I didn't  know you were saving your renders as .jpg files.

I agree that it's always better to save them as .png files and then use your graphic program to save them as .jpg files where you have more control over the compression of the image.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi