FITS Preview is a lightweight and fast viewer for images in FITS format (Flexible Image Transport System) introduced by NASA and HEASARC.
In comparison with any full feature FITS editor, it offers unbeatable overall speed and ease of use. Just double-click on any FITS image in any folder and the FITS Preview application will open it in a fraction of second, automatically sized to fit the window, automatically stretched to the optimal brightness, and flipped or rotated. Scale, black point, and white point can be adjusted manually afterwards using the corresponding buttons in toolbar. You can return to the automatic mode of the screen-transfer function at any time. The file header and the image histogram can be viewed by clicking the corresponding button in toolbar. You can view raw images in color by selecting the correct Bayer-matrix offset.
Images can be exported easily to JPEG format with the current black- and white-point settings. The viewer is based on the CFITSIO library, and supports standard monochromatic and color FITS image formats.