How to Measure Fluorescence Intensity in ImageJ

April 29, 2026

Measuring fluorescence intensity is a core quantification task in cell biology. ImageJ provides precise tools for this, but the workflow has several steps — especially when accounting for background with Corrected Total Cell Fluorescence (CTCF).

The Manual Method

1. Open your image

Go to File → Open. Work in a single channel (split channels via Image → Color → Split Channels if needed). Use 16-bit or 32-bit images for best precision.

2. Set your measurements

Go to Analyze → Set Measurements. Check: Area, Mean gray value, Integrated density, Min & max gray value. Click OK.

3. Select a region of interest

Use the Oval or Freehand selection tool to draw around your cell.

4. Measure the ROI

Press Ctrl+M or go to Analyze → Measure. A row is added to the Results table with area, mean intensity, and integrated density.

5. Measure background

Select a cell-free region using the same tool. Press Ctrl+M again.

6. Calculate CTCF

CTCF = Integrated Density − (Area of cell × Mean background intensity)

Compute this in the Results table or export to a spreadsheet.

Measuring Multiple Cells with the ROI Manager

1. Draw an ROI, press T to add it to Analyze → Tools → ROI Manager.
2. Repeat for each cell.
3. Select all ROIs in the manager and click Measure.

ImageJ Macro for Batch Fluorescence Measurement

dir = getDirectory("Choose folder");
list = getFileList(dir);
run("Set Measurements...", "area mean integrated min display redirect=None decimal=3");
for (i = 0; i < list.length; i++) {
    open(dir + list[i]);
    run("Select All");
    run("Measure");
    close();
}
saveAs("Results", dir + "fluorescence_results.csv");