Image editing encompasses the processes of altering images , whether they be digital photographs , traditional analog photographs , or illustrations . Before digital scanners and cameras became mainstream, traditional analog image editing was known as photo retouching , using tools such as an airbrush to modify photographs, or editing illustrations with any traditional art medium . However, since the advent of digital images, analog image editing has become largely obsolete. Graphic software programs, which can be broadly grouped into vector graphics editors , raster graphics editors , and 3d modelers , are the primary tools with which a user may manipulate, enhance, and transform images. Many image editing programs are also used to render or create computer art from scratch.
Basics Of Image Editing
Raster images are stored in a computer in the form of a grid of picture elements, or pixels . These pixels contain the image's color and brightness information. Image editors can change the pixels to enhance the image in many ways. The pixels can be changed as a group, or individually, by the sophisticated algorithms within the image editors. The domain of this article primarily refers to bitmap graphics editors, which are often used to alter photographs and other raster graphics. However, vector graphics software, such as Adobe Illustrator or Inkscape , are used to create and modify vector images, which are stored as descriptions of lines , Bézier splines , and text instead of pixels. It is easier to rasterize a vector image than to vectorize a raster image- how to go about vectorizing a raster image is the focus of much research in the field of computer vision . People like vector images because they are easy to modify, containing descriptions of the shapes in them for easy rearrangement, as well as scalable, being rasterizable at any resolution - to rasterize a vector image is simply to render it, while scaling a raster image up involves guessing at data that isn't there (see aliasing and other articles on information theory for more), and even scaling a raster image down involves guessing unless the scaling factor is an integer.
Image Size Alteration
Image editors can resize images in a process often called image scaling , making them larger, or smaller. High image resolution cameras can produce large images which are often reduced in size for Internet use. Image editor programs use a mathematical process called resampling to calculate new pixel values whose spacing is larger or smaller than the original pixel values. Images for Internet use are kept small, say 640 x 480 pixels which would equal 0.3 megapixels .
Cropping An Image
Digital editors are used to crop images . Cropping creates a new image by removing a desired rectangular portion from the image being cropped. The unwanted part of the image is discarded. Image cropping does not reduce the resolution of the area cropped. Best results are obtained when the original image has a high resolution. A primary reason for cropping is to improve the image composition in the new image.
Image editors may feature a number of algorithms which can add or remove noise in an image. JPEG artifacts can be removed; dust and scratches can be removed and an image can be despeckled. Noise tends to invade images when pictures are taken in low light settings. A new picture can be given an 'antiquated' effect by adding uniform monochrome noise.
Removal Of Unwanted Elements
Most image editors can be used to remove unwanted branches, etc, using a "clone" tool. Removing these distracting elements draws focus to the subject, improving overall composition.
Perspective Correction And Distortion
Some image editors allow the user to distort (or "transform") the shape of an image. While this might also be useful for special effects, it is the preferred method of correcting the typical perspective distortion which results from photographs being taken at an oblique angle to a rectilinear subject. Care is needed while performing this task, as the image is reprocessed using interpolation of adjacent pixels, which may reduce overall image definition . The effect mimics the use of a perspective correction lens , which achieves a similar correction in-camera without loss of definition.
Merging Of Images
Many graphics applications are capable of merging one or more individual images into a single file. The orientation and placement of each image can be controlled. The two images shown here were once individual studio portraits
Image editors usually have a list of special effects that can create unusual results. Images may be skewed and distorted in various ways. Scores of special effects can be applied to an image which include various forms of distortion, artistic effects, geometric and texture effects, and combinations thereof.
The color of images can be altered in a variety of ways. Colors can be faded in and out, and tones can be changed using curves or other tools. The color balance can be improved, which is important if the picture was shot indoors with daylight film, or shot on a camera that with an incorrectly adjusted white balance . Special effects, like sepia and grayscale can be added to an image. In addition, more complicated procedures such as the mixing of color channels are possible using more advanced graphics editors.
Sharpening And Softening Images
Graphics programs can be used to both sharpen and blur images in a number of ways. Portraits often appear more pleasing when softened (particularly the background, to make the subject stand out more — this is an example of shallow depth of field which can be achieved with a camera by using a large aperture , or artificially within software, by selecting the background portion of an image, and then blurring it). The red-eye effect , which occurs when flash photos are taken when the pupil is too widely open (thus reflecting back the colour of the blood-rich retina), can also be eliminated. Edge enhancement is an extremely common technique used to make images appear sharper, although many purists frown on the end result as less natural-looking.