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I've long noticed that phone cameras have an oil painting like effect on human skin.

As phone cameras get better, the effect is less pronounced by it's still a significant difference from a bigger camera.

Why is that? I would assume this is sensor size related, but what at the technical level here is happening?

Below is a sample of photos of human skin taken from a few different cameras

https://3.img-dpreview.com/files/p/E~forums/66603467/aae6ea2a0a6e4977b3b0fa6df51585f8

From left to right

iphone 12, iphone 14 pro jpeg, iphone 14 pro RAW 48, iphone 14 pro RAW 48 exported as jpeg from macOS Photo, A1+SEL24GM

Here is a photo of close up of all the human skin (arm area)

https://4.img-dpreview.com/files/p/E~forums/66603467/9a0e19eea8084bb4974d817c4d20f00e

We can see that on the far left, the effect is worst. It feels like someone just brushed the photo with a paint brush of a single skin color.

On the far right the photo taken with a FF camera. It's a complete 3d arm finally. The highlight roll offs is smooth in the middle of the arm. The shadow at the edge is well defined.

One can maybe blame the lack of dyanmic range for this effect. But why? We're not talking about details in the sky or any extreme highlights area. It is as if the phone cameras is running out of shades to represent human skin.

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You just noticed that camera phones don't actually show you the image. Camera phones create a computational model for what you see, and then use that computational model to create the individual pixels.

I think there are two major reasons why this is the case: low light and zoom.

Most cameras don't have continuous optical zoom, but most users demand continuous zoom. In some cases, a secondary camera with different focal length could help a bit, but that suffers from three problems: (1) it only gives two distinct focal lengths and not the continuous zoom that users demand, (2) it has parallax error, (3) the zoomed-in camera can't be achieved with a longer real focal length since real focal lengths are as much as phone thickness allows, so it's achieved usually by a smaller sensor (even larger crop factor, creating lots of noise even in decent light). So to allow a reasonable continuous zoom, what cameras need to do is to create a computational model for what you see in the picture, then use that computational model to recreate the image at the zoomed-in resolution. I suspect the manufacturers "for simplicity" use the same image processing pathway even if you take an image at 1:1 pixel mapping. Otherwise users might complain that the image style jumps from "real" to "painting-like" if you even zoom in a tiny tiny bit.

Secondly, the low light performance of small camera phone sensors is horrible. In photography, "low light" means basically everything except outdoors during daylight. Yes, with a camera phone sensor you can't take a reasonable image indoors even if your ceiling has lots of very bright lights. Even the flash doesn't help, since camera phones don't have a real Xenon flash but rather a feeble LED light that only helps in about complete darkness, or if taking a photograph of a receipt 30 cm away.

This means that camera phones as-is are about useless in most situations where they might be used. To solve these issues, camera phones have to have so high amounts of denoising that no DLSR or mirrorless camera would need that insane denoising amounts. So they do the denoising with lots of artificial intelligence on a fast processor that has special artificial intelligence capabilities. I suspect that denoising is used "for simplicity" even if it isn't strictly speaking needed, like in bright sunlight.

Those computational photography algorithms seem to often create a painting-like image, not what you would see with your eyes or in an image taken by a professional camera.

Finding if there's some way to shoot RAW images without the computational photography could help, but only in direct sunlight as the noise in those RAW images would make them useless in about every different situation.

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  • \$\begingroup\$ I mean I don't disagree with anything you said but it's sorta off topic. I'm only concerned with outdoor non-zoomed photo of human subject (as provided by my samples). \$\endgroup\$
    – erotsppa
    Commented Nov 13, 2022 at 23:48
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This is because the mobile camera software uses the default soft skin effect feature, and in the final image, the person's skin is retouched and without hair and pores, it is unlikely that the original and initial image recorded by the sensor It is oiled and soft with this feature, and these adjustments are applied to the photo after processing the initial image. Usually, some famous mobile companies use this effect without the user's permission for a more popular output.

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It could be a smoothing effect which camera application performs it. Take a photo from another simple-textured areas and see smoothness there. You can weaken it using sharpener effect.

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