[Xperia Z3 General] radicans:
20MP vs 8MP

I've been undecided about whether to shoot in 8MP or 20MP, as a general rule of thumb. So I got the idea to shoot something detailed in both 8MP and 20MP, identical settings, and compare. I wasn't in the mood (I'm sick as a dog) to spend ages to find the ideal test case, so I just used what happend to be in vicinity - a coaster made in cork and a juggling ball. No tripod, but I'm supported to a wall so it's as stable as it gets without a tripod :) While no sweeping conclusions can be made based on one scene, it's interesting nonetheless.

So I wanted to see how much more information is in the 20MP than in the 8MP. For this test I did three side by side comparisons:

1) The 20MP photo, next to a scaled up version of the corresponding 8MP photo with some sharpening filter applied. The idea here is that if you can make a 8MP photo look like a 20MP photo, then there really is no more information in the 20MP photo. I'm allowing processing since the Z3 photos as we all know are heavily processed. For all we know, the 20MP could be an upsized 8MP image (though I'm definitely not saying it is).

2) The 8MP photo next to a downsized (to 8MP) version of the 20MP photo.

3) The 20MP photo scaled down to 8MP, the scaled back up again to 20MP!

Note, all the image resizing is done by me in GIMP (free image manipulation software, I do recommend it! http://www.gimp.org), nothing is resized in camera.

To make it more exciting, the photos are mixed up. Can you tell which one is which? ;)

The answer is hidden below the photo. The embedded photo is just for show, use the dropbox one if you want to look closer, as the imgur becomes slightly compressed and the already small differences are dimished further. All images are 1:1 crops.

https://db.tt/5WNAgetL (ABCD, for comparison 1) and 2) )

https://db.tt/X3IiVbqW (EF, for comparison 3) )

A: 20MP original

B: 8MP scaled up to 20MP plus sharpening.

C: 8MP original

D: 20MP downsized to 8MP

E: 20MP downsized to 8MP, upsized to 20MP (using sinc (lanczos3) scaling algorithm in GIMP)

F: 20MP original

Looking at A and B I would say there is somewhat more information in the original 20MP photo (A), compared with the scaled up version, thankfully! But it sure ain't much, definitely not 2.5x more information, when judged visually (and subjectively).

In photos C and D I would say D looks better, i.e. the downsized version of the 20MP image, but not by much. But you can see some fine detail there which isn't in the slightly softer 8MP original image (C).

But what is really interesting is that there is virtually no difference between E and F! This implies that even though the 20MP photo has more detail than the 8MP photo, there is not more information in the 20MP photo, than what can be contained in a 8MP image!

So, ideally one would like to have the camera take a photo in 20MP, then scale it down to 8MP and save that. I think this is what Sony claims that they are doing (maybe only in superior auto?) for the 8MP mode, but if it were so the scaled down version of my 20MP photo should not have looked better than the 8MP photo. Maybe they are using a fast downsizing algorithm which is not that good. After all, the Sinc downscaling is quite slow compared to linear and cubic interpolation.

Anyway, make of it what you want. It's just an observation based on one photo. The results will most likely be somewhat different for a different scene.

Originals:

https://db.tt/a4n48Ji9

https://db.tt/Kfaye3Wu