Seurat can do sharp edges too providing a great looking pixelization effect. Just set the shape object to 'rect' to override the default 'circ' option.
paper.seurat({ imageSource: 'imgs/fort-samson.png', shape: 'rect'});
Note paper is a Raphaël canvas object as defined here.
Chrome Users Because SeuratJS uses the HTML5 canvas element if you are attempting to debug from file:// as opposed to a local webserver you will need to run Chrome using the --allow-file-access-from-files flag. More info here.