Convert fits to gif Online: fits2gif

You can use Tom's Editor to easily convert images from
Flexible Image Transport System .FITS to CompuServe Graphics Interchange Format .GIF.
Tom's Editor is a free, online image manipulation and converter program.

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FITS

Flexible Image Transport System is an image format with extension FITS.

GIF

GIF images were created by Compuserve. They can used no more than 256 colors and a single color transparenty (no Alpha channel). Today are rare since they offer low quality and huge filesizes. GIF animations are still in use.