Add this node in front of a Scale node to get a pixelated (non-smoothed) image from the resultant upscaled image.
Standard image input.
This node has no properties.
Standard image output.
Open an image you would like to pixelate using an Image node. Add two Scale nodes between the input and output. Change the values of X and Y to 0.2 in the first scale box and to 5 in the second. The composited image will appear unchanged. Now add a Pixelate node between the two Scale nodes. The result will be a pixelated image.