0

What is the best way to find the intrinsic parameters of a Digital Camera? I have tried using the opencv Camera Calibration tool but it gives me different values after every calibration. So Im not sure if it is correct or not. Whereas the same method works perfectly fine for a USB camera.

I am not sure if the process to get intrinsic parameters for digital camera is slightly different and if im missing something.

If someone has any clue regarding this... please help!

vacky
  • 277
  • 1
  • 4
  • 16
  • 2
    USB cameras are digital cameras... what do you mean with different values? ±1% or ±2000%? the results of your calibration shouldn't be too different. you can simply average multiple calibrations. if they are very different you should check your calibration setup. maybe you're doing something wrong. – Piglet Dec 14 '17 at 08:16
  • 1
    Watch your lens. Are you auto-focusing or auto-closing a lens iris? Both affect the calibration parameters. Perhaps your procedure is inadequate? See this other answer for more: https://stackoverflow.com/questions/12794876/how-to-verify-the-correctness-of-calibration-of-a-webcam/12821056#12821056 – Francesco Callari Dec 14 '17 at 08:20
  • @Piglet Sorry if my terminology is wrong. By Digital camera I meant something similar to a Sony A7R2. The values differ by about +-60% – vacky Dec 14 '17 at 15:30
  • @FrancescoCallari I am manually setting the focus to a specific value and I keep it constnt throughout the calibration process. I am not sure how to check if the lens iris is auto-closing or not. Will look into that. And thanks for referring that answer – vacky Dec 14 '17 at 15:33
  • 1
    I guess if you want any help you should provide more detail on what you're actually doing. 60% is definitely too much deviation for a presumed fixed focus/f-stop system. maybe add some pictures, sketches. provide your code and parameters – Piglet Dec 14 '17 at 15:42
  • Thanks for helping me spot my one mistake. I did not keep the f-stop fixed during the calibration process. Does change in ISO and White balance will affect the calibration? – vacky Dec 14 '17 at 16:09
  • @FrancescoCallari Does change in ISO and White balance during the process of calibration affects the calibration results? – vacky Dec 14 '17 at 16:29

1 Answers1

1

Changes in ISO and white balance happen "behind" the lens+sensor combo, so they cannot directly affect the calibrated geometry model of the camera.

However, they may affect the results of a calibration procedure by biasing the locations of the detected features on whatever rig you are using ("checkerboard" or similar) - anything that affects the appearance of grayscale gradients can potentially do that.

The general rule is: "Find the lens and exposure settings that work for your application (not the calibration), then lock them down and disable any and all auto-gizmo features that may modify them". If those settings don't work for the particular calibration setup you are using, change it (for example, dim the lights or switch the target pattern to gray/black from white/black if the application lighting causes the target to be overexposed/saturated).

Francesco Callari
  • 11,300
  • 2
  • 25
  • 40