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Original question:

TDA4VM: DCC Tuning flow

TDA4VM: Low light Images and Decompanding, Normalization

Dinesh bharathi
Intellectual 751 points
Part Number: TDA4VM

Hi,

I am working on a low light data and used the same decompanding formula that was used in the camera, the output was way darker and when i checked the data range in matlab 90% of the data was within the range of 0-700 of 2^12 data, which is exactly opposite of the decompanding formula we had, so it looks to me like while capturing Auto Exposure has maxed out on all the things and this is the data that camera was able to capture. 
And that resulted in a darker image in my end. 

So what i did I modified the decompanding formula to fit the low light data and things are better now,  when i feed the pipeline with day time images the same decompanding formula over exposes everything and all i see is a white image.,is it possible to have switch between decompanding in realtime ? to have multiple decompanding formula for different lighting conditions that can be shifted using a high level algorithm? or there is a way around this?

Or precisely can i normalize the pixel range to fit the display, just like how we do in matlab?


Regards,
Dinesh

  • 0
    TI__Guru 59010 points
    Dinesh bharathi said:
    90% of the data was within the range of 0-700 of 2^12 data,

    Is this 0~700 range in companded format or linear data?

    Dinesh bharathi said:
    which is exactly opposite of the decompanding formula we had,

    What is the opposite of the decompanding formula?

    Dinesh bharathi said:
    so it looks to me like while capturing Auto Exposure has maxed out on all the things and this is the data that camera was able to capture

    This is possible if your low light is very dark.
    What is the illumination level of your low light scene?

    Dinesh bharathi said:
    is it possible to have switch between decompanding in realtime ?

    Yes, it is possible, but you will have to do it smoothly to avoid sudden brightness changes.

    The simplest way is to modify "tivxVpacVissSetParamsFromDcc(...)" in "vx_vpac_viss_target_dcc.c".
    When "tivxVpacVissDccMapRfeParams(...)" is called, you may change the decompanding given lighting conditions similar to "tivxVpacVissDccMapFcpParams(...)".

  • 0 in reply to Gang Hua
    Intellectual 751 points
    Gang Hua said:
    Is this 0~700 range in companded format or linear data?

    Yes, This is companded data and companding knee point are:
    1024-1024
    1920-8192
    2816-65536
    3776-1048576

    Gang Hua said:
    What is the illumination level of your low light scene?

    Not exactly sure, all i can say is it was evening time. I Just have this data to assess anything for now. 


  • 0 in reply to Dinesh bharathi
    TI__Guru 59010 points

    Thanks for sharing the information!

    That is very dark condition and very low dynamic range for your 20-bit WDR sensor.
    In that case, you may use different decompanding as digital gain to get brighter output image.
    Current decompanding settings are good for much higher dynamic range scenes.

  • 0 in reply to Gang Hua
    Intellectual 751 points

    Also is there a way around this without touching the Decompanding for such low light data, like DC offset/wb block will help the normalization?

  • 0 in reply to Dinesh bharathi
    TI__Guru 59010 points

    Using WB is equivalent to applying digital gain.

    H/W has a lot of flexibility, but TIOVX S/W and DCC may not support it directly.