Depending on the application and intent, some photograph manipulations are considered an art form because it involves the creation of unique images and in some instances, signature expressions of art by photographic artists. Ansel Adams employed some of the more common manipulations using darkroom exposure techniques, burning (darkening) and dodging (lightening) a photograph. Other examples of photo manipulation include retouching photographs using ink or paint, airbrushing, double exposure, piecing photos or negatives together in the darkroom, scratching instant films, or through the use of software-based manipulation tools applied to digital images. Software applications have been developed for the manipulation of digital images, ranging from professional applications to very basic imaging software for casual users.