What Is a JPG (JPEG) File? The Photo Format Explained

How JPG compression works

JPG uses lossy compression, meaning it permanently throws away image data to shrink the file. It does this cleverly: it breaks the image into small blocks, converts each into frequency information, and discards the fine, high-frequency detail the human eye is least able to notice. A photograph with smooth skies and gradual shading survives this beautifully — a JPG can be one-tenth the size of the raw pixels with no visible difference at normal viewing size.

The catch is that "least noticeable" is not "not there". Every time a JPG is re-saved, another round of detail is discarded, so editing and re-exporting the same JPG repeatedly slowly softens it — a phenomenon sometimes called generation loss. Around hard edges and text, JPG also produces visible "artifacts": faint halos and blocky smudges where its block-based math struggles with sharp transitions. That is why JPG is wrong for screenshots and logos even though it is right for photos.

When JPG is the right choice

Reach for JPG whenever the image is a photograph or photo-like and file size matters: camera photos, website hero images, email attachments, social posts, product shots. At a sensible quality setting (roughly 75–85 on a 0–100 scale), the file is small and the loss is invisible. It is the safe, universal default that every device, browser, printer and website accepts without a second thought.

Avoid JPG for anything with crisp edges, flat colour or text — screenshots, diagrams, logos, line art — where its artifacts show, and for images that need a transparent background, which JPG cannot store at all (it fills every pixel, usually with white). Those belong in PNG. Avoid it too as a working master for images you will keep editing; keep an original in a lossless format and export JPGs as the final deliverable.

JPG vs newer formats

JPG is not the most efficient format any more. WebP files are typically 25–35% smaller at the same quality, and AVIF smaller still, both while also supporting transparency and animation. On the modern web those formats are worth using. But JPG keeps winning on one thing that matters enormously: it opens literally everywhere, on every device and every piece of software ever made, with zero risk of a "cannot display this file" error.

That universality is why JPG remains the right format for a photo you are handing to someone else — an email, a print order, an upload form that might be old. Use WebP or AVIF for images you publish on a site you control; keep JPG for images that need to travel to unknown destinations.

How to open, convert and shrink a JPG

Every device opens JPG by default — you never need special software to view one. To make it smaller for email or upload, run it through an image compressor (which re-encodes at a lower quality) and, just as importantly, resize it to the dimensions it will actually be displayed at; a 4,000-pixel photo shown at 800 pixels is wasting most of its size. To convert a JPG to PNG (for transparency or lossless editing) or from HEIC, WebP or PNG into JPG, use an image converter. OfficePad does all of this in your browser, so the photo is never uploaded.

Frequently asked questions