FITS format
FITS stands for Flexible Image Transport System, and this format is what professional astronomers use for image data. FITS images consist of a plain text header and the binary image. The header contains at least information about coordinates of the image, but may also contain a slew of other things about, for example, the target of the image, the telescope which took it, the astronomer(s) who observed it, when it was observed, the wavelength used, and any data reduction steps that may have been done to the image. The binary image can be one plane or many planes of images. It can also be a table of data.
Astronomers use FITS images because they are at least 16 or even 32 bits deep -- that is, there are at least 2 to the power of 16 (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle 2^{16}} ) or 65,536 and possibly (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle 2^{32}} =) 4.3 billion possible discrete levels of data for each pixel. Things like jpegs or gifs are only 8 bits deep, meaning that there are only (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle 2^{8}} =) 256 discrete levels of information for each pixel (per color plane). This is why if you make a nice image in Leopard with lots of extra detail, that detail gets lost when you save it as a jpeg. The computer is compressing 65,000 levels into 256.
More information on FITS format
This issue also affect anyone who creates graphics on computers, not just astronomers. More information on bit depth and file format in the context of graphic design, and graphics for the web
