You ever get really close to your TV? Like, REALLY close? So close you could see the red, blue, and green squares that made up the image on your screen?
First start with whatever image you want. I started with this, courtesy of PhotoSpin.com
Now let's create the RGB pattern. Create a New File Ctrl + N. Set the Width to 6 pixels, Height to 1 pixel. Zoom in really close to about 800%. Ctrl + =. Select the Pencil tool. Click on your Color Picker boxes. To get a perfect red, set the Hex value to FF0000.
Use the Pencil Tool to draw a 2-pixel wide red rectangle on the left of your image.
Go back to the Color Picker and choose Green 00FF00. Draw 2 more pixels next to the red. Then choose Blue 0000FF and fill next to the green. You should get an image like this:
Press Ctrl + A to select your whole image. Go up to Edit>Define Pattern.... You can name your pattern whatever you want. Go back to your original image and create a new Adjustment Layer Pattern. When the dialog pops-up, select the pattern you just defined.
Set your Adjustment Layer mode to Overlay and adjust the Opacity to 55%. Select your bottom Layer in the Layer Palette and press Ctrl + J to duplicate that layer. Go up to Filter>Pixelate>Mosaic. Set the Cell Size to 4 or whatever you think looks right.
And that's about it. You can adjust the Opacity or Color Modes on your pattern Layer to get different effects.






More Photoshop: