Welcome to the megapixel race. We now have news that a mini version of the Sony Xperia Z1 is in the works, codenamed Xperia Z1 F, it will sport a smaller screen!
Let's be fair, the competition to deliver a pro spec smartphone camera is by all means a foregone conclusion. You will not be using all of it even if your social life depended on it. When you have 20.7 megapixels, the last thing you'd want to do is shoot images just for sharing on the web or Facebook. Pictures will have to scaled to fit and you probably down sample the image size just to fit your day to day social sharing requirement. If you don't. Just imaging what your data bills are going to be like when you start to upload each 10 megapixel JPEG images up to the cloud.
Now Sony thinks that you might not want a bigger 5 inch screen hence the Z1F is in the works and will sport the same 20.7 megapixel sensor. Still, I am not sure what you are going to do with the extra megapixels that you are not going to be using.
Print Size Chart
If all you are going to print are those 4R postcard size pictures, well I have good news for you. You don't even need 3 megapixels to get the job done. However if you are running for office and need election posters, then a larger image will be more appropriate.
Addicted to SizeAllow me to let you in on a secret. Pro Photogs love big pictures. The bigger the better. They sell this as posters and one off prints and there is no way around this unless you have loads of megapixels. It is also a norm in the industry where the photos are hacked off into smaller sizes due to cropping—to improve picture composition.
Apple's new iPhone is still 8 megapixels, which is fine if you shoot a tight crop in-camera as opposed to sectioning it off in a cropping spree. If you had 5 megapixels to play with, that's plenty enough for a desktop wallpaper on your retina display MacBook Pro.
Lessons for Newbie Smartphone PhotographersIf you are smartphone photographer taking pictures for an exhibition and need the megapixels, then go for the Xperia Z1. The smartphone has all you need to print an A3 sized poster and with careful doubling of the image size using image scaling software, you could increase the pixel count three times before the image starts to break.
Bear in mind that the pictures are still in JPG, which means that each time you 'resave' the image into another size, details will be lost. This is due to the compression algorithm used to make a file smaller. Once you have done this, rescaling it to a larger size will not work.