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D435i rgb cam: relation software gain to sensor gain

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Maik Wischow
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Dear all,

I am currently working with the D435i RealSense RGB cam in raw mode and trying to figure out how the software adjustable gain (anything between 0 and 128 ... db?) relates to the actual gain of the camera sensor (OmniVision OV2740). I assume there is some mapping. 

The only clue I found was in the source code of the SDK:

https://github.com/IntelRealSense/librealsense/blob/3371f4d6c80f37ccae1491d16f41b039f2049396/include/librealsense2/h/rs_frame.h (line 35)

RS2_FRAME_METADATA_GAIN_LEVEL , /**< A relative value increasing which will increase the Sensor's gain factor. \

Unfortunately, I can't get any further than this.

Does anyone have any ideas?
Thanks in advance and best regards.

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  • MartyG

    Hi Maik Wischow  There is limited documentation available about the functionality of RGB gain.  My research of your question established the following facts.

     

    *  The RGB gain (0-128) sets the amount of gain that is applied to the frame if auto-exposure is disabled.

     

    *  As you mentioned, the unit of gain is the Decibel (db).

     

    *  It takes a couple of frames for the camera firmware to register gain change and an additional 60-120 ms for the frames to get back to the algorithm.

     

    *  The image below demonstrates how an RGB image is affected when gain is set at 0, 64 and 128.

     

     

    If more detailed technical information is required about the OmniVision OV2740 sensor then customers with an Intel non-disclosure agreement (NDA) can submit a ticket to Intel on the Zendesk support channel.

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  • Maik Wischow

    Hi MartyG ,

    Thank you very much for your fast response!

    Do you know whether there is any non-linear post-processing applied to the images after the gain amplification? I am afraid I have to dig a little deeper and will consider the NDA then. Thanks anyway!

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  • MartyG

    As far as I am aware there is no post-processing (processing that is calculated on the computer's CPU instead of on the camera hardware) that is applied to images as a consequence of changing the gain value.

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