lylejk wrote:
If you open the jpeg in GIMP, you will see a poster separation line in the sky that is not there if you view the jpeg in the browser. The snapshot shows that separation line (at least on my monitor; glad that it does or there would be mud in my eye; lol) but the actually saved jpeg does not. May not be an issue with CRTs but for the 2209wa e-IPS display that I use it shows quite clearly (again, see the snaptshot capture with the red pointer showing the poster line separation).

The posterization is visible on the plain JPEG in my browser (Firefox) on my laptop LCD screen, and once I have downloaded the file, it also shows in Gwenview and Okular (and of course in Gimp 2.6, but no more than in the other two). It is more visible if the angle of view is above or below the perpendicular.
If you use the Pointer dialog, you'll see that the bands correspond to an increment in the RGB values. If you want to make it less visible you have to blur the transitions by using spread noise (20-30px).