How the rotation works
Choose an image and it is drawn onto a canvas in the browser. Pressing rotate right advances the angle by 90 degrees, pressing rotate left steps it back by the same amount, and four presses in either direction return you to where you started. There is no separate apply step: the preview you are looking at is the exported result.
On a quarter turn the canvas dimensions swap, so a 4000 by 3000 photo becomes 3000 by 4000. That matters because a naive rotation that keeps the original canvas size crops the corners off. Here the full frame is preserved and nothing is lost from the edges.
Everything happens on your device. The file is read into the tab, drawn, and the download is produced from memory. Nothing is uploaded, which is the right default for the personal photos and document scans that make up most of the rotating people actually need to do.
- Each press steps a quarter turn; four presses come back around
- Canvas dimensions swap on a quarter turn, so no corners are cropped
- The image is processed in the browser tab and never uploaded
Quarter turns only, and why that covers most cases
The rotation is in fixed 90 degree steps. There is no slider for an arbitrary angle and no straighten control for a horizon that is a couple of degrees off. That is a real limitation and worth knowing before you arrive with a tilted photo.
It also covers the overwhelming majority of real rotation problems. A photo taken with the phone turned, a scan fed into the scanner the wrong way round, a screenshot from a rotated display, a document photographed in landscape when it should be portrait: all of those are off by exactly a quarter turn or a half turn, because that is how cameras and scanners fail.
A quarter turn is also the only rotation that is geometrically clean. Rotating by 90 degrees moves every pixel to another exact pixel position, so nothing is resampled and no softness is introduced. An arbitrary angle has to interpolate, which always costs a little sharpness and leaves empty triangles at the corners that have to be cropped or filled.
What the exported file looks like
The export is always a PNG, regardless of what you put in. PNG is lossless, so the rotation itself costs nothing in quality, and it is the sensible default for screenshots, line art, logos, and scans of documents.
For photographs it has a cost worth naming. A JPEG photo re-exported as PNG typically becomes several times larger, because PNG does not use the frequency-based compression that makes JPEG small for photographic content. If file size matters, run the PNG through an image compressor or convert it back to JPEG afterwards.
Metadata does not survive. Canvas export writes pixels and nothing else, so EXIF fields including camera model, capture date, GPS coordinates, and the orientation flag are all absent from the result. That is a privacy benefit if you were about to share the photo and a loss if you were relying on the capture date, so keep the original if the metadata matters to you.
- Output is always PNG, which is lossless but large for photos
- EXIF metadata including date and GPS is not carried into the export
- Rotating by a quarter turn resamples nothing, so sharpness is untouched