Why photos end up sideways
A camera sensor always records the picture the same way round. When you turn the phone to portrait, most cameras do not rotate the pixels; they save them in landscape order and add a small EXIF tag that says "display this rotated by 90 degrees". Apps that read the tag show the photo upright, apps that ignore it show it sideways. That is why an image can look fine in your gallery and wrong after uploading it to a website, attaching it to an older email client or placing it in a document.
Other common cases:
- Scans and document photos taken from above, where the phone could not tell which way was up.
- Screenshots or exports that need to be landscape for a slide or a print layout.
- Selfies that the front camera mirrored, so text in the background reads backwards.
How rotation and flipping work here
The tool decodes each image in a background worker inside your browser, draws it onto a canvas with the chosen transformation and encodes it again. Modern browsers apply the EXIF orientation tag while decoding, so the angle you pick is relative to how the photo appears in the browser, not to the raw sensor data.
- 90° turns the image a quarter turn clockwise. Width and height swap, so a 4000 by 3000 photo becomes 3000 by 4000.
- 180° turns it upside down; the dimensions stay the same.
- 270° is a quarter turn counter-clockwise.
- 0° leaves the angle alone, which is what you want when you only need a mirror image.
The flips mirror the picture: horizontal swaps left and right, vertical swaps top and bottom. A flip is not the same as a rotation. Rotating by 180° keeps text readable but upside down; flipping vertically makes it read backwards as well. Combining both flips gives exactly the same result as 180°.
When you set an angle and a flip together, the flip is applied to the picture as you see it first, and the result is then rotated. If a combination does not come out as expected, try the other flip direction; for a 90° or 270° turn, horizontal and vertical flips trade places visually.
Quality and file size
Rotating pixels is not lossy in itself, but saving the result can be:
- PNG is lossless, so rotated PNG files contain exactly the same pixels in a new order. Transparency is preserved.
- JPG and WebP are re-encoded at 92% quality. On photos this is visually indistinguishable from the original, but it is a new compression pass, so avoid rotating the same JPG back and forth many times. Pick the final orientation and do it in one step.
The output file size often differs from the input. Cameras usually save JPG at 95% quality or higher, so a rotated copy at 92% tends to be somewhat smaller. A heavily compressed JPG from a messenger may grow slightly instead, because the encoder does not try to match the original's settings.
Orientation metadata after rotating
Because the image is re-encoded from the canvas, the rotated file is written without EXIF metadata. The pixels are now in the correct order, so there is no orientation tag left to misinterpret and the photo looks the same in every viewer, upload form and document.
The same step also drops the rest of the metadata: camera model, capture date and GPS location if the phone recorded it. That is usually a privacy benefit when publishing photos, but if you need to keep the capture date for sorting a photo library, rotate a copy rather than the original. To inspect what a photo contains before or after, use the EXIF viewer.
Practical tips
- Set the angle and flips before dropping files. The settings apply to every file added afterwards, so you can process a whole folder of portrait scans in one go and download them as a ZIP.
- Sort mixed batches first. If some photos need 90° and others 270°, run them as two batches instead of fixing them one by one.
- For scanned pages, rotate first, then trim the margins with crop image, since cropping is easier when the page is already upright.
- Rotating a video is a different job, because every frame must be re-encoded; use rotate video for clips recorded in the wrong orientation.
The output keeps the original file name and format, so a rotated IMG_2041.jpg downloads as IMG_2041.jpg. If you download into the same folder, your browser will usually add a number to avoid overwriting the original.