PJPEG File Format (.pjpeg)

PJPEG is progressive JPEG, a JPEG encoding choice rather than a different file format, where the image is built up through several increasingly detailed scans across the whole picture instead of filling in top to bottom in one pass.

.pjpegImage Files

PJPEG at a glance#

Full name	Joint Photographic Experts Group JFIF format
File extension	.pjpeg
Category	Image Files
MIME types	image/jpegimage/pjpeg
Other extensions	.jpg.jpeg.jpe
Compression	Lossy
FileFlip support	FileFlip reads and writes this format

What a .pjpeg file can hold#

These are the things a PJPEG file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Transparency (alpha channel)	No
Lossless compression	No
Embedded metadata	Yes
Colour profiles	Yes

Strengths and limitations of PJPEG#

What PJPEG does well

Shows a rough, full-size preview after only a fraction of the file has downloaded, sharpening in later passes instead of revealing top to bottom
Often compresses slightly smaller than baseline JPEG at the same quality, since each scan gets its own optimized Huffman table

Where PJPEG falls short

Takes marginally more memory and time to decode than baseline JPEG, since the decoder holds the whole image while later scans refine it
A handful of very old or embedded JPEG decoders can't read progressive scans at all

Choose progressive encoding for images shown over a slow or uncertain connection, where a quick blurry preview beats a slow top-down reveal.

Convert to baseline JPEG when a downstream tool or embedded device only supports the simpler sequential scan order.

How to open a .pjpeg file#

A .pjpeg file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts PJPEG into a format your machine already opens, and it does it in the browser tab rather than on a server.

Platform	Programs that open it
Windows	Photos, Paint, IrfanView, Adobe Photoshop
macOS	Preview, GIMP, Adobe Photoshop
Linux	GIMP, ImageMagick, gThumb
iOS	Photos
Android	Google Photos
Web	FileFlip, any web browser

PJPEG questions people ask#

What is PJPEG?

PJPEG is progressive JPEG, a JPEG file encoded in a handful of increasingly detailed scans instead of one pass from top to bottom. It's still a JPEG file, just encoded differently, and opens anywhere JPEG does.

What's the difference between PJPEG and a regular JPEG?

A regular, baseline JPEG fills the image in from top to bottom as it loads. PJPEG encodes several scans of the whole picture, each adding sharper detail, so a rough version of the entire image appears almost immediately and refines as more data arrives.

Does progressive JPEG reduce image quality?

No, PJPEG uses the same lossy JPEG compression as baseline JPEG at a given quality setting, and often produces a slightly smaller file because each scan can use its own optimized Huffman table.

Converting PJPEG files#

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.