Scene Luminance Using Image Processing Toolbox?

I’m using the BLIP2 board and the Image Processing toolbox. Are there any functions to directly get the scene luminance from the image? Since luminance is often measured with the cameras on smartphones when lux meters are not available, I was curious if Analog Devices already has functions to measure this. While I know there are ways to calculate luminance as a weighted sum of the RGB values, I believe there would need to be some calibration involved. Has Analog Devices already done this calibration for their image sensors?

  • Hi Stephanie,

    If you are using the BLIP board you can directly obtain the output of the sensor in a luminance only format. You can use the  FrameCapture example in the BLIP board support package.  Modify the line in FrameCapture_ClassDriver.h

    #define CAPTURE_VIDEO_DATA_FORMAT ADI_VIDEO_IN_RAW422_PROG

    to

    #define CAPTURE_VIDEO_DATA_FORMAT ADI_VIDEO_IN_Y

    The corresponding output of the file will be in a luminance only format.

    Regards,

    Neeraj

  • Hi Neeraj,

    Thanks for pointing me towards to that example. There would still need to be some calibration to get the luminance of the scene as measured with a lux meter, correct?

    Thanks,

    Stephanie

  • Hi Stephanie,

    The Y or intensity value at that individual pixel would be a rough approximation of the total light intensity received at that pixel corresponding to light from a particular direction captured by the sensor. However since the sensor is optimized for occupancy detection, there will be processing steps like thresholding to remove low and high light artifacts, auto exposure, auto white balance. So this would not be a very precise measurement comparable to one you would obtain using a lux meter. Hope this helps,

    Regards,

    Neeraj

  • Hi Neeraj,

    Thank you for the quick response. So if I output the raw yuv 422 file, would I get y values without the processing, which perhaps would correlate much better to the luminance as measured by a light meter?

    Thanks,

    Stephanie

  • Hi Stephanie,

    The Y only output is derived from the YUV422 output. The complete processing is done by the sensor itself by the On-chip image flow processor and the processed image is the one output to the Blackfin processor. So I believe it would be independent of the format of data you extract.

    Regards,

    Neeraj