4K noisier than 1080p
After getting a Panasonic LX100 and discovering I couldn't easily stabilize most of my 4K/30fps handheld dollying and tracking shots in post the way I could with 1080p/60fps, I haven't been using the 4k much. But now I'm wanting to use it at least with locked down shots so I downscale it in a 1080p timeline as a lot of people are doing, and crop in and add very slow and smooth zooms without losing resolution, and I'm noticing another problem: yes, downscaled 4k is more detailed than 1080p, but it's also substantially noisier! Maybe grainier is a better term; I'm talking about the dancing grain you can see in a uniform, neutral area such as a wall. It doesn't look that bad, but it does mean it's quite noticeable if I intersperse 1080p and downscaled 4k shots, especially if I apply much cropping to the 4k.
So I'm just wondering if I'm doing something wrong with the settings, either in shooting or in post, or both. To get the best results mixing 1080p with 4k, do I need to, for example, max out the noise reduction settings when shooting 4k? Do I need to deliberately blur the 4k a bit when editing? Wouldn't doing those things take away the resolution advantage of 4k? Or should I not try to mix the two formats unless I have to? Seems strange that the 4k is what I'm trying to make look better, rather than the 1080p!
Hard to really answer this question without much more detail about your workflow such as camera settings, lens, lighting, codec etc. Generally speaking- apparent grain in any sort of footage is due to one or more of the following possible reasons: underexposure, excessive gain or simply a highly compressed camera codec that doesn't create a pristine signal. 4K is of course not specifically more or less susceptible to this than 1080p or SD would be. It's always going to be garbage in garbage out no matter the size of the frame- no offense meant.
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The LX100 is primarily a still camera. The still resolution is way too high for HD video. When shooting 1080p, they may use "pixel binning" to combine groups of adjacent pixels and down-rez to 1080. This might reduce noise as a side effect.
Also as Noah said, any codec difference between 4k and 1080 could play a factor. On the 5D Mark III people sometimes report more noise when using the ALL-I codec vs the IPB codec, even when both are used at 1080p/30.
I wouldn't say the LX100 is primarily a stills camera. It's basically a compact version of the hybrid, very video-friendly GH4, but a bit more stills oriented and without some of the more advanced video features. As with the GH4 and other hybrid mirrorless and DSLR cameras, I know that the full frame image is shrunk down using various techniques to make the much smaller 1080p image. Whereas with the 4K a smaller portion of the sensor is used and the 4k image is not shrunk down at all with the GH4, and only slightly with the LX100. I also know that using a smaller portion of the sensor will make any noise/grain appear larger, even if the resolution is higher.
But most people mixing 1080p and 4k on a 1080p timeline are using 1080p and 4K footage from exactly these types of cameras, and I haven't come across any complaints on the various forums about the 4k looking worse rather than better than the 1080p because of this enlarged noise/grain issue, even when cropping the 4k footage, so I assumed the noise/grain increase with the 4k was quite small. That's why I was surprised when the increase seemed pretty dramatic to me.
So I did some tests. I shot a scene at ISO 400 and then ISO 3200, which is about as high as you want to go with a micro four thirds sensor, correctly exposed and focused and keeping the exposure constant by changing shutter speed. First 1080p 60fps, using the "standard" profile and default settings. Then the exact same scene and lighting and exposure and ISOs using 4k 30fps, standard profile. First with default settings, then with everything at -5, then with everything at -5 except noise reduction at +5. Then I put the footage on a 1080p 30fps timeline in fcpx, with the 4k clips spatial conform setting at "none" and scaling set to 50%, so they fit the frame exactly. Some of the 1080p clips were deliberately zoomed in tighter so I could scale up the 4k clips to match the framing, and those 4k clips were scaled at 80%.
Now, since I was still at well under 100% for the 4K, I thought that even the 80% 4k shots should still look better than the 1080p. And I did find that at 400 ISO, all the 4k shots looked more detailed and generally better, even though at 80% I definitely noticed some significant grain/noise creeping in. But at 3200, while the image was still better overall at 50%, the increased grain was much more apparent, and with scaling up to 80% the noise was so much stronger that even though the detail was better I thought the image was worse over all. The 4k shots with everything dialed down to -5 looked best in every case, after I color corrected and in some cases put back in some sharpening, but with those 3200 ISO shots about the best I could do was add in a little gaussian blur to make the grain less apparent.
