NIH Image

Use this dialog box to calibrates to a set of density standards, such radioactive isotope standards or a calibrated optical density step tablet (available from Kodak). Before calibrating, you must record the mean gray value of each of the digitized standards. First, use the Reset command to set the measurement counter to zero. Then use one of the selection tools and the Measure command to record the mean gray value of each of the standards. Note that the standards must be measured in order, starting with the lowest gray value (lightest) standard. 

When you have finished making the measurements, select Calibrate to display the calibration dialog box. To calibrate the image, enter the actual values in the Known column, select a curve fitting method, enter the unit of measurement, and click OK. If the calibration curve is not satisfactory, bring up the Calibrate dialog box again and select a different curve fitting method.