JPEG (Joint Photographic Experts Group)

GISBox is a one-stop 3D GIS data editing, conversion and publishing platform that supports editing in multiple GIS formats such as OSGB/GEOTIFF/RVT, converting to 3DTiles/Terrain and publishing.

Introduction

JPEG (Joint Photographic Experts Group) is a file format widely used for digital image compression, with the extension “.jpg” or “.jpeg”. It was developed by the Joint Photographic Experts Group established in 1986 and was officially adopted as an international standard (ISO/IEC 10918-1) in 1992. JPEG mainly uses lossy compression, which can significantly reduce the size of image files with a high compression rate. Therefore, it is widely used in digital cameras, websites, social media and other fields.

File Structure

JPEG files consist of the following data structures:

**SOI (Start of Image): **image file start marker.
**APP0~APP15: **application-specific data segment (such as EXIF information).
**DQT (Define Quantization Table): **quantization table definition.
**DHT (Define Huffman Table): **Huffman coding table.
**SOS (Start of Scan): **the starting part of the image data.
**EOF (End of Image): **image file end marker.

Pros

**High compression rate: **Using lossy compression algorithm can significantly reduce file size, thus saving storage space.
**Wide compatibility: **JPEG is supported by almost all devices and software, and has strong compatibility.
**Rich color expression: **Supports up to 16.77 million colors, suitable for storing natural images such as photos.
**Variable compression rate: **Users can adjust the compression rate to choose a balance between image quality and file size.

Cons

**Image quality loss: **Due to lossy compression, high compression ratio will lead to image quality degradation.
Repeated saving leads to quality degradation: JPEG images will be continuously compressed after multiple saves, and the image quality will gradually deteriorate (called intergenerational loss).
**No support for transparency: **JPEG does not support alpha channel (transparency) and cannot process transparent images.
**Poor editing tolerance: **Due to data loss during the compression process, it is not suitable for high-precision image editing.

Application Scenario

JPEG is widely used in the fields of photos, web images, digital content, etc. For example, photos taken by digital cameras and smartphones are usually saved in JPEG format. On websites, JPEG images are widely used to speed up loading. In the sharing of travel and event photos or the display of product images on e-commerce websites, JPEG can significantly reduce the file size while ensuring visual quality, facilitating fast transmission and loading. On the other hand, when transparent backgrounds or high-precision images are required, PNG or WebP formats are usually used. In scenes that require multiple editing or printing, TIFF or RAW formats are usually selected to avoid image quality degradation.