More pixels are better for noise reduction. Really?

Started May 8, 2015 | Discussions thread
CreeDo Senior Member • Posts: 1,619
Sounds about right (some noise reduced samples)
2

I think I've been overestimating the value of downsampling (pixel binning I guess) to reduce noise... so in a sense the OP is right, you don't buy a 36 megapixel camera thinking "my shots will look just as clean as a 16 megapixel camera, as long as I shrink the image to the same size".

But I can see you're right, that it's all about the noise reduction algorithms, and with good NR you can get the full value of the noisier, higher resolution sensor... getting a result that is definitely better than an untouched shot from the 16mp sensor, and arguably better than a noise-reduced shot from that sensor.

I did a little comparison of how these look after NR.
DXO's prime is, to me, unquestionably the best for this.
So I ran both raws through it, with no adjustments except to make the white balance match.

I left color noise reduction at 100. This is the DXO default and AFAICT is totally safe.
I did luminance NR at varying levels -

30 (10 below default)
50 (10 above default)
70 (30 above default)

After stacking these in photoshop and then turning layers on and off, it looked to me like there was no downside to using the most aggressive of these options... the shot with 70 noise reduction just looked cleaner than the shots with 30 and 50 NR, without losing any details.

So the below is a comparison of the d4s at ISO 6400, vs. a shrunk d810 shot with noise reduction, and finally a d4s shot with identical noise reduction.

To me, the d800 results look best, giving the best balance of noise and detail, and if I hadn't shrunk the d800 shots I know they'd have even more detail and would make for larger prints. Though you could argue the d4s shots look better in other ways, notably color saturation.

If there is any downside to heavy noise reduction with DXO, it might show up here... the gray-on-gray DPreview logo text seems a little softer, with maybe slightly rounded corners on the capital letters, vs. the untouched noisy shot. And some of the "digital photography review" text seems to fade away. The small text though is surprisingly clean in the NR'd shots, in the white block I can barely read the line that starts with "parts of our earth" and I think it's maybe a smidge easier to make out in the d810 shot.

Here's one area where the d4s arguably is better, unless this is just a white balance issue or something. The d4s colors are clearly more saturated and probably more accurate to what the naked eye sees. It might be a 'picture style' issue, meaning the d4s may have a saturation setting that you can change within the camera, and it's set higher than the d810's equivalent setting. But I suspect the d810's colors come out "watered down" as a side effect of high ISO.

This image shows the difference it makes, having a little extra detail to start with before shrinking the d810 image down to d4s size. The cards look a little crisper, and the text on the color wheel is noticeably cleaner, especially in the green and blue areas. Check out the top right corner of the feathers, which look sharper in the d810 shot, and I think the brillo pad's rough texture shows up better in the d810 shot also. Another small bonus, you can see the d810 AA filter is apparently better than the d4s, or else this is a side effect of the higher resolution. Look at the hair on the Jack of Hearts - the d800 shows the thin lines in the hair, the d4s has some moire effect that causes them to be lost under a pattern of horizontal lines that don't exist in the card artwork. You can also see it on the thin inner border of the card to the right, where there are several parallel lines.

In the darker areas, these's still visible blotchy noise. It also appears that the d4s exposed the very dark areas a smidge better, like the black paint tube is a bit more distinct from the background, but that seems trivial. The d810 shows cleaner text on the tubes, check out the words "brilliant red" and "lemon yellow". The d4s is still showing more saturation, especially in the red brush and the bottom yellow paint tube.

Anyway, based on the results of aggressive noise reduction, I'd rather have a d800 than a d4s. Well, ok, I'd rather have a d4s and then I'd sell it and get a d800, and pocket the extra $3,000.

 CreeDo's gear list:CreeDo's gear list
Canon EOS 7D Mark II Canon EF 400mm f/5.6L USM Canon EF-S 60mm f/2.8 Macro USM Canon EF 70-200mm F2.8L IS II USM Rokinon 14mm F2.8 IF ED MC +4 more
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