Bokeh in photography refers to the aesthetic quality of the blurring and out-of-focus areas of an image. Bokeh has been defined as "the way the lens renders out-of-focus points of light". However, differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing or unpleasant to the eye. Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.