8 formats documented
A reference for the formats document work runs through.
Choosing a format badly is the most common cause of a file that is ten times larger than it needs to be, or a photograph that looks like it was faxed. Each page here explains what a format actually is, then says where it stops being the right answer.
These are explanatory pages rather than tool pages. Where a conversion genuinely works in a browser it is linked; where it does not, the page says so instead of sending you to something that will disappoint you.
Side by side
Every format at a glance
Compression character is read from each format’s own specification table, so it cannot contradict the detail page. A dash means the question does not apply — PDF is a container, and what matters is how the images inside it were compressed.
Contracts
- Compression
- —
- MIME
- application/pdf
JPG
.jpgPhotographs from cameras and phones
- Compression
- Lossy
- MIME
- image/jpeg
PNG
.pngScreenshots
- Compression
- Lossless
- MIME
- image/png
WebP
.webpPhotographic imagery on websites where page weight and load time are measured and budgeted
- Compression
- Both
- MIME
- image/webp
DOCX
.docxDocuments still being written or revised
- Compression
- —
- MIME
- application/vnd.openxmlformats-officedocument.wordprocessingml.document
XLSX
.xlsxFinancial models and budgets where assumptions feed calculated outputs
- Compression
- —
- MIME
- application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
PPTX
.pptxTalks and lectures delivered live
- Compression
- —
- MIME
- application/vnd.openxmlformats-officedocument.presentationml.presentation
TIFF
.tifDocument and archival scanning
- Compression
- Uncompressed, LZW, ZIP/Deflate, PackBits, CCITT Group 3/4, JPEG-in-TIFF
- MIME
- image/tiff
In detail
Read the full reference
- Portable Document Format.pdf
PDF
A fixed-layout page description format: the page you author is the page everyone sees. Open-standard since 2008, and the reason it is everywhere.
- Joint Photographic Experts Group image.jpg
JPG
The format photographs live in. Lossy block-based compression trades detail you are unlikely to notice for files small enough to send.
- Portable Network Graphics.png
PNG
Lossless, with a genuine alpha channel. The correct home for screenshots, logos, UI and anything with hard edges you cannot afford to soften.
- Web Picture format.webp
WebP
A single modern format covering the jobs JPEG, PNG and animated GIF used to split between them — usually at a noticeably smaller size.
- Office Open XML word processing document.docx
DOCX
A ZIP container of XML describing a reflowable document. Pagination is not stored — it is calculated when the file is opened.
- Office Open XML spreadsheet.xlsx
XLSX
A spreadsheet is a grid of cells where formulas reference other cells. XLSX stores that dependency graph, not a printed page.
- Office Open XML presentation.pptx
PPTX
A presentation is a sequence of slides built on inherited layouts, carrying media, animation and timing. Little of that survives flattening.
- Tagged Image File Format.tif
TIFF
Not one encoding but a container that can hold many. The long-standing standard in scanning, fax and prepress, and unreadable in a browser.
The short answer
Match the format to the content, not to habit.
Nearly every format complaint traces back to one mismatch: a photograph stored in a lossless format that cannot compress it, or a screenshot of text stored in a lossy one that smears every letter edge. The formats are not competing — they were designed for different pictures.
- Continuous tone
- Photographs and scans of photographs want lossy compression. Their detail is noisy enough that discarding some of it is invisible.
- Hard edges
- Text, diagrams, screenshots and line art want lossless compression. Their detail is exactly the thing lossy encoders throw away first.
For a document that must look identical to everyone who opens it, the answer is PDF — and then the question becomes how the images inside it were encoded, which is where the pages above become useful.