The Gugusse Roller software uses the PiCamera python library and with it, when we set the auto-exposure to off and/or the auto-white balance to off, we have apparent control over all settings for the camera.

It feels like having full control but it's not.

Somehow the first few seconds you start using the camera some registers auto-adjust themselves and keep having an effect until you stop using the camera.

So you setup an iso value, an exposure value, some white balance values but the effect will differ if the picture was dark or light(brightness), warm or cold(colors) on the first second you start using the camera.

It's something that I would really like to be addressed. It might be something I didn't understand in how to use that PiCamera library but for the moment I believe this is a disconnect, a misunderstanding, between the programmers of the PiCamera library and the programmers of the firmware of the cameras.

Because of this it's always better to start your scan on a colorless clear frame when possible, which is not always.