I am doing a physics lab where I need to take photos of a light and the intensity of the light changes. I have the photos but I need to understand how to get the average wattage from the images. There are open CV examples of seen but they don't tell me the units of the output of the example.

  • $\begingroup$ When you say "photo", I assume you're talking about digital image from CCD sensor, rather than a silver halide emulsion. Calibration is going to be the big thing. Get your hands on a photospectrometer, if possible. Failing that, try to put a reference illuminator such as a known LED into each image, and measure distance to the illuminator, for inverse square law. You will need photos of reference sources before you tackle unknown sources. Also, EXIF tags from some cameras can help you with details like exposure, white level, and saturation. $\endgroup$
    – J_H
    Feb 8 at 19:56
  • $\begingroup$ @J_H what exactly do you mean by calibration? And how would I go about doing it? $\endgroup$ Feb 8 at 20:20
  • $\begingroup$ You didn't say "I am using silver halide emulsions", so I'm going to keep assuming you're talking about CCD sensor in a webcam or other digital photography. When I say "bulb" I refer to a tungsten filament clear glass incandescent light bulb. You can connect a 25 W or a 75 W bulb to 120 V 60 Hz mains, and observe its black body radiation, plus verify the I-V waveform. Photon flux continuously hits your sensor. The sensor clears itself with a momentary ground connection, then photons from bulb keep arriving, convert to charge, which sensor eventually measures. Callibrate that to bulb power. $\endgroup$
    – J_H
    Feb 8 at 20:28
  • $\begingroup$ @J_H well I am using a DSLR camera not a silver halide emulsion. Also I'm new to this and I have no clue what you said. I have photos taken when there is no light whatsoever can I assume that the wattage from those images would be zero? $\endgroup$ Feb 11 at 23:17


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.