Thanks fkeel!
@ NietGiftig
If you are using my code, you should be able to see the values in processing itself (the numbers being continuously printed at the black potion in the bottom of processing) Something of that sort (weak colors, not totally dark when black screen) happened when I initially used the non-PWM pins accidentally. Also happened when I didn't ground pin 8 of the ULN2003A chip (should be connected to ground of 12V power supply and also Arduino GND pin). Also, remember that since you changed the resolution you should also change the numbers you divide the total by when averaging.
r=r/(684*464); //average red (should change to r=r/(950*540) )
g=g/(684*464); //average green (should change to g=g/(950*540) )
b=b/(684*464); //average blue ((should change to b=b/(950*540) )
I hope this will solve the problem because I think LED strips functions more or less the same.