How jpeg compression affects image quality

Especially with the red channel!!

This is a photo originally taken in JPEG. Resized in Photoshop and save-as low compression (quality =9 or 10) JPEG:


Now see how it happens with save-as high compression JPEG (quality =4):


Blow-up the two files to 400%, and directly compare the two file side-by-side (Left: high compression / Right: low compression): Click on the image to enlarge it


You can see how a high compression distroy the details in the red color, and how it introduce artifects to the image.