The gradient in background image is discrete. It has thick lines of the same color, followed by lines of different color, that is clearly distinguishable from the first one. And so on.
Steps to Reproduce:
Open http://techbase.kde.org/ or http://userbase.kde.org main page. Look at the background right side, near the letter «n» in the big word «information».
I can see the lines, they are distinguishable.
The lines should be indistinguishable, the gradient should be smooth.
Dell U2211H, xf86-video-ati, default settings.
Created attachment 61572 [details]
This is not a bug, but unfortunately a JPEG artifact. There is no way to remove it, unless the background is removed and replaced with a single color. Converting to any other format is not an option as well, since JPEG is by far the least in file size. An equivalent PNG would easily go over a few MB in size, which is unacceptable.
That does not look like jpeg artifact. But if it is, it is still possible to play with compression level.
Jpeg artifacts generally produce squares. But this looks like just gradinent with wide stripes.
The stripes are caused by the fact that the colors are limited (see attached image, the colors are as close as they could be), and the gradient just can't be smooth because of that (it is wider than the number of colors between the start color and the end color).
Tere are different techniques to avoid such lines when making gradinents, like so: http://groundice.com/notes/gradient.php (russian, but just looking at the images should be enough).
The first two images are the example of the problem (1-st is with slighly raised contrast, the second with largely raised contrast).
The third one it dithering workaround (not so good).
Next images show noise+blur workaround (the better one, but still not ideal).
Created attachment 61644 [details]
Bad gradient demo.
This gradient is striped as a result of limited colors.
No artifacts, just simple 900px wide „gradient“ from #808080 to #858585, producing 6 stripes each 150 px wide.
The stripes are visible for human eye.
I speak, read, and write Russian very well :) I am also well acquainted with different diffusion techniques. Problem here however is that we are not dealing with a simple gradient, we are dealing with a gradient in a webpage background, where the file size is a paramount. Any sort of diffusion I could choose will greatly reduce the efficiency of JPEG compression based on similarities in tint and luminosity (and that's where those broken gradient stripes come from - they are of the same luminosity and therefore get extrapolated).
The background is 1597 × 1053 in physical size and that's a LOT of pixel mass. At this size with given compression it is a whooping 105KB in size. Making it any sharper will jump the file size up to 300KB and over which is unacceptable for a webpage background.
Hope this answers your questions.
The default theme was changed to Neverland.