So is the lesson here simply that if I want my moderately cropped 4k to look better than my 1080p I need to either use a larger sensor or stay below 3200 ISO? Or are there some other settings I can use to decrease apparent grain in 4K? There are always denoisers like Neat Video, but I'm hoping not to have to resort to using those..
Isn't this just a question of physics? When you crop the image to 1080 you are only using a small section of the sensor. You are effectively using a smaller sensor. And we all know what small sensors are like for noise.
EDIT: I just noticed you suggested that as a cause.
[chris walker] "...most people mixing 1080p and 4k on a 1080p timeline are using 1080p and 4K footage from exactly these types of cameras, and I haven't come across any complaints on the various forums about the 4k looking worse rather than better than the 1080p because of this enlarged noise/grain issue, even when cropping the 4k footage, so I assumed the noise/grain increase with the 4k was quite small....are there some other settings I can use to decrease apparent grain in 4K? There are always denoisers like Neat Video, but I'm hoping not to have to resort to using those.."
I'm not sure casual reports from other users are a good indicator. Most of them did not do focused testing like you did at different ISOs. As you found, in a well-lit environment using lower ISOs there's less difference between 4k and 1080 noise (on a camera doing pixel binning at 1080). At higher ISOs the difference is more apparent.
This is similar noise behavior to a still camera if comparing native resolution and down-sized photos at low and high ISO. At low ISO there's not much noise so there's less difference between native and down-sized stills. At high ISO there's more noise so the down-sizing helps those stills but the native res stills don't benefit from that.
3200 ISO is pretty high for a m4/3 sensor. Even on my 5D3 I don't like going beyond 6400 shooting 1080p.
(1) Make sure you aren't using some in-camera setting which aggravates noise. Some flat exposure curves can worsen noise. I can't count the number of times I've seen 5D3 shooters say "All I did was use Cinestyle and ALL-I codec, now there's noise everywhere".
(2) In general if you "expose to the right" this may help.
(3) If your situation mandates low light, consider high-speed lenses such as the Voigtlander 25mm f/0.95 ($1k). If this seems expensive consider the f/0.7 Zeiss lens Stanley Kubrick used to shoot candle-lit scenes in Barry Lyndon cost $12 million (adjusted USD). http://www.bhphotovideo.com/c/product/1044065-REG/voigtlander_ba259m2_nokto...
(4) By all means consider noise processing such as Neat Video. IMO every clip of the final product should be meticulously post-processed, whether for color, exposure, stability, etc. Noise processing is just one more step of many. Here's a review of some: http://nofilmschool.com/2014/10/neat-video-vs-denoiser-ii-which-plug-better...
Thanks for the helpful advice Joe Marier.
Regarding camera settings aggravating noise, yes, I was using a setting that raised shadows and brought down highlights a little, and I'm going to test how much that is increasing my noise at high ISOs.
Regarding exposing to the right, that's really not an option with the LX100 which seems to have an overexposure bias and blows out highlights easily. Indeed, that's why I was using that setting that raised shadows and brought down highlights. I've been doing that in tandem with exposing a bit to the left, since blown highlights are much worse to me than noise. (Actually, I wanted a setting that only brought down highlights without raising shadows, but the LX100 doesn't have such a setting, unlike the GH4.)
Regarding low light imitations of the m43 sensor, that's never bothered me as much as inadequate dynamic range. ISO 3200 produces acceptable results for me with 1080p 60fps, and is all I need for almost all lighting situations I come across for my event work (mostly weddings) using a constant f2.8 zoom. When I can afford it, my next upgrade will be to sell my GH3, which I use now with 35-100 f2.8 zoom in tandem with the LX100, and get a GH4 along with a speed booster, a 50mm f1.4, and a 17-50mm f2.8 zoom. That way I'll have f1.0 when I need it, and be able to use 1600 ISO in the situations like wedding receptions where I'm having to use 3200 now. 1600 is substantially cleaner. Even thinking about using the BMPCC version of the speed booster, which would turn that f2.8 zoom into a ridiculously fast f1.7, while also getting rid of the extra crop factor you have with 4k on a GH4. Then I could shoot in 4K all the time and not worry about noise making it look worse rather than better than 1080p!
Regarding de-noisers, yes, I think I need to take the plunge. Going to read the article you linked to now..