reference

Thermal Images

API reference | FLIR Thermal app

The labkit.thermal functions read FLIR radiometric JPEG files, expose their raw sensor data and calibration metadata, convert sensor values to degrees Celsius, and create display-ready RGB images. They can be called from MATLAB without opening a LabKit app.

Start Here

Use this sequence when you want to analyze thermal files in a script:

files = ["capture-01.rjpg", "capture-02.rjpg"];
[records, report] = labkit.thermal.readFiles(files, ...
    struct("SkipInvalid", true));

for k = 1:numel(records)
    temperatureC = records(k).temperatureC;
    fprintf("%s: %.1f to %.1f C\n", records(k).name, ...
        min(temperatureC, [], "all"), max(temperatureC, [], "all"));
end

fprintf("Loaded %d files; skipped %d.\n", ...
    report.loaded, report.skipped)

readFiles preserves the input order. With SkipInvalid set to true, it returns every readable record and describes unreadable files in report.failures. Without that option, the first read error stops the call.

Choose a Function

Thermal Records

readFile returns one structure with these fields:

An ordinary JPEG preview is not a temperature matrix. The reader looks for an embedded FLIR FFF RawThermalImage record and uses that sensor data for the conversion. A .jpg or .rjpg extension therefore indicates only a candidate file. Call inspectFile when you need to know whether the contents are actually readable as thermal data.

Temperature Correction

The default "environment" correction uses the camera's Planck constants and, when available, emissivity, object distance, reflected apparent temperature, atmospheric temperature, humidity, infrared-window temperature, and infrared-window transmission. Missing environmental values receive documented defaults so that conversion can continue. The five Planck constants never receive fallback values.

Use two outputs from rawToTemperatureC to see exactly what happened:

[temperatureC, diagnostics] = labkit.thermal.rawToTemperatureC( ...
    raw, calibration, struct("Correction", "environment"));

if diagnostics.usedDefaults
    fprintf("Defaults used for: %s\n", ...
        strjoin(diagnostics.defaultedFields, ", "))
end

diagnostics.parameterSources records "calibration" or "default" for each environmental input. A conversion that used defaults may be useful for previewing data, but the result is not evidence that the assumed emissivity, distance, humidity, or temperatures match the experiment. Check those values before using the temperatures in quantitative analysis.

Choose "planck-basic" only when you intentionally want the conversion based on the five Planck constants alone:

temperatureC = labkit.thermal.rawToTemperatureC(raw, calibration, ...
    struct("Correction", "planck-basic"));

Rendering a Temperature Matrix

renderImage maps a numeric matrix onto a colour palette. It does not change the temperatures and does not perform calibration.

rgb = labkit.thermal.renderImage(temperatureC, ...
    struct("Limits", [20 40], "Palette", "iron", "Levels", 256));
image(rgb)
axis image off

Values outside Limits are clipped to the end colours. Supported palettes are "turbo", "parula", "hot", "gray", and "iron". The FLIR Thermal app also offers display-only log and gamma controls; those controls are app features and do not alter exported temperature values.

Supported Files and Limitations

The current reader supports FLIR radiometric JPEG and RJPEG files with an embedded FFF raw-thermal record. Camera models and firmware revisions can encode metadata differently. Use inspectFile or readFiles with SkipInvalid=true for mixed or uncertain inputs, and retain the returned failure messages when reporting an unsupported file.

Do not infer measurement accuracy from successful parsing alone. Quantitative temperature accuracy still depends on the camera calibration and on correct environmental inputs for the photographed material and scene.

Reference Contract

Each generated Thermal API page distinguishes returned status from thrown errors and documents every implemented option, default, legal value, output field, and related function. Executable examples and package-wide public-help discovery prevent the manual and callable surface from silently diverging.

Related Topics

• Image functions cover ordinary image IO and image processing that does not use radiometric calibration.
• FLIR Thermal app provides interactive file review, measurements, display controls, and exports.
• Project history lists changes to thermal file support and calibration behavior.