JPG
How JPG compression works, when to use it vs PNG and WebP, and common mistakes with lossy screenshot formats.
JPG, or JPEG, is a lossy raster image format named after the Joint Photographic Experts Group. The core standard is ITU-T T.81, also published as ISO/IEC 10918-1 in 1992. Files use the .jpg or .jpeg extension and the MIME type image/jpeg.
JPEG stores 8 bits per channel and has no alpha channel. It supports baseline images, which load top to bottom, and progressive images, which load as a blurry full image that sharpens.
Nearly every device, browser, editor and upload form opens JPEG, which makes it the default format for photos and for sharing.
Convert image formats
Image Converter converts between JPG, PNG and WebP in the browser. PDF to JPG turns PDF pages into JPG images.
How JPG compression works
- Convert RGB to a brightness channel and two color channels (YCbCr).
- Often store the color channels at lower resolution, called chroma subsampling, such as 4:2:0.
- Split each channel into 8×8 blocks and apply a discrete cosine transform.
- Quantize the results, dropping fine detail. The quality setting controls this step.
- Compress the remaining values with Huffman coding.
JPG vs PNG vs WebP
| JPG | PNG | WebP | |
|---|---|---|---|
| Compression | Lossy | Lossless | Lossy or lossless |
| Alpha | No | Yes | Yes |
| Best for | Photos | UI, text, masters | Web images |
| Support | Universal | Universal | Current browsers and many apps |
When to use JPG
Use JPG for photo-heavy screenshots, long capture sessions where size adds up, and files sent by email. In Temposhot, JPG Export (Adjustable Quality) takes a quality from 1 to 100 with a default of 85, and Auto Export (Save as you go) also defaults to JPG quality 85. Website Capture saves JPEG by default.
Common mistakes
- Using low quality on screenshots with small text, which adds ringing around letters.
- Saving colored text on colored backgrounds, where chroma subsampling blurs edges.
- Re-saving the same JPG many times.
- Expecting transparency to survive.
Have an image to fix right now?
Reduce a JPG's size with Image Compressor.
Common questions
Are JPG and JPEG different?
No. Both names refer to the same format. Older systems limited extensions to three letters.
Is JPG at quality 100 lossless?
No. Quality 100 reduces loss, but the format is still lossy.
Sources
Related resources
- Export formats: PNG and JPG export options.
- General and history settings: Auto Export format and quality.
Taking the same screenshots again and again?
Temposhot captures a screen, window or area on a timer and exports the set as a PDF, images, ZIP or MP4. The free browser tools fix single images.
Related resources
Related terms
- PNGHow the PNG image format works, when to use it for screenshots, and how it compares to JPG and WebP.
- WebPWhat WebP is, how it compares to PNG and JPG, and when to use it for screenshots.
- Lossy CompressionWhat lossy compression is, which image formats use it, and how to balance file size against visual quality.
- Image QualityWhat determines image quality, how quality interacts with file size, and how to choose the right quality settings for screenshots and exports.
- Image CompressionWhat image compression is, lossy vs lossless explained, and common mistakes when compressing screenshots.
- Image FormatOverview of common image formats — PNG, JPG, WebP, AVIF — and when to use each.