Why photos arrive sideways
A phone camera almost always saves the image in the sensor's own orientation and records how it should be turned as an EXIF metadata tag. Software that reads the tag shows the photo the right way up; software that ignores it shows the raw sensor data, which is why the same picture can look correct in your gallery and lie on its side once uploaded.
This tool reads the tag, so the preview matches what your phone showed you. More usefully, the rotation is baked into the output pixels rather than left as metadata. The exported file looks correct everywhere, including in the systems that caused the problem in the first place.
Quarter turns are lossless, free angles are not
Rotating by 90 or 180 degrees just moves pixels to new coordinates. Nothing is interpolated, nothing is averaged, and the image is mathematically identical apart from the final encoding step. Export to PNG and a quarter turn is completely lossless.
A free angle is different. The pixel grid no longer lines up with the original, so every output pixel has to be calculated from a blend of its neighbours. The effect is small and usually invisible on photographs, but fine text and hard edges soften slightly. That is unavoidable in any software; the practical advice is to rotate once from the original rather than nudging the same file repeatedly.
Straightening a crooked horizon
Use the fine angle control rather than the quarter-turn buttons. Positive values turn clockwise, negative counter-clockwise, and the step is a tenth of a degree because that is the resolution the eye actually notices at photo sizes.
| Problem | Typical correction |
|---|---|
| Slightly tilted handheld shot | 0.5° to 1.5° |
| Visibly crooked horizon or building | 1.5° to 3° |
| Scanned document or photo | 0.5° to 2° |
| Deliberate diagonal composition | 5° to 15° |
A reliable method: find something in the frame that should be perfectly horizontal or vertical — a horizon, a door frame, the edge of a table — and adjust until it lines up with the edge of the preview box. Trying to judge the whole image at once is much harder than judging one line.
The corners problem
Turn a rectangle by anything other than a multiple of 90 degrees and it no longer fits its original frame. The canvas has to grow, and four triangular areas at the corners have no image data in them. Every tool has to decide what goes there, and you have three options:
- Fill with a colour. White works for documents and scans, black for photographs on dark pages. Pick anything that matches where the image will sit.
- Keep them transparent. Export to PNG or WebP and the corners stay empty, so whatever is behind the image shows through. JPEG cannot do this — it has no transparency channel.
- Crop them away. The cleanest result for a straightened photo: rotate here, then crop the largest rectangle that contains no empty corner. You lose a few percent around the edges, which is why photographers leave a little margin when they know a shot is crooked.
Rotating versus flipping
Rotation turns the image around its centre and leaves it readable. Flipping mirrors it, swapping left and right or top and bottom — any text in the image comes out backwards. They are different operations for different jobs.
Flip horizontal is the one people usually want. It corrects front cameras that save the mirrored preview you saw while composing, and it is how you turn a subject to face the other way in a layout. Flip vertical is rarer outside of reflection effects. Both can be combined with a rotation; applying both flips together is the same as turning the image 180 degrees.
Working in batches
Every image you drop in receives the same angle and flip settings, which is exactly what you want for a folder of scans that all came out sideways, or a set of photos from a camera that was mounted upside down. The preview shows the first image so you can confirm the settings before committing to the whole set, and results are returned as a single ZIP.
Because the work happens in your browser rather than on a server, none of your images are uploaded, there is no file count limit and no queue — the only constraint is your device's memory.