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 easiness 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 and automatically stretched to the optimal brightness, flipped or rotated. Both scale, black and white point can be adjusted manually afterwards by the corresponding buttons in toolbar. You can anytime return to the automatic mode of the screen transfer function.
The file header and the image histogram can be viewed by clicking corresponding button in toolbar. You can view raw images in colour by selecting correct Bayer matrix offset.
Image can be exported easily to JPEG format with current black and white point setting.
The viewer is based on CFITSIO library and supports standard monochromatic and color FITS image formats.
To run FITS Preview you need Apple Mac running macOS Big Sur or later.