FITS Preview is a streamlined viewer specifically designed for images in the FITS format (Flexible Image Transport System). This format was introduced by NASA and the High Energy Astrophysics Science Archive Research Center (HEASARC) to facilitate the robust transmission and manipulation of astronomical data.

Unlike comprehensive FITS editors, FITS Preview stands out for its speed and user-friendliness. The application is tailored for users who need quick, efficient access to view their astronomical images without the overhead of complex editing features.

The viewer's ease of use is highlighted by its straightforward functionality: a double-click on any FITS file across various directories prompts FITS Preview to open it instantly. The application automatically adjusts the image to fit the viewing window and optimizes brightness, while also allowing for adjustments in image orientation as needed.

Additional features of FITS Preview include the ability to view the file header and the image histogram, which are essential for analyzing the data contained within the images. Users can also view raw images in color by selecting the correct Bayer matrix offset, thus enhancing the visual data interpretation.

FITS Preview is based on the CFITSIO library, supporting both standard monochrome and color FITS image formats. This compatibility ensures that FITS Preview can be used seamlessly within various astronomical data analysis workflows, providing a reliable and efficient tool for image viewing and preliminary data assessment.

In addition to FITS format it supports also XISF (introduced by PixInsight, 8 and 16 bit-depth only) and INDIGO Raw (introduced by INDIGO Initiative).