Image editing

Image editing encompasses the processes of altering

from scratch. The term "image editing" usually refers only to the editing of 2D images, not 3D ones.

Basics of image editing

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Software apps offering automatic enhancement of images or photos include Adobe, Fotor, Picsart, Radiant Photo, Skylum and Imagen.

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.

One of the prerequisites for many of the applications mentioned below is a method of selecting part(s) 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
  regions in the image defined by proximity of color or luminance
  ,
• vector-based pen tools,

as well as more advanced facilities such as edge detection, masking, alpha compositing, and color and channel-based extraction. The border of a selected area in an image is often animated with the marching ants effect to help the user to distinguish the selection border from the image background.

Another feature common to many graphics applications is that of

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.

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.

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 (chroma key) which allows one to easily remove the background.

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.

It is possible, using the software, to change the

Image editors have provisions to simultaneously change the

if (brightness < 0.0)  value = value * ( 1.0 + brightness);
                  else value = value + ((1 - value) * brightness);
value = (value - 0.5) * (tan ((contrast + 1) * PI/4) ) + 0.5;

where value is the input color value in the 0..1 range and brightness and contrast are in the −1..1 range.

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.

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

The red-eye effect, which occurs when flash photos are taken when the pupil is too widely open (so that light from the flash that passes into the eye through the pupil reflects off the fundus at the back of the eyeball), can also be eliminated at this stage.

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.^[8][9][10]

Image editors have provisions to create an image histogram of the image being edited. The histogram plots the number of pixels in the image (vertical axis) with a particular brightness value (horizontal axis). Algorithms in the digital editor allow the user to visually adjust the brightness value of each pixel and to dynamically display the results as adjustments are made. Improvements in picture brightness and contrast can thus be obtained.^[11]

Image editors may feature a number of algorithms which can add or remove noise in an image. Some JPEG artifacts can be removed; dust and scratches can be removed and an image can be de-speckled. Noise reduction merely estimates the state of the scene without the noise and is not a substitute for obtaining a "cleaner" image. Excessive noise reduction leads to a loss of detail, and its application is hence subject to a trade-off between the undesirability of the noise itself and that of the reduction artifacts.

Noise tends to invade images when pictures are taken in low light settings. A new picture can be given an 'antiqued' effect by adding uniform monochrome noise.

Some image editors have color swapping abilities to selectively change the color of specific items in an image, given that the selected items are within a specific color range.

Image editors are capable of altering an image to be rotated in any direction and to any degree.

Some image editors allow the user to

Photo manipulation packages have functions to correct images for various lens distortions, including pincushion, fisheye, and barrel distortions. The corrections are in most cases subtle, but can improve the appearance of some photographs.

In computer graphics, the enhancement of an image is the process of improving the quality of a digitally stored image by manipulating the image with software. It is quite easy, for example, to make an image lighter or darker, or to increase or decrease contrast. Advanced photo enhancement software also supports many filters for altering images in various ways.^[12] Programs specialized for image enhancement are sometimes called image editors.

Graphics programs can be used to both sharpen and blur images in a number of ways, such as

Another form of image sharpening involves a form of contrast. This is done by finding the average color of the pixels around each pixel in a specified radius, and then contrasting that pixel from that average color. This effect makes the image seem clearer, seemingly adding details. An example of this effect can be seen to the right. It is widely used in the printing and photographic industries for increasing the local contrasts and sharpening the 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.

When selecting a raster image that is not rectangular, it requires separating the edges from the background, also known as silhouetting. This is the digital-analog of cutting out the image from a physical picture.

A popular way to create a composite image is to use transparent

A more recent tool in digital image editing software is the image slicer. Parts of images for graphical user interfaces or web pages are easily sliced, labeled and saved separately from whole images so the parts can be handled individually by the display medium. This is useful to allow dynamic swapping via interactivity or animating parts of an image in the final presentation.

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 transforms and texture effects,

pseudo-solarisation" effect, better known in photographic circles as the Sabattier-effect.

Stamp Clone Tool

The Clone Stamp tool selects and samples an area of your picture and then uses these pixels to paint over any marks. The Clone Stamp tool acts like a brush so you can change the size, allowing cloning from just one pixel wide to hundreds. You can change the opacity to produce a subtle clone effect. Also, there is a choice between Clone align or Clone non-align the sample area. In Photoshop this tool is called Clone Stamp, but it may also be called a Rubber Stamp tool.

Printing

Controlling the print size and quality of digital images requires an understanding of the pixels-per-inch (ppi) variable that is stored in the image file and sometimes used to control the size of the printed image. Within Adobe Photoshop's Image Size dialog, the image editor allows the user to manipulate both pixel dimensions and the size of the image on the printed document. These parameters work together to produce a printed image of the desired size and quality. Pixels per inch of the image, pixel per inch of the computer monitor, and dots per inch on the printed document are related, but in use are very different. The Image Size dialog can be used as an image calculator of sorts. For example, a 1600 × 1200 image with a resolution of 200 ppi will produce a printed image of 8 × 6 inches. The same image with 400 ppi will produce a printed image of 4 × 3 inches. Change the resolution to 800 ppi, and the same image now prints out at 2 × 1.5 inches. All three printed images contain the same data (1600 × 1200 pixels), but the pixels are closer together on the smaller prints, so the smaller images will potentially look sharp when the larger ones do not. The quality of the image will also depend on the capability of the printer.

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This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (March 2011) (Learn how and when to remove this message)

• "Fantasy, fairy tale and myth collide in images: By digitally altering photos of landscapes, artist Anthony Goicolea creates an intriguing world", The Vancouver Sun (British Columbia); June 19, 2006.
• "It's hard to tell where pixels end and reality begins", The San Francisco Chronicle; September 26, 2006.
• "Virtual Art: From Illusion to Immersion", MIT Press 2002; Cambridge, Massachusetts

External links

Wikimedia Commons has media related to Image editing.