Image editing
Image editing encompasses the processes of altering images, whether they are digital photographs, traditional photo-chemical photographs, or illustrations. Traditional analog image editing is known as photo retouching, using tools such as an airbrush to modify photographs or edit illustrations with any traditional art medium. 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. The term "image editing" usually refers only to the editing of 2D images, not 3D ones.
Basics of image editing
images are stored on 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. This article mostly refers to bitmap graphics editors, which are often used to alter photographs and other raster graphics. However, vector graphics software, such as Adobe Illustrator, CorelDRAW, Xara Designer Pro or Inkscape, is used to create and modify vector images, which are stored as descriptions of lines, Bézier curves, 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. Vector images can be modified more easily because they contain descriptions of the shapes for easy rearrangement. They are also scalable, being rasterizable at any resolution.Automatic image enhancement
Camera or computer image editing programs often offer basic automatic image enhancement features that correct color hue and brightness imbalances as well as other image editing features, such as red eye removal, sharpness adjustments, zoom features and automatic cropping. These are called automatic because generally they happen without user interaction or are offered with one click of a button or mouse button or by selecting an option from a menu. Additionally, some automatic editing features offer a combination of editing actions with little or no user interaction.Software apps offering automatic enhancement of images or photos include Adobe, Fotor, Picsart, Radiant Photo, Skylum and Imagen.
Super-resolution imaging
Image editing that affects content
Listed below are some of the most used capabilities of the better graphics manipulation programs. The list is by no means all-inclusive. There are a myriad of choices associated with the application of most of these features.Selection
One of the prerequisites for many of the applications mentioned below is a method of selecting part of an image, thus applying a change selectively without affecting the entire picture. Most graphics programs have several means of accomplishing this, such as:- a marquee tool for selecting rectangular or other regular polygon-shaped regions,
- a lasso tool for freehand selection of a region,
- a magic wand tool that selects objects or regions in the image defined by proximity of color or luminance,
- vector-based pen tools,
Layers
Another feature common to many graphics applications is that of Layers, which are analogous to sheets of transparent acetate, stacked on top of each other, each capable of being individually positioned, altered, and blended with the layers below, without affecting any of the elements on the other layers. This is a fundamental workflow that has become the norm for the majority of programs on the market today, and enables maximum flexibility for the user while maintaining non-destructive editing principles and ease of use.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 selecting 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.Cutting out a part of an image from the background
Using a selection tool, the outline of the figure or element in the picture is traced/selected, and then the background is removed. Depending on how intricate the "edge" is this may be more or less difficult to do cleanly. For example, individual hairs can require a lot of work. Hence the use of the "green screen" technique which allows one to easily remove the background.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.Images can also be digitally altered in a commercial context, such as in fashion magazines and on billboards. Models can be made to look thinner, or have their wrinkles and eye bags digitally removed so they appear flawless.
Image editing that affects appearance
Change color depth
It is possible, using the software, to change the color depth of images. Common color depths are 2, 4, 16, 256, 65,536 and 16.7 million colors. The JPEG and PNG image formats are capable of storing 16.7 million colors. In addition, grayscale images of 8 bits or less can be created, usually via conversion and down-sampling from a full-color image. Grayscale conversion is useful for reducing the file size dramatically when the original photographic print was monochrome, but a color tint has been introduced due to aging effects.Contrast change and brightening
Image editors have provisions to simultaneously change the contrast of images and brighten or darken the image. Underexposed images can often be improved by using this feature. Recent advances have allowed more intelligent exposure correction whereby only pixels below a particular luminosity threshold are brightened, thereby brightening underexposed shadows without affecting the rest of the image.The exact transformation that is applied to each color channel can vary from editor to editor. GIMP applies the following formula:
if
value = value * ;
else
value = value + ;
value = * ) + 0.5;
where value is the input color value in the 0..1 range and brightness and contrast are in the −1..1 range.
Gamma correction
In addition to the capability of changing the images' brightness and/or contrast in a non-linear fashion, most current image editors provide an opportunity to manipulate the images' gamma value.Gamma correction is particularly useful for bringing details that would be hard to see on most computer monitors out of shadows. In some image editing software, this is called "curves", usually, a tool found in the color menu, and no reference to "gamma" is used anywhere in the program or the program documentation. Strictly speaking, the curves tool usually does more than simple gamma correction, since one can construct complex curves with multiple inflection points, but when no dedicated gamma correction tool is provided, it can achieve the same effect.
Color adjustments
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 with the white balance incorrectly set. Special effects, like sepia tone 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.The red-eye effect, which occurs when flash photos are taken when the pupil is too widely open, can also be eliminated at this stage.
Dynamic blending
Advanced Dynamic Blending is a concept introduced by photographer Elia Locardi in his blog Blame The Monkey to describe the photographic process of capturing multiple bracketed exposures of a land or cityscape over a specific span of time in a changing natural or artificial lighting environment. Once captured, the exposure brackets are manually blended together into a single High Dynamic Range image using post-processing software.Dynamic Blending images serve to display a consolidated moment. This means that while the final image may be a blend of a span of time, it visually appears to represent a single instant.