MAST image file format (IPX)
An IPX image file format was developed in 2003 and has been used since then as the main format for MAST images [1]. A number of standard image formats existing at that time could not satisfy requirements for effective and universal storage of image sequences produced by fast CCD cameras. For example, the most suitable candidate (TIFF) stores each image as a single entity; that means all meta-data common for the sequence must be repeated in each frame. Moreover, TIFF supports only “Zip” compression which is ineffective for images, and an additional license is required for access to compressed files in IDL (main analysis tool on MAST). The IPX file is a simple container for image sequences; it contains a file header and one or more frames. The file header contains all common meta-data, camera settings for example. Each frame has a frame header with frame-specific information. The image data is stored in the frame as raw data or as a compressed file using JPEG2000 codec. The IPX file is specialized for image sequences produced by one camera; that means all images in the file must be similar: they have the same size, depth, and other meta-data. The first version of IPX format has binary headers: both file and frame. Rapid progress in CCD cameras made this version obsolete; it was not flexible enough. The second version of IPX format has a flexible text header both for the file and for each frame. The meta-data can be placed either in the file header or in the frame header. For example, the image exposure can be common for all frames (put in the file header) or different (put in the frame header). IPX2 can also store up to three reference frames: bad pixel table and two non-uniformity correction frames. A number of file access and transformation tools have been developed including graphical viewer (ipxview) implemented in Windows and Linux. All tools support both versions of IPX format.