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gui:analyze:calibrate

# Calibrate...

Use this dialog box to calibrate an image to a set of density standards.

Use this dialog box to calibrate an image to a set of density standards, for example radioactive isotope standards or a calibrated optical density step tablet.

Before using this command, use Analyze>Clear Results to reset the measurement counter and use one of the selection tools and Analyze>Measure to record the mean gray value of each of the standards. There is an example that shows how to calibrate to an optical density step tablet.

When finished making the measurements, select Analyze>Calibrate to display the Calibrate dialog box. To calibrate the image, enter the known standard values in the right column, select a curve fitting method from the drop down menu, enter the unit of measurement, and click OK. ImageJ will then display the calibration function.

If the calibration function is not satisfactory, bring up the Calibrate dialog box again and select a different curve fitting method.

Rodbard is a four parameter general curve fit function proposed by David Rodbard at NIH. The form of the equation is:
<latex>

 y = d + \frac{(a - d)} {(1 + (\frac{x}{c})_b )}

</latex>

Selecting Uncalibrated OD from the drop down menu causes ImageJ to convert gray values to uncalibrated optical density values using the function:

<latex>

Uncalibrated OD = log_{10} \frac{255}{PixelValue}

</latex>

You do not need to measure OD standards or enter known OD values to enable this feature.