Cropping refers to the removal of the outer parts of an image to improve framing, accentuate subject matter or change aspect ratio. Depending on the application, this may be performed on a physical photograph, artwork or film footage, or achieved digitally using image editing software. The term is common to the film, broadcasting, photographic, graphic design and printing industries.
In the printing, graphic design and photography industries, cropping refers to removing unwanted areas from a photographic or illustrated image. One of the most basic photo manipulation processes, it is performed in order to remove an unwanted subject or irrelevant detail from a photo, change its aspect ratio, or to improve the overall composition. In telephoto photography, most commonly in bird photography, an image is cropped to magnify the primary subject and further reduce the angle of view when a lens of sufficient focal length to achieve the desired magnification directly is not available. It is considered one of the few editing actions permissible in modern photojournalism along with tonal balance, colour correction and sharpening. A crop made from the top and bottom of a photograph may produce an aspect which mimics the panoramic format (in photography) and the widescreen format in cinematography and broadcasting. Both of these formats are not cropped as such, rather the product of highly specialised optical configuration and camera design.
Cropping in order to emphasize the subject:
Cropping in order to remove unwanted details/objects:
In certain circumstances, film footage may be cropped to change it from one aspect ratio to another, without stretching the image or filling the blank spaces with letterbox bars (fig. 2).
Aspect ratio concerns are a major issue in film making. Rather than cropping, the cinematographer traditionally uses mattes to increase the latitude for alternative aspect ratios in projection and broadcast. Anamorphic optics (such as Panavision lenses) produce a full-frame, horizontally compressed image from which broadcasters and projectionists can matte a number of alternative aspect ratios without cropping relevant image detail. Without this, widescreen reproduction, especially for television broadcasting, is dependent upon a variety of soft matting techniques such as letterboxing, which involves varying degrees of image cropping (see figures 2, 3 and 4)
Since the advent of widescreen television, a similar process removes large chunks from the top & bottom to make a standard 4:3 image fit a 16:9 one, losing 25% of the original image. This process has become standard in the United Kingdom, in TV shows where many archive clips are used, which gives them a zoomed-in, cramped image with significantly reduced resolution. Another option is a process called pillarboxing, where black bands are placed down the sides of the screen, allowing the original image to be shown full-frame within the wider aspect ratio (fig. 6). See this article for a fuller description of the problem.Typical cropping in cinematographic and broadcast applications
Various methods may be used following cropping or may be used on the original image.Vignetting is the accentuation of the central portion of an image by blurring, darkening, lightening, or desaturation of peripheral portions of the image
The use of non-rectangular mat or picture frame may be used for selection of portions of a larger image
It is not possible to "uncrop" a cropped image unless the original still exists or undo information exists: if an image is cropped and saved (without undo information), it cannot be recovered without the original.
However, using texture synthesis, it is possible to artificially add a band around an image, synthetically "uncropping" it. This is effective if the band smoothly blends with the existing image, which is relatively easy if the edge of the image has low detail or is a chaotic natural pattern such as sky or grass, but does not work if discernible objects are cut off at the boundary, such as half a car. An uncrop plug-in exists for the GIMP image editor.