Question about FFT operator on FPGA

  • Hello,


    We received an inquiry from a customer.

    This inquiry is related to FFT on FPGA.

    Visual applets have FFT functionality, but there are no cases where we have applied FFT applications on our side.

    It is difficult to give a solution guidance to the customer.

    If you have an advice, please let me know.


    Camera : 18k Line scan camera (Full configuration 8tap8bit)

    Interface : Camera Link

    LineRate : 40KHz /sec

    BandWidth : 400MB/sec


    Is it processed in real time with Full bandwidth in Visual Applets?

    -. Raw image ->FFT(forward)->remove high frequency-> Inverse FFT result image(DMA)




    For the information.

    We have sample images(Raw image and FFT result image)

    FFT result image is after Inverse transformation (remove high frequency)

    The Images are confidential.

    So I can not upload images here .But If you need to images for check, we can send it by email.


    About FFT parameter.

    E5 ironman:

    Points (image width): {8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192}

    By using parameters, the operator can be configured to the number of points i.e. line width. The line width has to match with the number of pixel at the input.


    Does that mean that it only support up to 8k camera?


    Thanks.

    Best regards.

  • Dear Sangrae_Kim,


    To use the 1D FFT on a 16k line to remove high frequency you can simply split it into 2 8k lines, process it (FFT forward&inverse) and merge both results into a single 16k line again.


    As a good strating point you can use the following example:
    https://docs.baslerweb.com/liv…ntent/examples%20FFT.html


    Since you want to remove the high frequencies this is a valid approach afaik.


    Best regards,

    Björn

  • Dear Björn Rudde,


    Thank you for your update.


    I understand what you said but I am not fully understand how to use the FFT operator in Visual Applets.

    For example, in a VA simulation I want to implement a function that transforms the frequency space via FFT (Foward) and then removes some moire patterns, and then returns it to the image space via FFT (Inverse) like attached image.

    I am not sure if this can be done on the Visual Applets side.

    Thanks.

    FFT.JPG

  • Dear Sangrae_Kim,


    I made you a simple prototype design for line lengths of 1024 pixel.



    Inside of "FrequencyBoxFilter" you can specify two ranges of frequencies to remove - as you need to remove the positive and the negative frequencies.


    I hope this helps a little bit.


    Greetings,

    Simon

    Files

    • FFT2.va

      (13.94 kB, downloaded 1 times, last: )
  • Dear Sangrae_Kim,


    this is a real basic approach, maybe it would be usefull to use a

    small binomial filter (x-direction) after the box filtering to avoid the sinc-artifacts.


    I'm really curious about your results.


    Best regards,

    Simon

  • Dear Simon,


    For the information.

    We got similar results with your help.

    I simulated it with an image file on Visual Applets.

    The FFT results from Visual Applet were able to achieve results similar to FFT images processed on PC.


    Thank for your help.

    Best regards.

    Sangrae.

  • B.Ru

    Closed the thread.