articles myself. But I would suggest that you post your review on the Micro Four Thirds forum on dpreview.com. That is probably the most read Micro Four Thirds related forum in the world, so it will get a lot of comments for your review.

    ReplyDelete
  8. I think I expressed myself wrongly. I wouldn't be interested in writing the review myself, what I would like to do is provide only the material, like samples at same focal legnth from several lenses and perhaps contribute a small part only regarding weight and ergonomics.

    Just drop me a email if you're interested.

    ReplyDelete
  9. Thanks for the comparision. One thing I'm trying to research is, video quality aside, how do the two compare for picture quality?

    It seems like all the comparisons between the GH1 hacked vs. GH2 is video quality only.

    ReplyDelete
  10. For a picture quality comparison, I would recommend that you look at the reviews by DPREVIEW.COM. They have reviewed both, and have standard picture quality comparison images.

    ReplyDelete
  11. When I shoot in 1080i PAL on my hacked GH2,
    there is motion blur.

    Motion blur can't be seen on LCD, only
    on computer.

    How to convert 1080i to 720 X 576 without blur?

    Many thanks!
    aaronmgoodman@gmail.com

    ReplyDelete
  12. Hey eager stuff precise substance your response on
    compare them here

    ReplyDelete