If the phone is upside down, why does the picture come out right-side up, instead of upside down?
Edit: changed sideways to upside down; better example of my question
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that’s on your phone and/or camera app. mine – xiaomi, standard camera – does save photos as landscape
Because the camera and the screen are indexed to each other; the bottom of the camera captures the bottom of the image which is shown on the bottom of the screen. As you rotate the phone clockwise (for example), the bottom of the camera rotates to the left and upwards. That means the bottom of the image is now at that angle as well. However, the phone screen is also at that angle, so it cancels out the change.
With regard to landscape and portrait modes, the camera is programmed to understand that when the camera is held sideways, it should rotate the resulting image by 90 degrees so that it comes out “wide” rather than “tall.”
You can trick this if you take a picture at a weird angle; for instance, trying to take a picture straight downwards, if you tilt it one way or another, you’ll see the camera try to orient which side is down. I’ve taken a number of pictures which came out “upside down” because the phone was tilted too far “backwards” and the camera thought the far side of the phone was “down.”
This is because phones are smart these days. They contain a little device that can measure or “meter” acceleration, called an “accelerometer”. The most common acceleration we experience is gravity that constantly pulls us downward.
By looking at the output of the accelerometer the phone can know what its orientation is with regard to gravity and orient the photo properly. Without that point of reference, such as if you were floating in free fall, then it wouldn’t know to reorient the picture.
Modern phones have an accelerometer that measures the direction gravity is pulling, so the phone knows which way is down.
The Jpeg format your phone saves pictures in has metadata telling the viewer software which orientation the picture was taken in, and the viewer software will rotate the image to match.
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