What is JPEG?
JPEG (Joint Photographic Experts Group) is a commonly used lossy compression method for digital images, particularly photographs. The format achieves significant file size reduction by discarding some image data that is less perceptible to the human eye.
Quick Facts
| Full Name | Joint Photographic Experts Group |
|---|---|
| Created | 1992 by Joint Photographic Experts Group |
| Specification | Official Specification |
How It Works
JPEG was created by the Joint Photographic Experts Group committee in 1992. It uses discrete cosine transform (DCT) to convert image data into frequency components, then quantizes and encodes them. The compression level is adjustable, allowing users to balance between file size and image quality. JPEG excels at compressing photographs and complex images with smooth color transitions but is not ideal for graphics with sharp edges, text, or transparency. The format does not support animation or transparency.
Key Characteristics
- Lossy compression - some quality loss with each save
- Adjustable compression ratio (quality 1-100)
- Excellent for photographs and natural images
- Does not support transparency or animation
- Uses DCT-based compression algorithm
- Smaller file sizes than PNG for photographs
Common Use Cases
- Digital photography storage
- Web images and thumbnails
- Social media image sharing
- Email attachments
- Print-ready photographs
Example
Loading code...Frequently Asked Questions
What is the difference between JPG and JPEG?
JPG and JPEG are the same format. The only difference is the file extension length. Early Windows systems limited extensions to 3 characters, hence .jpg. Other systems allowed .jpeg. Both extensions represent exactly the same JPEG-compressed image file with identical encoding.
Why doesn't JPEG support transparency?
JPEG was designed for photographs, which rarely need transparency. The DCT-based compression algorithm operates on 8x8 pixel blocks and doesn't include an alpha channel. For images requiring transparency, use PNG, WebP, or GIF formats instead.
What is the best JPEG quality setting for web images?
For most web images, 80-85% quality provides an excellent balance between file size and visual quality. This typically reduces file size by 70-80% compared to 100% quality with minimal visible difference. For thumbnails, 70-75% is often acceptable.
Why should I avoid saving a JPEG file multiple times?
JPEG uses lossy compression, meaning each save permanently discards data. Re-saving a JPEG file accumulates this loss, causing gradual quality degradation and more visible artifacts. Always keep original files and export to JPEG only as a final step.
When should I use PNG instead of JPEG?
Use PNG over JPEG for images with sharp edges, text, line art, logos, screenshots, or when transparency is needed. JPEG excels at photographs with smooth color gradients but creates visible artifacts around sharp contrasts and edges that PNG handles better.