Why does rotating a very large photo by a free angle fail on my phone?
Because 'Expand to fit' at a free angle builds a canvas bigger than your original photo, sometimes much bigger, and the browser on a phone has limited memory to draw it. The tool warns you when the output goes over 50 megapixels and shows an error message if drawing fails. The fix is to shrink the photo first, choose 'Original size, clip', or do the rotation on a computer.
How much does the canvas grow?
At anything other than a right angle, the tilted rectangle needs a wider and taller canvas to fit whole, and the worst case is around 45 degrees. These are the tool's figures for a 7000 × 7000 square photo, 49 megapixels, close to the largest the tool accepts:
At 10 degrees with expand: an 8110 × 8110 canvas, about 66 megapixels.
At 33 degrees: a 9684 × 9684 canvas, about 94 megapixels, nearly double the original.
At 45 degrees: a 9900 × 9900 canvas, about 98 megapixels.
With 'Original size, clip' at any angle: it stays 7000 × 7000, 49 megapixels.
The browser draws the whole canvas in memory before saving, and every pixel takes several bytes, so a canvas this size needs hundreds of megabytes of memory. We tested a 49 megapixel photo at 33 degrees and it worked in desktop Chromium, but phones put lower limits on large canvases, and drawing can fail or the page can close.
Reassuring news: ordinary phone photos are fine
A common 4032 × 3024 phone photo, about 12 megapixels, turned 33 degrees becomes 5029 × 4733, only about 24 megapixels, and no warning appears. The problem is with huge images from professional cameras and high resolution scans.
The fixes, in order
- Shrink the photo first with the Image resizer to the size you actually need. An online store photo rarely needs 7000 px.
- If the size matters to you, choose 'Original size, clip' in the Image rotator and flipper tool, so the canvas does not grow, and accept that the edges are cut.
- At 90 or 180 degrees there is no problem at all: right-angle turns do not enlarge the canvas, they only swap width and height.
- If you need the huge photo whole at a free angle, do it on a computer.
Signs you are close to the limit
- A warning saying the output is about so many megapixels and may fail on devices with little memory.
- The 'Output:' line under the preview shows the final dimensions before you download, so watch it as you change the angle.
- The tool refuses images over 50 megapixels or 40 MB from the start.
Common questions
Does the preview itself use a lot of memory?
No, the preview draws a reduced copy. The heavy memory use comes at download, which draws the full-resolution image.
Why did the warning appear but the download work?
The warning is a precaution. Some devices cope with large canvases and some do not.
Does the tool upload the photo to a more powerful server?
No, everything happens in your browser, which is why your device's memory is the limit.