Nvidia 2080ti GFX output modifies pixels?

I am developing a display port capture device, I am trying to capture the display port output from the 2080TI GFX card.
I am using Ubuntu 18.04 with the 440 drivers. The resolution I am trying to capture is 3840x4320.
I have setup an 3840x4320 bitmap as the background for linux. On the secondary DP output, I have the resolution set to 3840x4320, so the background image is fullscreen. Now I capture this image, but the image is not identical to the bitmap I have set for the background. I have disabled the “dithering” and “antialiasing” options in the nvidia-settings application. The image looks visually identical to the bitmap used as the background, but if you compare pixel by pixel it is different. I do not think it is a signal integrity issue because the image I capture is always the same. Also the values of each individual pixel when they are different may differ by 1 or so. If it was a signal integrity issue, I would expect random bits to be different, or the CRC of the static image I capture would change.
Is is possible the 2080TIO GFX is doing some kind of “on-the-fly” processing and changing the pixel values slightly when displaying? How can I be sure the 2080TI outputs the exact pixels of the background bitmap unchanged?

Does anyone at Nvidia have any comment for me?
Thank you.