By Werner Ruotsalainen on Wed, 02/29/2012
Let me continue (previous article HERE) with the systematic test of the Nokia PureView 808, Nokia's new cameraphone flagship model, which, based on my tests and measurements so far, will be even bigger a hit than the Nokia N95 was back in the day. (Just to remember: back in its day, the N95 had by far the best camera among all mobile phones.)
In this current installment, I try to provide you with answers to
- the high ISO behaviour in both full-resolution and binned mode
- whether the downsampling helps at keeping absolute resolution high; that is, is the (binned) image quality, detail-wise, comparable to those of the Foveon sensors
- how the image sharpness compares to the Panasonic ZS3/TZ7, which is one of the 10 Mpixel P&S cameras that have the sharpest glass (=lens) - no wonder it has won DPReview's group test.
Vs. the Panasonic ZS3/TZ7
Let's start with an quiz. Which of the following two shot crops (click on them to see the full-resolution one! Don't try judging using just the thumbnails!) has been taken by the, lens sharpness-wise, absolutely great 10 Mpixel Panasonic ZS3/TZ7, and which with the 5Mpixel binned mode of the PureView 808? (After the two crops, scroll down a bit so that you can see the answer / the rest of the article!)
(several linebreaks to hide the answer - scroll down!)
You'd certainly expect the ZS3 to be the bottom one – after all, the text is completely readable, including the “R” sign on the “Bon Bum” on it, and it has two times the resolution of the 808 – and, after all, its lens is really-really good and sharp.
Well, you're completely wrong. The top one is the ZS3. As you can see, the binned mode (of the PureView 808) indeed delivers way better results at significantly lower (target) resolutions than native, non-binned sensors (here, the Panasonic ZS3/TZ7). However much the Panasonic model has a very sharp lens, coupled together with double the resolution, it simply can't hold a candle to the binned 808. The latter is way-way sharper.
(The original shot made by the ZS3 is HERE. If you check out the EXIF data, you'll see it's shot at ISO 80 (f: 3.3, 25mm equiv., 1/40 sec). That is, at the most ideal, lowest ISO.)
Resolution in binned mode
If you know a little bit about Bayer sensors (the sensors used in all current cameras except for Sigma's high-end ones), you may well know that no matter how sharp a lens you use, you will never be able to produce as much detail as the total pixel number of the sensor would deliver. The reason for this is simple: a 10 Mpixel sensor is really only about a 3.3 Mpixel one when individual target pixels are concerned. (See THIS for more info.) This is why the 5 Mpixel binned mode delivered far superior results to the Bayer sensor-based ZS3.
Let's compare how the effective sharpness is affected when you use a lower-resolution (binned) mode instead of the full-resolution one. The following crops speak for themselves (again, try reading the text on the cookies, compare the readability of the “R” sign etc): (as usual, do click on the thumbnails for the original versions):
(I don't provide a 3 Mpixel – at least not now – crop as it was only at the hotel that I noticed the base ISO shot was, for some reason, bad. See the high ISO section on info on the true resolution – even at ISO 1600!)
As you can see, the full-resolution image still delivers superior detail resolution, even compared to the 8 Mpixel shot. Compare, for example, the “R” (trademark sign) after “TM/” on the brown cookie (bottom right). On the two binned shots, it's very hard to see it's indeed an “R” and not a “P” in a circle. That is, no matter how much true resolution binned images have (compared to any other cameras, as we've seen the previous section when compared to the ZS3 – except for that of Sigma, of course), the full-resolution ones will still have more.
I've also shot exactly the same series in ISO 1600 – the highest sensitivity that can be used on the PureView. (The previous shots have all been shot at ISO 80 – I used manual ISO.) As you can see in the following screenshots, there's almost no additional noise reduction applied. (The final version of the firmware will surely add something like this.) This means the high-ISO images will be almost as detailed as the low-ISO ones and there's no software-based smearing to clean up the noise. With plenty of additional noise – of course. It's also worth noticing that there is practically no additional difference between the noise level of the binned and the non-binned (original-resolution) shots, apart from the usual noise reduction delivered by subsampling. That is, nothing magical happens: the “binned” pixels don't magically become a pixel similar to, say, those of cameras using Sony's latest APS-C CMOS (used in the latest Pentax, Nikon and Sony cameras; for example, the NEX-5n), the absolute noise king of all. (Of course, assuming the same sensor area and number of effective pixels, an APS-C-sized Bayer sensor will never be able to deliver such an effective, real resolution as that of the Nokia. That is, while the binned 808 is definitely more noisy than a native Bayer sensor with native pixels, it also delivers much better resolution. It, therefore, can't be stated “the 808's sensor is a loser because it doesn't deliver as clean, noise-free results as the NEX-5n in binned mode”.)
Note that the 8Mp and 5Mp shots' screenshots aren't very good; I only provide them to assess the noise, not the detail / sharpness. (As I was not allowed to transfer the PureView shots to my devices via Bluetooth, I had to rely on making photos of the screen under as controlled an environment as I could provide. This is a perfectly usable approach when assessing noise and resolution – but, of course, not dynamic range and some other stuff. When straight shooting screens, problems inevitably occur, which may become only visible hours after finishing shooting, when starting to evaluate the shots on a desktop computer.) As opposed to the ISO80 case, however, the 3 Mpixel shot's copy was successful; with it, you'll want to check out both noise (as with the 8/5 Mpixel shots) and the detail (unlike with the 8/5 Mpixel shots).
(8 Mpixel - again, only assess the noise level, NOT the detail / blurriness!)
(5 Mpixel - again, only assess the noise level, NOT the detail / blurriness!)
Also note that these shots have been shot under exactly the same circumstances than the ISO80 ones.
All in all,
The camera in the 808 is absolutely gorgeous in the resolution department. Binned shots (the ones the camera takes by default) contain way more detail than other (Bayer) cameras with two or even three times more pixels. The noise, as expected, is pretty high at ISO 1600, but in binned (=subsampled) mode it's drastically reduced, while not smearing away any detail. Congratulations, Nokia!