Object Storage Service (OSS) returns this error when you convert an image to WebP format and the source image exceeds 16,383 pixels in width or height.
Cause
The WebP format uses 14-bit fields to encode image dimensions, which caps the maximum width and height at 16,383 pixels. This is a WebP format-level constraint, not an OSS-specific limitation -- any tool that processes WebP images is subject to the same limit.
Solution
Reduce the image dimensions below 16,383 pixels in both width and height before converting to WebP.
Option 1: Resize with OSS image processing parameters
Append resize parameters to the image processing URL to scale the image down before format conversion. For example, if the source image is 20,000 x 15,000 pixels, limit the longest side to 16,382 pixels:
https://<your-bucket>.<region>.aliyuncs.com/<object-key>?x-oss-process=image/resize,l_16382/format,webpReplace the following placeholders with your actual values:
| Placeholder | Description | Example |
|---|---|---|
<your-bucket> | OSS bucket name | my-image-bucket |
<region> | Region endpoint | oss-ap-southeast-1 |
<object-key> | Object key of the source image | photos/large-banner.png |
The resize,l_16382 parameter scales the image proportionally so that the longest side does not exceed 16,382 pixels. OSS applies the resize before the format conversion, which prevents the error.
Option 2: Convert to a different format
If you need to preserve the original dimensions, convert to a format that supports larger dimensions, such as JPEG or PNG. These formats do not have the 16,383-pixel limit.
https://<your-bucket>.<region>.aliyuncs.com/<object-key>?x-oss-process=image/format,jpgJPEG does not support transparency. If the source image has a transparent background, use PNG instead.