FITS to JPG Converter
FITS is the file format of astronomy and scientific imaging, and everyday viewers rarely open it. This converter reads a FITS or FTS image in your browser, stretches the data into the eight-bit range and saves a JPG. It is meant for looking at the picture and sharing it, not for measurement.
Embed this tool on your websiteShow code
Free to use on any site. Paste the code where you want the tool to appear. It runs inside the page; visitors' files are processed in their own browser and are not uploaded.
WordPress and most site builders have a "Custom HTML" block where this code can be pasted. The embed keeps a small link back to CalcMaster.
How to convert FTS to JPG
- Add your FTS files by dropping them, clicking the drop zone or pasting.
- The output format is already set to JPG. Adjust quality or size if you need to.
- Press Convert and compare the original and new size for each file.
- Download each file or all of them as a ZIP.
When to convert, and when not to
- You want a quick look at an image from a telescope or instrument without special software.
- You need a picture for a talk, a post or a note.
- You will keep the FITS file for analysis.
- Do not use the JPG for photometry or any measurement; scaling and compression change the values.
What changes
- Greyscale images and three-plane colour images are read, and the data is stretched to eight bits.
- Other three-dimensional data, such as a stack of frames, shows the first plane in grey.
- Rows are flipped so the picture is upright, as FITS stores the bottom row first.
- JPG is lossy and has no transparency, so values become rounded colours.
- Header keywords such as exposure or coordinates are not written to the JPG.
What the stretch does
FITS images can hold very large numbers and very small ones in the same frame, and a plain copy to eight bits would often show a black rectangle with a few bright dots. The converter therefore stretches the values between the dark and bright ends of the data so that detail becomes visible. The stretch is a display choice, and it is not the same as the calibrated pixel values.
Colour and greyscale files
A single plane becomes a greyscale picture. A file with three planes is read as red, green and blue and gives a colour picture. A cube with more planes, such as a stack of exposures, is not turned into a combined image; you see the first plane in grey. Combine or split such data in a scientific tool first.
Complex files
Scientific FITS files can be complicated, and a viewer made for astronomy will always show more than a general converter. Use this tool for a quick, shareable picture, convert one file first and check what you get before you run a batch. It also helps to open the picture beside your original in a FITS viewer.
Keep the FITS for science
The JPG holds rounded eight-bit values and compression noise. It is good for a slide or a web page and wrong for any calculation. Keep the FITS file as your data.
Preparing images for sharing
A FITS frame straight from a camera often shows little at first glance. After the converter's stretch you may see a clear star field or a faint nebula. For a post or a talk, check the result at full size, crop in an editor if needed, and credit the source of the data. The JPG is for presentation; it does not replace calibrated processing in your usual astronomy tools.
Large frames
Survey and camera frames can be very big. If the browser struggles, reduce the size with the resize option or convert one frame at a time.
Privacy: your files stay on your device
- The tool decodes, resizes and encodes your pictures with your browser. The files are never sent to a server.
- To check it yourself: open the browser developer tools (F12), open the Network tab, convert a file, and look for any request that carries your image. You will see none.
Frequently asked questions
Why does my picture look different from my astronomy software?
The converter picks its own stretch between the dark and bright ends of the data. Astronomy programs offer many stretches and may start with another one.
Can I convert a colour FITS?
Yes, when the data is stored as three planes. It is read as red, green and blue.
Why do I only get one frame from my cube?
Data with more planes is not combined. The first plane is shown in grey.
Is the JPG suitable for measurements?
No. Scaling and compression change the values. Use the FITS file for measurements.
What is the difference between .fits, .fit and .fts?
They are extensions of the same format. The converter accepts all three.
Why does a colour FITS look tinted?
The three planes are read as red, green and blue as they are stored. If the file was made for later calibration, the balance may need adjusting in an astronomy tool.