How to calculate the original image quality?

I am working in Image Watermarking Area. Watermarked Image quality is test to the PSNR, the values like 56.72, 43.81. My Questions are 1. How to calculate the original image quality? 2. From which value to Minimum and Maximum, to the best value of image quality in terms of PSNR?

Thanking you

Answer 1

[Walter Roberson]

The original image quality is always 100% unless there is additional information given to say that it is not.

If my picture looks blurry it could be because what I wanted was the Tower Of London In A London Fog, so the blurred picture might be the right appearance for my purposes.

Answer 2

[Image Analyst]

Perhaps this might be of interest: Vision models for image quality assessment: one is not enough