The meaning of Megapixels in smartphones

Irish Stones

I am a bit confused about the meaning of MP for cameras in smartphones.

I have a reflex digital camera with a 24 MP sensor, which gives me photos of 6000*4000 pixels, up to 12 MB in size, and this is exactly what I would expect from a sensor like that.

All the smartphones I had so far would say they had 20 MP, or 80 MP, even 108 MP, like the one I currently have. As for this last one, it was advertised as a very good camera phone, with so many pixels to give back wonderful photos. Nonetheless, the photos I take with those smartphones are small sized, both in file size and in MP. For instance, one of the last photos I took with my phone is 4000*1800 pixels (equals to 7.2 MP), file size 1.9 MB. And the quality, well, quite disappointing.

Where have the other 101 MP gone? Can you help me understand? Thanks!

blackbox

File compression - I'm assuming your picture files are in jpg format.

If done right, this shouldn't really affect picture quality that much.

The part of a camera that has the most impact on picture quality is the lens.

Irish Stones

https://www.boards.ie/discussion/comment/119683353#Comment_119683353

A compressed file should still have the full MP, shouldn't it?

You can have a not compressed 108 MP photo (with excellent details and huge file size), and a highly compressed 108 MP photo (with very poor details and small file size).

I also thought the very high number of MP in my phone was for the digital zoom, so that the camera could zoom in 6x and still have a good resolution photo. The reality is that if I take a photo with the zoom at 1x, the photo is rather good, but gets blurred if I zoom in on the display. If I take a photo with the zoom at 2x, the photo is still the same file size, but the details are gone. So, it doesn't seem that those MP are being really used.

FYI, my current phone is a Redmi Note 11 Pro 5G. Thanks.

blackbox

https://www.boards.ie/discussion/comment/119683387#Comment_119683387

For a sensor 4000x1800 there are 7.2 Megapixels. For each pixel there is data on colour and brightness. This probably uses 24 bits per pixel so it results in a raw file size larger than 7,2MB. Your SLR camera will have the option to save RAW files.

File compression is a complex area, but for simplicity imagine there are 200 black pixels together. Rather than saving the same information 200 times, the file compression software saves this as 200 x black, which takes a lot less space.

Further compression will combine information on pixels that are close to the same and this is when you start to get quality losses.

See Wikipedia for further info - https://en.wikipedia.org/wiki/JPEG

Flinty997

This is the review of the camera of that phone...

https://m.gsmarena.com/xiaomi_redmi_note_11_pro_5g-review-2390p5.php

Phones generally resample (shrink using a formula) the image from the sensor to a smaller size in this case down to 12mp as it improves the quality of the picture. You can probably go into a manual mode and shoot the full resolution but the result won't be as good. The idea would be to process it afterwards in a computer or something.

The large pixel count allows you to crop the photo and still get a decent size for printing or resampling afterwards. Not zooming.

Any digital zoom simply fakes the effect of real zoom and you should avoid ever going it.

Lastly that phone lacks OIS (optical image stabilization) which gives you a much sharper image. Digital stabilization fakes this and isn't anything like as good. You end up with more out of focus photos.

Someone here has the Xiaomi 10 T Pro which is similar to your phone camera (108mp) but has OIS and the pictures are really good out if it. But as that review says there are minor differences between the zillion of Xiaomi models and some are better than others, especially with regard to the camera performance.

Flinty997

If you are buying a phone and want a decent camera check out the better review sites to see their opinion on the camera. That gsm arena does detailed camera reviews.

Higher pixel count does not always mean better quality photos. That's a marketing trick.

Irish Stones

https://www.boards.ie/discussion/comment/119683551#Comment_119683551

I looked into all settings I could find and I couldn't see any item that would allow me to use the full resolution of the sensor. So I really don't understand the use of so many pixels if they are never used.

I thought that the huge pixel count would allow me to crop an image while retaining a certain quality, but this is not the case with my phone. If I crop a photo that I take with the zoom at 1x, I will get a blurred and grainy photo. It wouldn't happen if the photo had the full 108 MP and I crop it 50%, and I would still expect a 54 MP.

So rather than the output quality, the issue here is why do these phones have billions of pixels, then the photos have so few pixels in the file.

Irish Stones

https://www.boards.ie/discussion/comment/119683579#Comment_119683579

Yes, but anyway those pixels maybe don't even exist if my photos are 7.2 MP.

Flinty997

On the Xiaomi phone we have in Photo mode choose "more" there is a button for 108 and its takes a 108mp photo.

Flinty997

I think you missing the point of resampling. 99.9% of people don't mess with the settings.

Irish Stones

https://www.boards.ie/discussion/comment/119684934#Comment_119684934

Thanks so much, I don't know how I missed it! 😲

I took a photo in 108 Mp mode, and it's 108 Mp, but strangely the photo is only 8.5 MB.

The other con is that the photo is only in 4:3 aspect ratio, and it can only be zoomed in 2x. But I guess that cropping in any image editor should help.

https://www.boards.ie/discussion/comment/119684947#Comment_119684947

Not sure I have understood this.

ohnonotgmail

Take a read of this. the sensor in your camera is much bigger than the sensor in your phone. Bigger sensor = better pictures.

https://thesmartphonephotographer.com/truth-about-phone-megapixels/#:~:text=Mobile%20camera%20MP%20vs.&text=A%20typical%20full%2Dframe%20DSLR,that%20of%20a%20smartphone%20sensor.

