GH2 Image noise or defective sensor?

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kevhayes2010

Member
First of all, sorry for what would appear to be a duplicate thread. I know a number of people have posted similar concerns regarding image noise and/or pixel refresh problems specifically related to video. I haven't found any resolution to the existing posts or to the unique problem I seem to be having so thought I would post here anyway looking for advice.

The problem I have is related to long exposure on stills. I am seeing what would appear to be a very specific pattern of bright pixels / groups of pixels (as shown in the images below) that seem to be independent of regular ISO related noise. In the sample images I've provided you can see a base level of noise throughout the image which is totally acceptable and between images this noise is of a consistent intensity but of a differing pattern (as you would expect). The bright pixels I cannot explain and are of a fixed pattern and intensity - they are exactly the same between different images.

I was basically attempting to do some time-lapse photography from dusk through to night with the camera controlling shutter speed and me the aperture and ISO. I noticed this additional 'bright' noise creeping into the image around 8 or 10 second long exposures so I brought my camera inside to do some controlled tests with a manual exposure of a consistent 15 seconds at ISO 800 and an aperture of 3.5 (using the 14 -42 kit lens). I also tried ISO 160 at 30 seconds and an aperture of 22 which yielded the same results. The same is also true with the 20mm pancake lens. I also tried the same exposures with the lens cap on, where I would expect to see only conventional image noise, but the bright spots are still there.

The regular noise I can deal with, but I am concerned this is not typical behaviour for this camera and that I might have a defective sensor. As Im sure you can understand, this type of bright noise is very degrading for imagery of the night sky... I tried long exposure noise reduction and that eliminates some of the bright spots, but also starts to damage the integrity of the original image. I also tried performing both a pixel refresh and a sensor clean to no avail.

The colour profile I was using was -2 -2 -2 +1 (Smooth) which would seem to be the recommendations on this forum?)

All the images below are roughly a quarter crop from the originals.

Interior crop first shot
Noise_01.jpg


Interior crop second shot
Noise_02.jpg


lens cap on first shot
Noise_03.jpg


lens cap on second shot
Noise_04.jpg


Black and white, exaggerated contrast
Noise_05.jpg



So, do I have a defective sensor or am I going about this the wrong way?
 
Have you tried taking a control picture with a different lens or without lens attached? This noise pattern looks very weird...
 
There's a menu setting called "Long Exposure NR", which adds a special noise reduction with, you guessed it, long exposures. Make sure that is set to "on" and try another test.
 
I tried with both the kit lens and the 20mm pancake lens and the same bright noise pattern is apparent in both. Also, the second pair of images above shows the kit lens with the lens cap on. I haven't tried this with no lens attached...
 
I tried with the long exposure noise reduction (as indicated in my original post) and this does eliminate some of the unusual noise but not all. I also found this to be slightly degrading to the overall image quality introducing banding in areas of low contrast.
 
In my opinion, long exposure noise reduction has a limited threshold of usefulness as it consumes as much time to process as the image took to capture. At 15 seconds this is just about acceptable (resulting in a 30 second long 'capture time') but if I wish to go to 30 seconds or, dare I say it, a bulb exposure of > 30 seconds this would not be realistic for a time-lapse sequence.

I am also aware of the technique of capturing a single frame with the lens cap on at the same exposure and using this to negate the effect of the fixed pattern noise in the resulting images but this would have to be performed frame by frame to get the best results and for a sequence of a few hundred frames this is not acceptable.

I have done time-lapse sequences using other cameras - notably the 7D - and although I would not dare compare that specific camera to the video quality of the GH2, I did not encounter this kind of problem with long exposures on still images.

To quote myself, the conventional noise seen in both video and stills up to and including ISO 3200 is fine and in some situations desirable if you are going for a specific look - I can live with this just fine. At a decent shutter speed when hand held or even on a tripod to dip into exposures of around 1 second, the base noise apparent in the images is quite nice. But this in my opinion is something else... and I would not expect to see it so apparent at 160 ISO (not shown above but at a 30 second exposure is there just as bad)
 
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Honestly I never try a long expose timelaps before ( normally I have max 1 or 2 sec) without a long exposure on any camerea before, but I agree it look odd for me too.

But I disagree that you could not use the blackframe even in a timelaps as a corection.

At the moment I am not shure if the GH2 has some blackcalibration in one of the menues like other professional videocams eg red or AF 100.

Anyhow maybe some other guys can try it with their GH2. If I have time I will do it next week.

Again I dont see this too with our Canon timelaps before. But As I told we was always below 2 sec exposure.
 
Yeah, its not there on shorter exposures - or at least considerably less noticeable. At ISO 800 up to 3200 you can see the regular ISO related noise which is completely acceptable, but this noise is something else I am sure and kicks in at longer exposures. It doesn't have the same visual properties of typical sensor noise in my opinion.

Id appreciate some comparisons - that would be a great help in debugging whether or not this is just my camera or not. I'm just worried this is a manufacturing fault in my camera alone at this point.

ISO 800, aperture of around 3.5 and 15 second exposure. -2 -2 -2 +1 (Smooth) colour profile, preferably with kit lens or 20mm pancake.

or

ISO 160, aperture of around 3.5 and 30 second exposure. -2 -2 -2 +1 (Smooth) colour profile, preferably with kit lens or 20mm pancake.

Obviously, both at night / low light / no direct light, only ambient (as this was originally for time-lapse through dusk into night)

Thanks!
 
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Now that I think of it, I did some long exposures at night on the GH1 in the summer of 2009 when I first got mine. It had the same problem you are showing but not quite as severe. I think I put it out of my mind because I was disappointed. Out of curiosity, are you shooting JPEG or Raw. Maybe when shooting Raw, this problem could be fixed? Or won't show up?
 
Ok, I just tried this on my GH13 with lens cap on. ISO160 at 30sec with and without Long Shutter NR. Without the NR I get exactly the same noise you are seeing (maybe a little less of it though). Using Silkypix, however, I could get rid of most it by setting: False color ctrl to 100; Neat Noise to 100; Noise reduction to 0; Noise level to 100; Noise cancel to 100; All sharpness set to 0. I don't know how useful that would be with an actual photo but I have found Silkypix to have excellent noise handling algorithms.
 
Thanks guys for your suggestions and tests. Having owned a GH1(3) and recently upgraded to a GH2 I was hoping the new sensor would have eliminated issues like this. I appreciate that there are work-arounds to resolve some of the problem, but this would equate to a huge amount of extra time to manually process each frame (as either Raw or Jpeg) for a 150 + frame time-lapse.

I managed to get slightly better results at ISO 160 and a 30 second exposure with regular noise reduction at -2, but this is still not ideal. I am reluctant to go near the long exposure noise reduction at this length of exposure as 1 frame would take 60 seconds to capture (30 second exposure and 30 second process) which would mean only 60 images per hour which is going to give a much more 'choppy' time-lapse sequence...
 
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