title: block image detection
body: <p>i want to detect color from a pixelated image, and then, turn the specific pixel into different color?</p>
  
  <p>for example:
  pixel with B/G/R &lt; 150 re-color it to white. and pixel with B/G/R > 150 to black or stay.</p>
  
  <p>is it possible? if yes, how? i need guidance. </p>