The formats that keep arriving from somewhere
Nobody chooses TIFF or BMP on purpose any more, yet they keep turning up: a scanner writes a 200 MB TIFF, a fax gateway emails one, an old Windows program exports a BMP, a government portal sends archived documents as multi-page TIFF. Both formats predate the web, both are usually enormous, and both are awkward in a browser. Understanding why they are still produced makes it obvious what to convert them to.
TIFF: a container that can hold almost anything
Tagged Image File Format dates from 1986 and is less a format than a filing system for image data. A TIFF holds one or many images, each with its own compression scheme, colour space, bit depth and a set of tags describing it. That flexibility is exactly why professional scanning, publishing, medical imaging and geospatial work still use it — and why two TIFFs can have nothing in common beyond the extension.
| Compression inside the TIFF | Typical source | Size for one A4 page at 300 dpi |
|---|---|---|
| None | Lab equipment, some scanner 'archive' modes | 25 MB in colour |
| LZW or ZIP, lossless | Photoshop, publishing workflows | 8–15 MB |
| CCITT Group 4, black and white | Fax machines, office copiers | 30–80 KB |
| JPEG inside TIFF | Some camera and scanner software | 1–3 MB |
Two features cause most of the surprises. TIFF supports multiple pages in one file, so a scanned contract may be a single TIFF containing forty images — and most viewers show only the first, which is how people conclude that pages are missing. And TIFF supports CMYK colour for print, which browsers cannot display; a CMYK TIFF converted naively comes out with inverted or washed-out colour.
BMP: no compression, by design
The Windows bitmap format stores pixels essentially raw. Its size is almost exactly width × height × bytes per pixel, so a 1920×1080 screenshot is about 6 MB regardless of content — a photograph and a plain white rectangle come out the same size. There is a run-length encoding mode in the specification, but it is rarely used and only applies to low colour depths.
That is not a flaw so much as a choice from 1990: no compression means no decoding step, which mattered when a computer had four megabytes of RAM. Today it means a BMP is typically twenty to fifty times the size of the equivalent PNG with no quality advantage whatsoever, because PNG is also lossless. Converting a BMP to PNG is one of the very few conversions that is pure gain — identical pixels, a fraction of the bytes. BMP to PNG does exactly that.
What to convert to
- TIFF to JPG for photographs and colour scans you need to send or upload. This is the big win: a 40 MB lossless TIFF typically becomes a 2–4 MB JPEG that looks the same on screen.
- TIFF to PNG for documents, line art, screenshots and anything with sharp text, or where the file will be edited further. Lossless, so no artefacts around letters, but expect a larger file than JPEG.
- BMP to PNG essentially always. There is no case where keeping the BMP is better, unless a specific piece of legacy software demands it.
- For a multi-page TIFF that represents a document, the right destination is usually a PDF: convert the pages to images, then use Image to PDF to reassemble them in order into one file that opens anywhere.
Why your browser will not open a TIFF
No major browser decodes TIFF. Safari on macOS does, because the system frameworks handle it, which is a common source of confusion in mixed teams — the file opens on a colleague's Mac and fails on everyone else's machine. The reason nobody added it is that TIFF's flexibility is a liability in a browser: supporting every compression scheme, bit depth and colour space in the specification is a large amount of code exposed directly to untrusted files.
Practically, a TIFF is a working format for capture and archiving, not a delivery format. Keep the TIFF if it is your master copy, and convert a JPEG or PNG for everything that leaves your machine.
What to watch for when converting
- Check the page count first. If the source was a document scan, confirm you got every page and not just the first.
- CMYK sources shift colour. Converting print artwork to RGB changes it, sometimes noticeably in saturated colours. For anything going to a printer, let the print shop do the conversion.
- 16-bit TIFFs lose depth. Scientific and high-end photographic TIFFs may store 16 bits per channel; JPEG and standard PNG output reduce this to 8. Fine for viewing, not for further processing.
- Keep the original when the TIFF is an archival master. Conversion is a one-way door and the TIFF exists precisely because someone wanted a lossless record.
- Alpha channels in TIFF survive into PNG and are discarded by JPEG.