False-Color Spectrum Mapping Tool: Map Grey Values to Colour, Free & Online

Use this free false color spectrum mapping tool in your browser. No sign-up, no download and no upload: everything runs on your own device, so your data stays private.

What this tool does

Grey images hide small differences that colour makes obvious, which is why false colour is standard in astronomy, remote sensing and microscopy. This tool maps each grey level of your local image through a colour map, jet, hot, viridis-like or plain grayscale, on a canvas in your browser. The mapping is a display choice, not new data, and the caption should say which map was used.

How to use it

Paste or type your local image and colour map in the box above.
Adjust any settings, such as cutoffs, scales or styles, to match your data.
Click the run button and read the output below the tool.
Check the summary numbers before you copy anything into a document.
Copy the output, code or image into your figure, slide or report.

Worked example

Use the demo black-to-white gradient with the jet map. The gradient becomes a rainbow from dark blue through green and yellow to dark red, and a faint step in the grey becomes a visible colour boundary. Switch to hot and the same gradient turns into black-red-yellow-white, like a heat image.

Tips for better results

Name the colour map in the figure caption; an unnamed rainbow map misleads readers.

Honest limits

False colour can exaggerate or invent boundaries at map transitions, so always keep the original grayscale beside the coloured version.

Choosing the right settings

Start with the default values. They are chosen to show a sensible result at once, so you can see the layout before you touch your own data. Then change one setting at a time. Changing one thing at a time is the fastest way to learn what each control does, and it stops two changes from cancelling each other out. If the output looks wrong, check the input format first: a missing comma, a swapped column or a stray space causes most errors, and the tool reports what it received in its summary line.

Using the result in a figure

For a figure, keep the output simple. One message per figure, short labels, and a caption that states the method and the settings you used will serve readers better than a dense, decorated chart. If a journal or supervisor will see the result, note the tool name, the input values and any cutoff in your methods or caption, so the figure can be reproduced later. That habit also helps you: six months from now, the caption is the only record of how the figure was made.

Common questions

Do I need an account? No. The false color spectrum mapping tool runs entirely in your browser with no sign-up and no saved data.

Is my data uploaded anywhere? No. Your local image and colour map stays on your device, which is why the tool is safe for unpublished work.

Can I use the output in a paper or presentation? Yes. The output is yours to reuse; just check it visually once, note the settings in your caption, and credit the method, not the tool, in your references.

What if the result looks wrong? Check the input format first, then change one setting at a time. Most errors come from a missing comma, a swapped column, or a value outside the expected range, and the summary line under the tool shows what it actually received.

Try the false color spectrum mapping tool above with the sample data, then with your own. It is free, it needs no account, and it works in any modern browser.

When you reuse the result, keep a short record of the inputs and settings you used. A one-line note in your project file, such as the data pasted, the cutoff chosen and the date, is enough to reproduce the figure later. If a collaborator questions a number, that note lets you rebuild the exact output in seconds instead of guessing what changed.

Embed this tool on your website — free

Copy the code below to add this working tool to your own page. A small credit link stays with it — that’s all we ask.