What is JPG (JPEG)?
JPG (JPEG) is a lossy image compression format developed in 1992, widely used for photographs and web images due to its excellent balance of quality and small file size.
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What is JPG / JPEG?
JPG (also written as JPEG - Joint Photographic Experts Group) is a lossy image compression format created in 1992. It is the most widely used image format on the internet, in digital cameras, and on smartphones worldwide.
The format works by discarding image data that the human eye is least likely to notice, achieving dramatic file size reductions. A high-quality JPEG can be 10x smaller than an uncompressed version of the same image with virtually no visible quality loss.
How JPEG Compression Works
JPEG compression is built on the discrete cosine transform (DCT). The encoder splits the image into 8x8 pixel blocks, converts each block from the spatial domain into frequency coefficients, and then quantizes those coefficients, deliberately discarding the high-frequency detail that human vision is least sensitive to[1]. The remaining data is then packed with lossless entropy coding (Huffman or arithmetic), so the saved file is much smaller than the original pixels.
Because quantization throws information away, JPEG is a lossy format: every time a JPEG is re-saved it is recompressed and loses a little more detail, an effect known as generation loss[4]. The amount of loss is controlled by a quality setting, typically expressed from 1 to 100, that scales the quantization tables.
History and Standardization
The format is named after the Joint Photographic Experts Group, the committee that created it, and the core method was standardized internationally as ITU-T T.81 / ISO/IEC 10918-1 in 1992[1]. What most people call a "JPG file" on disk is usually wrapped in the JPEG File Interchange Format (JFIF) or an Exif container, which add the headers and metadata that applications and cameras rely on[3].
The .jpg and .jpeg extensions are identical; the three-letter form is a holdover from older systems that limited extensions to three characters. Browsers identify the format by the image/jpeg media type rather than the extension[2].
Technical Specifications
JPG vs Other Image Formats
| Feature | JPG | PNG | WebP | AVIF |
|---|---|---|---|---|
| Compression | Lossy (DCT)[1] | Lossless | Lossy & lossless | Lossy & lossless |
| Transparency | None[2] | Full alpha | Full alpha | Full alpha |
| Color depth | 8-bit/channel | Up to 16-bit | 8-bit | Up to 12-bit (HDR) |
| Compression efficiency | Baseline | Larger files | ~25-34% smaller than JPG | Smallest |
| Browser support | Universal[1] | Universal | All modern browsers | Most modern browsers |
| Best for | Photographs | Logos, screenshots | Modern web images | High-efficiency web/HDR |
JPG remains the universal default for photographs; newer formats like WebP and AVIF achieve smaller files at similar quality but with narrower (though now broad) support.
Pros & Cons of JPG
Advantages
Dramatic compression with minimal visible quality loss - up to 10x smaller than uncompressed.
Supported by every browser, device, camera, and operating system in existence.
Quality setting 1–100 gives full control over the size vs quality trade-off.
Perfect for photographs and complex images with millions of colors and gradients.
Disadvantages
Each save re-compresses the image causing gradual quality degradation over time.
Does not support alpha channel - transparent areas are filled with white.
Blocky artifacts appear at low quality settings especially around sharp edges.
Not suitable for text, logos, or flat-color graphics - use PNG or SVG instead.
When to Use JPG
JPG is the right choice for most photographic content and anywhere file size is a priority.
Photography
Digital cameras and smartphones save photos as JPG by default. Perfect for portraits, landscapes, and natural scenes.
Web Images
Smaller file sizes mean faster page loads. Use JPG for all photographic web content.
Social Media
Most social platforms re-compress uploads to JPG. Upload as JPG for predictable quality control.
Email & Sharing
Small JPG files are easy to share via email and messaging apps without hitting size limits.
Need to Convert or Compress JPG?
Use our free online tools to compress JPG files, convert JPG to PNG, WebP, PDF, and more - no signup required.
Try Image Converter FreeFrequently Asked Questions
What is the difference between JPG and JPEG?
There is no difference - they are the same format. JPG became common because early Windows limited extensions to 3 characters.
Does saving a JPG multiple times reduce quality?
Yes. Each save re-applies lossy compression causing gradual degradation. Keep originals in PNG and export to JPG only as a final step.
What quality setting should I use for JPG?
For web use quality 70–80 is ideal. For print use 85–95. Quality above 95 rarely makes a visible difference but significantly increases file size.
Can JPG files have a transparent background?
No. JPG does not support transparency. Use PNG, WebP, or SVG instead. JPG fills transparent areas with white by default.
Is JPG or PNG better for web images?
For photographs JPG is smaller. For graphics and text PNG is better. For modern web use, WebP outperforms both.