What Is a JPG File? How JPEG Compression Works
A JPG is a lossy image format built in 1992 to make photographs small. Here is what JPG is, how its compression discards detail you cannot see, and when to use it.
A JPG file is an image saved in the format created by the Joint Photographic Experts Group in 1992, built for one job: making photographs small. JPG uses lossy compression, discarding visual detail the human eye barely notices to shrink files by 60 to 90 percent. That makes it the format of the web, email, and digital cameras. The cost is that some quality is permanently lost, and JPG cannot store transparency. This guide explains what JPG is, how its compression works, and the images it suits.
How JPEG compression works
JPG achieves its size by throwing away data your eyes are unlikely to miss. It divides the image into 8 by 8 pixel blocks, converts each block into frequency information, and discards the fine high-frequency detail humans perceive least. A quality setting from 0 to 100 controls how aggressive the discarding is. At high settings the loss is invisible; at low settings, blocky artifacts appear. This is lossy compression: the removed detail never comes back.
The quality setting
The quality dial is JPG's key control. At 90 the difference from the original is invisible at normal viewing distance, ideal for photos and screenshots with text. At 80, photographs still look great with a smaller file. Below 70, compression artifacts start to show around edges and text. Choosing the right quality balances file size against sharpness for the image at hand.
Pros and cons
- Pro: tiny files for photographs, 60 to 90 percent smaller than PNG.
- Pro: universal support on every device and platform.
- Pro: adjustable quality to balance size and sharpness.
- Con: lossy, so quality degrades slightly with every re-save.
- Con: no transparency, since it has no alpha channel.
- Con: smudges sharp text and thin lines at low quality.
When to use JPG
Use JPG for photographs, web images, email attachments, and upload forms that demand small files. Avoid it for logos, screenshots with text, and anything needing transparency, where PNG is the better choice. To turn a heavy PNG into a JPG, our converter does it in one step, with a quality slider and exact size targeting. See the PNG vs JPG guide for the full comparison.
Frequently asked questions
What is a JPG file?
A JPG is a lossy image in the JPEG format, built in 1992 to shrink photographs by discarding detail the eye barely notices.
What does JPG stand for?
It comes from the Joint Photographic Experts Group, the committee that created the format. JPG and JPEG are the same thing.
Is JPG lossy or lossless?
Lossy. JPG permanently discards detail to shrink the file, unlike PNG, which is lossless and keeps every pixel.
Does JPG support transparency?
No. JPG has no alpha channel, so transparent areas are filled with a solid colour when you convert to it.
When should I use JPG?
Use JPG for photographs, web images, and upload forms. Avoid it for logos, text-heavy screenshots, and transparency, where PNG is better.