Problem with Black Levels and Micro Converters

So i have a rather big problem which is the following:

The Source is a PC or Console which is sending a Signal through an HDMI Splitter -> HDMI-SDI Micro Converter-> ATEM 4k and then captured with BM Media Express.

With this we have a huge shift in the black levels as u can see in the attached file

Does anyone got an idea where this shift could come from? We already tried it with JUST the HDMI-SDI Converter but the problem still occured.

Kind Regards

My guess: You got a conversion from RGB to Y'CbCr somewhere in your chain; either because your PC negiotiated one with the converter (over HDMI), or because the converter did it yourself. (SDI is generally 4:2:2 Y'CbCr whereas PC output is typically 4:4:4 RGB, although there are exceptions.) In the process, I guess something mixed up limited vs. full range Y'CbCr; ie., the Y'CbCr signal was sent as 16–235 but interpreted as 0–255. This means not only black level is off, but also white level.

Any way of outputting ycbcr from a PC?

It will vary with the GPU, the drivers and the OS. NVIDIA can send Y'CbCr from most cards, I'm fairly certain; less sure about e.g. Intel.

With NVIDIA this is pretty simple, see attachment.