FITS (Flexible Image Transport System) is the standard storage format for astronomy and a lot of scientific imaging. A FITS file holds pixel data plus text headers that describe the telescope, the exposure, the world coordinates, and dozens of other properties. Most photo apps do not know what to do with it.

Why does my FITS image look black when I open it?

FITS pixel values are raw measurements, not display values. A single frame can span from near zero to tens of thousands, so the useful range sits far above what a normal viewer shows. This tool rescales those values into the 0-255 range a screen can display, which is why the result suddenly shows structure you could not see before.

Do you keep the FITS headers?

No. A PNG has nowhere sensible to put keywords like RA, DEC, or EXPTIME. You get the picture, not the metadata. If you need the header values, use a viewer or inspector that reads FITS directly.

Which files can I send to this page?

FITS images (.fits) are the point of this tool. Ordinary PNG images work too, which is handy when you just want to rescale or re-encode a picture you already have. Files can be up to 40 MB. Table-only FITS files with no image array cannot be drawn, so they come back with an error instead of a blank picture.

Which tone setting should I pick?

Start with Auto. It sets the bright and faint limits from the actual pixels and usually gives the most readable result. Pick Normalize when you want to stretch the full range edge to edge, or Equalize when the mid-tones are what you care about.

The conversion runs in an isolated sandbox that is discarded afterwards, and the output is only ever shown back to you. There is no account to create and nothing is indexed.

Convert FITS to PNG online

A FITS frame that looks perfect in a science viewer can be completely unopenable everywhere else — no email attachment, no slide deck, no website wants a 2880-byte-blocked scientific file. This page turns a FITS file into a PNG, the format every device on earth already understands.

How to convert FITS to PNG

Drop in a FITS file (up to 40 MB). PNG input works too.
Choose a tone mapping if the default is not what you want.
Press Convert file and download the PNG.

Auto is the setting to start with. It reads the range your pixels actually occupy and maps that onto the screen's range, so faint structure survives without the bright core blowing out.

What you get

One PNG file: the same picture, rescaled to 8-bit colour and saved in a format any viewer, editor, or chat app can open. Width and height are unchanged, so the PNG lines up pixel for pixel with the original frame.

The FITS headers do not come along. PNG is a picture format, not a data container, so keywords describing the exposure, coordinates, or instrument are left behind. Convert the image, keep the original file for the numbers.

Why the preview needs stretching

A FITS array stores measured values, not colours. On a telescope frame the interesting pixels can sit anywhere in a range far wider than a display can show, which is why an unprocessed FITS image looks black, or looks like a white blob. The tone options here do that rescaling for you, and the difference between Auto, Normalize, and Equalize is mostly about what you want the eye to land on first.

When this helps

Putting an observation into slides, a paper figure, or a blog post
Sharing a frame with someone who does not have astronomy software installed
Checking a batch of exposures quickly without opening a full FITS viewer
Making a thumbnail of a FITS image for a catalogue or a website

Good to know

Only files with an image array can be drawn. FITS tables and pure-header files return an error rather than an empty image.
The output is always PNG. If you want JPEG or WebP, run the result through an image converter afterwards.
Very large frames are fine up to 40 MB; if yours is bigger, crop it to the region of interest first.