PNG (Portable Network Graphics)

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

PNG (Portable Network Graphics) is a commonly used image file format that is also widely used in GIS. It is a lossless compressed bitmap image format designed to replace the older GIF format. It supports 256 colors and transparency, and can be edited and saved multiple times without losing image quality. PNG files can store high-quality images with small file sizes and good image details.

File Structure

File signature: The first 8 bytes, fixed value used to identify PNG files.
Data blocks:

IHDR: File header, containing basic image information (such as width, height, color type, etc.).
PLTE (optional): Palette, only relevant to indexed color images.
**IDAT: **Image data, storing actual image information.
IEND: End of file marker.
Other auxiliary data blocks (such as bKGD, cHRM, gAMA, etc.) are optional and provide additional information (such as background color, physical pixel size, etc.).

PNG files organize information through data blocks. Key data blocks ensure basic file functions, and auxiliary data blocks provide additional functions and information.

Pros

**Lossless compression: **PNG uses a lossless compression algorithm, which can effectively reduce the file size while ensuring image quality. This feature makes the PNG format very suitable for saving digital images that need to be edited repeatedly, such as application interface elements, logos, and illustrations.
Support transparency: The PNG format supports the Alpha channel, which can achieve semi-transparent or fully transparent effects of images. This feature makes PNG widely used in fields such as web design and UI design, and can seamlessly integrate irregular-shaped images into the background to enhance visual effects and user experience.
**Rich colors: **PNG supports 24-bit true color and 8-bit grayscale images, which can present rich color effects and meet image requirements in various scenarios.
**Good cross-platform compatibility: **The PNG format is widely supported in modern browsers and can be directly opened and edited in most image editing software, with good cross-platform compatibility.

Cons

**Large file size: **Because PNG uses lossless compression, its file size is usually much larger than the lossy JPEG file under the same conditions. This means that for users with limited storage space, saving a large number of PNG images may not be the best choice.
**Not suitable for storing photos: **The PNG format is more suitable for storing images with transparency or flat colors, rather than complex photos. For applications that need to store high-quality photos with a small file size, the JPEG format is usually more suitable.
**No support for multi-image files and animation: **Compared with the GIF format, PNG does not support multi-image files and animation files. If you need to store animation or a series of images, GIF or other formats may be more suitable.

Application Scenario

In GIS, PNG format files are often used to store maps and charts of geographic data. It can contain geographic features, labels, symbols, etc., used to represent features and information on the map.