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1500×500 JPEG · 3:1
Each social platform crops uploaded media to its own aspect ratio before showing it in feeds. Uploading at the platform's native size — here, the platform feed posts — preserves the framing you intended and avoids the soft-focus that comes from the platform's own resampler. This preset outputs 1500×500 JPEG at the 3:1 ratio that the platform expects.
| Output dimensions | 1500×500 pixels |
|---|---|
| Aspect ratio | 3:1 (3:1) |
| Output format | JPEG @ 90% quality |
| Processing | 100% in your browser — no upload |
| Cost | Free, unlimited |
| Source | Official guidelines |
This preset is a deterministic recipe — every step has fixed parameters so the result is byte-identical across runs of the same input.
Mastodon Profile Header crops your input to 3:1 and resizes it to 1500×500 px as JPEG — a 750-kilopixel output. The work runs through canvas APIs and a WebAssembly image-encoder; the source image is decoded into an off-screen canvas, transformed in place, and re-encoded without any network upload.
Social-platform uploads frequently re-encode the file at the platform's CDN; running this preset locally before upload lets you see the exact pre-upload state. The browser-side path also means the file never leaves your device — relevant when the input contains personally identifiable information, screenshots of private documents, ID scans, or proprietary product photography.
1500×500 px, saved as JPEG at quality 90%.
The target platform — see the cited spec — uses 3:1 as its native frame. Submitting any other ratio means the platform's own crop runs, which often clips faces or text near the edge.
The target accepts JPEG, and JPEG compresses photographic content 5-10× smaller than PNG with no visible difference at quality 90%. PNG is the right choice only when the image has hard edges or transparency — which photo-ID, social posts, and product photos don't.
No. This preset runs entirely in your browser using WebAssembly + canvas APIs — no server round-trip. You can verify this in your browser's network panel: only static asset requests, no image upload. The file never leaves your device.