Whats gone wrong?

Whats gone wrong with the background of this picture i have not got a clue

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Over compressed would be my guess. Is it like that in the original full size pic or did it only do that after downsizing and saving?

It's posterization. Looks like you did a lot of color manipulation in post processing. Right?

-js

Posterization

I did increase saturation a bit and the original is fine

tongard wrote in post #5465544
I did increase saturation a bit and the original is fine

Ah. The ol' crystal ball still works!

Yes, saturation increases must be done with restraint when you have a color gradient like your background or blue sky.

The image looks unnaturally saturated to me, but if that's the look you want you have some options.

Since the foreground looks good, you could (starting over with the original) increase the saturation moderately so the background still looks OK, then select the foreground and apply more saturation to the selection.

Experiment a bit - it's fun. Post your results, too...

-js

Crank down the saturation in the green channel and you should be ok. Check your histogram when you shoot to make sure you don't blow out or oversaturate any of the channels, and nail your white balance, and all should be well again.

Use LAB mode instead of RGB mode to increase saturation and the pic will be fine.