Flinty997

https://www.boards.ie/discussion/comment/119694700#Comment_119694700

Images look better when they are shrunk.

So that's a trick phones use to improve their photos.

Most people aren't going to edit their photos after they are taken. So will never use the unshrunk photo.

The image is that size because its compressed. Unshrunk and uncompressed is considered a raw photo. Only some phones and cameras will give you the option of shooting in raw mode. All profession gear will though.

5uspect

It's all marketing.

The sensor in your dSLR is much bigger than the tiny thing in a smartphone. A 10MP dSLR will take much cleaner images than a 50MP phone because you get more light per pixel. A good quality (bulky) lens will resolve detail better also compared to the tiny thing in a smartphone.

So while a phone will be advertised with a massive pixel count in many situations the pixels will be binned so that each 2x2, 3x3 or 5x5 pixel groups act as one pixel. This helps reduce the noice that is associated with small sensors with a high pixel count. This binning is essentially what the 48 MP camera in the new iPhone is doing, binning 2x2 gives you a 12MP image. Averaging the signal across the four pixels reduced noise. If you want to get the 48MP image you need to shoot in RAW or use an app that allows it.

There is also a lot computational photography going on in these phones to remove noise, sharpen, merge to HDR etc. Some even upscale with AI to add information that wasn't there.

Ultimately MP is nothing without a lens that can resolve the detail to match.

cnocbui

https://www.boards.ie/discussion/comment/119684628#Comment_119684628

The cameras use what is known as downsampling. Usually they take the output from 4 or more pixels to create a single pixel in the output photo. This can reduce noise, particularly in low light situations.

"The central idea behind Nokia's original 'PureView' system was to have a large sensor with a high megapixel count - not for producing high megapixel images (though that's possible too), but for gathering enough light information that 'computational photography' became a reality. In addition to a degree of genuinely lossless digital zoom, the highlight for many people was 'oversampling', pulling information from multiple pixels on the sensor to produce 'perfect' pixels in a lower resolution output image.

This 'perfection' is manifested, in theory, by the elimination of digital (random) noise, since random pixel readouts at the pixel level get neatly averaged out as part of the oversampling process. In addition, there's better colour and illumination accuracy, again because values from underlying physical pixels can be cleverly averaged." http://www.allaboutsymbian.com/features/item/18351_Lumia_1020_and_its_oversamplin.php

Flinty997

How many have a DSLR and how many carry them everywhere.

My DSLR is an older one with a 6mp sensor. We stopped using it once mobile cameras got half decent for casual photos.

The issue in this case is they are selling a 108mp without OIS which is a bit pointless in my opinion. A pixel 4a will take better photos.

cnocbui

I have a proper camera and a couple of phones. Suggesting that the lenses in phones are inherently inferior in resolution to those in a ILC is making a misrepresentation of the facts.

Flinty997

The best camera is the one you have with you.

Irish Stones

https://www.boards.ie/discussion/comment/119695650#Comment_119695650

I have two DSLR, one with 18 Mp, the other one with 24 Mp, the newest one replaced the other. I used to carry them everywhere, and I took hundreds of thousands photos with them, until the end of 2019.

Then the pandemic, the lockdown, and the mental depression it carired along with it, and I lost any interest in photography with professional cameras. All my equipment (several lenses, professional flash, filters, and so on) has been forgotten in a cabinet, I haven't touched it in the last 36 months. And it's a pity, because the second body was purchased only a few months before the pandemic, so it is nearly untouched,

Since then I only used my phone, and I expected all my phones to take some decent pictures. I know I couldn't have anything comparable with the images from my professional cameras, but I wouldn't expect they were so bad either.

Flinty997

That you bought a phone with a mediocre camera is not the fault of the phone. You need to do your homework.

It's not representative of phones with good cameras either.

The best phones are 1k+ euro. That's not to say it's all about price. You still have to research it. But you know what segment of the market you're buying into when you buy a phone.

Irish Stones

https://www.boards.ie/discussion/comment/119699495#Comment_119699495

I relied on a few reviews on the web and youtube. I also knew that I couldn't have the best phone around at that price.

I owned a phone several years ago, and it took very good photos. So, this time I also relied on the fact that after a few years, technology might have improved and that what was good some years ago, was much better now.

Flinty997

It has improved. The price point has moved upwards through.

To get decent camera on a new phone you need to be spending 300+

Irish Stones

https://www.boards.ie/discussion/comment/119701626#Comment_119701626

I paid a little more than €300 for that phone, but it was on offer, and I guess the real price was around €360-380, even if right now I can find it as low as €230.

I also remember that I asked the forum for an advice on the phone and this one came among the favorite ones ☺️

Flinty997

Maybe I should have upped my price. Crazy prices. I know I got ours (with OIS) around 330 in deals.

You need OIS on a mobile.

Last best deal (for camera's on mobile) was Vodafone on the pixels.

https://www.boards.ie/discussion/2058198885/google-pixel-4a-for-199-on-vodafone-no-need-to-switch-number/p23

cnocbui

This is taken with the 16 MP OIS camera in a 2015 Samsung S6, with a crop showing the actual 1:1 detail from the sensor. The lenses in phone cameras can have very decent resolution, I think. I bought it in 2106 for €200 in mint condition.