title: Looping through pixels in an image
body: <p>My project is to input an image into a canvas tag in an HTML page, and then loop through the pixels and RGBA values of the pixels. While looping through the red values,so every fourth value in the pixel, I want to log the position of the pixels that represent a white pixel. Now, I have the image loading down with some code I got from this blog, <a href="http://www.phpied.com/photo-canvas-tag-flip/" rel="noreferrer">http://www.phpied.com/photo-canvas-tag-flip/</a> . </p>
  
  <p>He has another post in which he gives some code on how to loop through the pixels and log the information I want to log, but I don't understand it, and I don't want to copy his code without knowing what it is I'm doing. So could anybody please either explain the method he's using or perhaps show me another way to do what he's doing? This is the link to the other post <a href="http://www.phpied.com/pixel-manipulation-in-canvas/" rel="noreferrer">http://www.phpied.com/pixel-manipulation-in-canvas/</a> .</p>