Most pop art pictures in the public’s imagination contain a photograph that has been reduced to only two tones, black and white, and then colored in, for example Andy Warhol’s Marilyn pictured below.
The best way to do this is to go Image > Adjustments > Threshold in Photoshop. Move the slider until you get the best result. See below the picture of Rihanna here:
Flat colours should then be added on layers above your black and white background. Set these layers to Multiply so that the black shows through. Pick no more than about four or five quite vibrant colours. It was quite good to get the background cyan in the above picture of Rihanna. More pop art images here.
However, other effects can be achieved by reducing a greyscale picture to four or five tones instead of just two. Go Filter > Artistic > Cutout and choose the number of tones you want. Then they can be coloured up by going Image > Adjustments > Hue/Satuation, checking the Colorize box, putting the Saturation back up to the middle point and playing around with the Hue. See George W Bush below.
I also added those little dots favoured by another famous pop artist – Roy Lichtenstein who’s famous “Whamm!” image you can see below:
To achieve this I had to add a “clouds layer”. Click the small black and white squares by the foreground and background color on your Tools palette to default the colours (or press D) and go Filter > Render > Clouds on an empty layer. This is a handy way to get something to play around with when you’re setting textures generally.
Then go Filter > Pixelate > Color Halftone. I chose the smallest dot, 4 pixels wide. The layer is set to Multiply at 10% Opacity – just enough to see it.
The image below of Kanye West was created by using the above techniques.