Open the image you want to add the effect to. Mine is this:

Now make a new document
, transparent background, 1×2 pixels.
Fill with black a pixel then go to Edit > Define pattern and call it whatever you want.




Now close the pattern document and go to the image.
Go to Edit > Fill And fill the image with the pattern you created.
Now you’re done.








This is used for making the effect for TV
http://www.photoshopnerds.com/images.