title: How to convert CCSprite to black and white/Gray using setBlendFunc
body: <p>Is it possible make a CCSprite to black and white one using setBlendFunc ? If yes please tell how to do it.</p>
  
  <p>More Details:</p>
  
  <p>I have to make my game sprite (background,character) to gray salce/black and white for a certain point of time. I dont want to take another image for this. I have tried CCTexture2DMutable. But the thing is it take extra memory of the same sprite. </p>
  
  <p>Is there any way to use one mask image and make all sprite to gray scale. 
  Please help.</p>