Convert images locally, with predictable trade-offs

Supported formats

The file picker explicitly accepts JPG/JPEG, PNG, WebP, and QOI. It can export those four formats plus raw RGBA pixel bytes. Other images may work when the browser itself can decode them, but they are not advertised as dependable inputs. In particular, HEIC is not guaranteed across current browsers.

What happens during conversion

1. The browser reads the selected file.
2. QOI is decoded by day2dayfile's own JavaScript decoder. Other supported images are decoded with createImageBitmap.
3. The pixels are drawn to an in-memory Canvas at the selected bounding dimensions.
4. Canvas exports JPG, PNG, or WebP; day2dayfile's encoder writes QOI; raw export writes the RGBA bytes.
5. The result becomes a temporary blob: URL for download. It is revoked when the result is removed or the tab closes.

Quality, size, and resolution

The default preset fits the image inside 1920 × 1080 without stretching it. The quality slider affects lossy Canvas exports such as JPG and lossy WebP; it cannot make PNG or QOI lossy. Turning compression off disables resizing and requests maximum export quality. If the input and output formats are already the same, turning compression off returns the original file unchanged instead of re-encoding it.

Transparency and metadata

JPG cannot store transparency, so transparent areas are filled with white. Re-encoding through Canvas normally removes EXIF, GPS, camera details, color-profile metadata, and other non-pixel data. That can be useful for privacy, but it also means this tool is not appropriate when metadata must be preserved. Original-file passthrough retains everything because it does not rewrite the file.

Important limitations

• Animated or multi-frame images may be reduced to one frame.
• Very large pixel dimensions can exhaust browser memory even when the compressed file is small.
• Raw RGBA contains only pixel bytes; it has no dimensions or descriptive header.
• Browser encoding implementations can produce slightly different sizes from the same quality setting.