Samsung Galaxy S4 — Glitch with Dark colours! (Need Help)

I recently bought S4 I9505, its indeed a great phone but theres a little glitch...
Images with black or dark purple (or any dark colour) background aren't clear. Like in night i took a picture by front camera, on camera it was ok but after taking the picture, it got so pixel-ed or i dont know what to say..
similarly that purple live wallpaper doesn't have that good graphics.. moreover if a friend sends me any such pic, it doesn't have as good resolution as the real one. similarly when I sent my that dark pic to computer, it was ok... but on my phone these images doesn't look clear..

(Games work fine! even when they are dark)

im so annoyed by it.. i checked display settings and everything but nothing could help me..
I cant even use effects of Camera other than Normal(Auto) as the screen gets soooooo dim and uncleared and pixel-ed ... hope I explained it completely ?

what to dooo???? please help anyone!!!