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OPT8241-CDK-EVM: OPT8241 Voxel Viewer pixel wise calibration how to do it

None_feiyu
Expert 1320 points

Part Number: OPT8241-CDK-EVM

Dear TI,

         I want to know more about the piexl wise calibration,what is the principle?

         pixel-to-pixel variation map how affect image quality? I am very confused.

         look forward your answer.

         Thanks&Regards.

          None

  • 0
    TI__Expert 3495 points

    Pixelwise calibration works hand-in-hand with Common Phase offset calibration. Consider the calibration setup below:

    Common offset calibration establishes a point-of-correlation 0_,0_ for center pixel. Once is found, the radial depth of each pixel is determined by:

                       


    0_ for the image center is what should be programmed into phase_corr_x. Once programmed, all pixel reading will has this offset automatically subtracted.

    Note that if d0_i is known, if lens is properly calibrated for distortion, non-center pixels d_i can be estimated by geometric calculation, and from this estimated distance, expected raw phase can be computed by:

                    

    Pixelwise calibration computes the difference between actual raw phase against the above estimated raw phase value.

    -Larry

     

  • 0 in reply to Larry Li
    Expert 1320 points
    Dear Larry,

    I will do explain about some nouns ,I want to know whether correct or not .

    C:optical center;
    f: focal length；

    η eaqul to pi?

    what does mean about η,d0i,ψ0i? Can you tell me ?

    Thanks&Regards.

    None
  • 0 in reply to None_feiyu
    TI__Expert 3495 points
    Optical center is center pixel position after lens calibration (cx, cy)
    f is lens' focal length. It is generally neglegible compared to the max range of your TOF camera.
    η is 4095 (12-bit representaton of 0-2*pi range)
    d0i - offset calibration distance of pixel i as measured from the TOF camera origin to the point in the scene imaged by pixel i.
    ψ0i - raw phase of pixel i measured at d0i.

    -Larry
  • 0 in reply to Larry Li
    Expert 1320 points

    Dear Larry

              Thanks for you reply.

             I feel doubt about the Optical  center & focal length.

             if c:light of speed; f:modulation frequency,This formula it seem like right?

            d0= c/(2pi*f)*ψ0---------------(1)

            di= c/(2pi*f)*ψi-----------------(2)

            formula(2)-formula(1)=

            di-d0=c/(2*pi*f)*(ψi-ψ0)---------(3)

            di=c/(2*pi*f)*(ψi-ψ0)+d0. 

            

           I hope to receive your answer,thanks.

  • 0 in reply to None_feiyu
    TI__Expert 3495 points
    Unambiguous distance is d_max = c/(2*f). The phase is proportional to distance over the 2*pi range, so:

    d = d_max * (ψ/(2*pi))

    so your formula (1) and (2) should be

    d = c/(4*pi*f) * ψ

    Offset calibration is needed is because at actual distance of 0, the ψ reading is non-zero due to systemic offsets.
    This is like finding the y-intercept of a line. Since calibrating at d0i = 0 is impractical, you can calibrate it at a longer distance and record a different phase offset.
  • 0 in reply to Larry Li
    Expert 1320 points

    Dear Larry,

              Thanks for you information.

              I understand why you need to do Offset calibration,but i don‘t understand this formula with f: (focal length) &c(optical center).

              

  • 0 in reply to None_feiyu
    TI__Expert 3495 points

    Don't confuse the 'f' in the FOV picture and the 'f' in the formula. The first is focal distance. The second is modilation frequency. 'c' in the above formula is speed of light.

  • 0 in reply to Larry Li
    Expert 1320 points

    Dear Larry,

            Fov figure is a bit misleading me， just you said  in the  formula ,c:speed of light,f:modunation frequency. 

            

           So when I do the pixel wise calibration mustt have to use this  formula.

           Can you give me example one by one to do manual calculation about the pixel wise.

           thanks&regards

           None

  • 0 in reply to None_feiyu
    Expert 1320 points
    Hi Larry,

    Can you give me more information?

    looking forward to your reply.

    thanks&regards.

    None
  • 0 in reply to None_feiyu
    TI__Expert 3495 points

    None,

    Both common phase offset and pixel wise offset are done for you in VoxelViewer as part of the calibration tool.

    See Section 4 of VoxelViewer user guide for step-by-step instruction.  

  • 0 in reply to Larry Li
    Expert 1320 points
    Hi Larry,

    I know it can do by VoxelViewer,But I want to know its principle and how to manually calculate it?

    thanks&regards.

    None
  • 0 in reply to None_feiyu
    TI__Expert 3495 points
    None,

    The calculations are described both in my post in this thread and also in the VoxelViewer document. For me to help you perhaps you could first write down the calculations you do understand and we can go from there?

    -Larry