Poor image quality

[pczao]

Hello,

I'm new to Android HU.
I have bought a MTCC-KLD6-V2.91, RK3188, 1024x600, running stock Android 5.1.1.
Image quality is not good, it's like a very compressed JPEG, with noise around text, poor gradients/shadows on movies.
Is that normal for this type of HU. Do you know what can cause this?

Attached is an example taken when using Play Store, highlights in the noise.

 

[pczao]

I've uploaded a video on Youtube but I'm not allowed to post the URL.
Here is an image of a gradient. It was supposed to be smooth, but it's all crappy, bad quality.
Anybody?