The rear camera picture of my iPhone 8 plus is very noisy and the photo appears like hand drawing and like cartoon with colors distorted. even in day light the noise is very evident and picture quality is far below than the same shot on my iPhone 6

I recently upgraded from iPhone 6 to iPhone 8 plus 64 GB for better camera. currently on iOS 11.1.2.

from first day could see obvious difference in the picture quality shot using rear main camera in all modes. the picture quality is very poor with too much grain and the lines are disorted, under day light. even the picture color seems disintegrated and like cartoon colors. tried to shot using third party App too, but the result is same poor. iPhone 6 photos when compared with my 8+, iPhone 6 pictures are far superior.

Tried all settings combination with and without HDR and live etc. restarted the phone, reset all settings, yet no improvement. is this known issued, if so appreciate if anyone can give solution. Thanks in advance.