PNG

The Portable Network Graphics (PNG) format is designed to support general raster graphics as a replacement for the Graphics Interchange Format (GIF). This format is used mainly for graphics on the Web. With geospatial images, PNG can be used because of its good compression techniques.

GDB supports grayscale and color images. Palette images are expanded to three-channel red, green, and blue (RGB) images.

GDB supports reading and writing of PNG files. One or three 8-bit unsigned (8U) or 16-bit unsigned (16U) channels can be written.

When a PNG file is created, transparency is controlled by using an alpha band or the NO_DATA_VALUE metadata option for each band. When a PNG file is read, the alpha band is stripped out and transparency is controlled by the NO_DATA_VALUE metadata option of each band.

Gamma and chromaticity information is ignored. No other metadata is supported. Interlaced files are not supported.

PCI Geomatics acknowledges the Open Source libpng for its support of the PNG format.