Rotate & Flip Image

Most photographs taken on a phone or camera are stored in the sensor's native orientation regardless of how the device was held. Rather than rewriting the pixels, the camera records an EXIF orientation tag saying how the image should be turned when displayed. Software that reads the tag shows the photo the right way up; software that ignores it shows the raw sensor data, sideways.

That is why a picture looks correct in your phone gallery, correct in one browser, and rotated ninety degrees after being uploaded to a form or opened in an older program. The image was never actually rotated — only labelled. Rotating properly rewrites the pixel data so the image is correct everywhere, with no tag to be ignored, which is what makes it the reliable fix before submitting a photo anywhere.

Turning an image by exactly 90, 180, or 270 degrees is a rearrangement of existing pixels. Nothing is interpolated, nothing is resampled, and no quality is lost no matter how many times you do it.

Rotating by an arbitrary angle — straightening a crooked horizon by two degrees, for instance — is a different operation entirely. The pixel grid no longer lines up, so every output pixel has to be calculated from several input pixels, which softens fine detail slightly. It also leaves empty triangular corners that must be cropped away or filled, so the image gets smaller. Neither is a reason to avoid straightening; it is a reason to do it once, from the original, rather than repeatedly.

They are easy to confuse and produce different results. Rotating turns the image around its centre and preserves the scene exactly. Flipping mirrors it, which reverses the content — text becomes unreadable, faces look subtly wrong, and anything with a left and right side is now backwards.

The distinction matters most in two places. Photographs of documents should never be flipped, because the text reverses. And selfies taken with a front-facing camera are usually already mirrored by the phone, which is why handwriting and logos in a selfie appear backwards; flipping horizontally corrects that, and rotating does not. If a scanned page comes out both sideways and mirrored, it needs one of each operation, applied in either order.