It depends on what you want to do. Intensity is defined as Power/Unit area. So, to measure an average intensity you measure an area and a power. Since ImageJ only works with images, you must find some way to convert between pixels and length, and pixel counts and power. Thus, you must calibrate your image with a power meter and a ruler or other length standard.
Now, if you are new to imaging, you probably do not need a calibration trail, as you would for scientific measurements. You probably just want to know what the number of counts are at a certain pixel. The easiest way is to zoom up to the area you want, and put the cursor over the pixel, and the pixel count will appear in the ImageJ window. Alternately, you can use ctrl-m to get a more specific numbers for a region of interest, or ctrl-h to get a distribution of intensities.
Finally, you should probably read the imageJ manual, or check out the many books and websites on imaging that exist. Combine those with experimentation and you will learn much more and much more quickly than any message board will give you feedback.
reddi wrote
Hi I am new to imaging and would need some help in calculating the image intensities using ImageJ software. Please help me by telling how to calculate image intensities.
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