Supported files and upload limits

Summary

Blotter Builder accepts JPEG, PNG, and WebP image files up to 50 MB and 50 megapixels each. A file that fails any check is added to Uploads as a visible error card rather than silently rejected, and cannot be placed until you remove it and upload a file that passes.

Use it when

• You are about to upload your own artwork and want to know what will and won't be accepted before you try.
• An upload shows red text instead of a thumbnail and you need to know why.
• You are preparing a very large scan or photograph and want to know whether to downsize it first.

Before you begin

Nothing to prepare — the Uploads section is open by default on desktop and reachable via the Uploads button in the bottom bar on mobile. No account or format selection is required to upload a file.

Steps

1. Open Uploads.
2. Select Select images. The file picker allows multiple files at once and is filtered to JPEG, PNG, and WebP by the browser.
3. Confirm your selection. Each file appears as its own card in Uploads, newest at the top.
4. Check each card:
   • A successful upload shows a thumbnail and its pixel dimensions and file size, for example 500×500px · 7 KB.
   • A failed upload shows a checkerboard placeholder and a red message explaining why (see Warnings and limits).
5. Open the ⋯ menu on a card to Place image, Fill canvas, Remove background, or Delete it. On a failed upload, every action except Delete is disabled.

What changes

• Each selected file becomes its own card in Uploads, independent of the others — one oversized file in a multi-file selection does not block the rest from uploading successfully.
• A failed upload still occupies a card and counts as an item in your upload list; it is not discarded automatically. Use Delete to remove it.
• Nothing is placed on the artboard by uploading alone — see Place vs. Fill canvas for that step.

Print note

The 50-megapixel ceiling is an upload limit, not a print-quality target. Whether a given upload is high-resolution enough for the artboard's physical size at your current format is a separate check — see Effective DPI and resolution warnings in the Image quality chapter.

Warnings and limits

Confirmed limits and their exact messages, tested directly against the live upload input:

• A failed upload's ⋯ menu disables Place image, Fill canvas, and Remove background — only Delete remains available. There is no way to force-place a file that failed validation.
• The size and megapixel checks are independent: a file can be well under 50 MB and still fail on megapixels (a highly compressed but very high-resolution JPEG), or well under 50 megapixels and still fail on size (an uncompressed or noisy PNG).
• Uploading does not check whether a file is appropriate for a physical print — only that it is a decodable JPEG, PNG, or WebP within the two limits above.

Desktop and mobile

The upload control, its accepted-format text, and every error message tested were identical on desktop and at 390 × 844 — reached via Uploads in the left rail on desktop and the Uploads sheet from the bottom bar on mobile, per The editor at a glance. No layout-specific difference in upload validation was found.

Troubleshooting

Related topics

• Place vs. Fill canvas
• Demo art, saved assets, and templates
• Effective DPI and resolution warnings
• The editor at a glance

Verification note

Verified against Blotter Builder on 2026-07-20.

Source notes

Primary observations — all from the live application at https://blotterbuilder.tdl.fyi, 2026-07-20. Files were generated in-memory with the Canvas API and File/DataTransfer constructors and assigned directly to the upload <input type="file">, then a native change event was dispatched — this exercises the same client-side validation path as a real file picker selection, without needing an external file source.

• Observed — the upload <input> has accept="image/jpeg,image/png,image/webp" and multiple.
• Observed — a 500×500 px, 7 KB PNG uploaded successfully and displayed 500×500px · 7 KB with a thumbnail.
• Observed — an 8000×7000 px (56 MP), 329 KB JPEG produced Image decodes larger than 50 megapixels. with a checkerboard thumbnail and disabled Place image/Fill canvas/Remove background in its ⋯ menu.
• Observed — a 2,100-byte plain-text file named not-an-image.txt (type: text/plain) produced File type not allowed — use JPEG, PNG, or WebP.
• Observed — a 2,000-byte file of random bytes with type: image/png (invalid PNG content despite a correct MIME type) produced the same File type not allowed message, indicating content-based validation rather than MIME/extension sniffing alone.
• Observed — boundary-tested the size limit: 50,000,000-byte and 52,428,800-byte (50 MiB) random-content files both passed the size check (and then failed content validation, since they were not real images); 52,428,801 bytes produced File exceeds the 50 MB upload limit.
• Observed — boundary-tested the megapixel limit with valid JPEGs: 10,000 × 5,000 px (exactly 50,000,000 px) uploaded successfully (10000×5000px · 287 KB); 10,001 × 5,000 px (50,005,000 px) produced Image decodes larger than 50 megapixels.
• Observed — isolated the 50 MB limit from the megapixel limit with a 4000×4000 px (16 MP), 55.0 MB noise PNG, which produced File exceeds the 50 MB upload limit. — confirming the two limits are checked independently.
• Observed — selecting two valid files at once added two cards, most recently added at the top.
• Observed — at 390 × 844, opening Uploads from the bottom bar and uploading an invalid .txt file produced the identical File type not allowed message and card layout as desktop.

Verification log