Raster 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.[citation needed]
There is promising research on using deep convolutional networks to perform super-resolution.[1] In particular work has been demonstrated showing the transformation of a 20x microscope image of pollen grains into a 1500x scanning electron microscope image using it.[2] While this technique can increase the information content of an image, there is no guarantee that the upscaled features exist in the original image and deep convolutional upscalers should not be used in analytical applications with ambiguous inputs.[3][4] These methods can hallucinate image features, which can make them unsafe for medical use.[5]
Many image file formats use data compression to reduce file size and save storage space. Digital compression of images may take place in the camera, or can be done on the computer with the image editor. When images are stored in JPEG format, compression has already taken place. Both cameras and computer programs allow the user to set the level of compression.
Some compression algorithms, such as those used in PNG file format, are lossless, which means no information is lost when the file is saved. By contrast, the more popular JPEG file format uses a lossy compression algorithm (based on discrete cosine transform coding) by which the greater the compression, the more information is lost, ultimately reducing image quality or detail that can not be restored. JPEG uses knowledge of the way the human visual system perceives color to make this loss of detail less noticeable.
Image editor features
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(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,
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.
Layers
Leonardo da Vinci's Vitruvian Man overlaid with Goethe's Color Wheel using a screen layer in Adobe Photoshop. Screen layers can be helpful in graphic design and in creating multiple exposures in photography.Leonardo da Vinci's Vitruvian Man overlaid a soft light layer Moses Harris's Color Wheel and a soft light layer of Ignaz Schiffermüller's Color Wheel. Soft light layers have a darker, more translucent look than screen layers.
Another feature common to many graphics applications is that of Layers, which are analogous to sheets of transparent acetate (each containing separate elements that make up a combined picture), 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.
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.
Uncropped image from camera
Lily cropped from larger 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 (chroma key) which allows one to easily remove the background.
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.[6]
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.
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.
Notice the branch in the original image
The eye is drawn to the center of the globe.
Selective color change
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.
Selective color change
Image orientation
Image orientation (from left to right): original, 30° CCW rotation, and flipped.
Image editors are capable of altering an image to be rotated in any direction and to any degree. Mirror images can be created and images can be horizontally flipped or vertically flopped. A small rotation of several degrees is often enough to level the horizon, correct verticality (of a building, for example), or both. Rotated images usually require cropping afterwards, in order to remove the resulting gaps at the image edges.
Perspective control: original (left), perspective distortion removed (right).
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 that 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 control lens, which achieves a similar correction in-camera without loss of definition.
Lens correction
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.
Enhancing images
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.[7] Programs specialized for image enhancement are sometimes called image editors.
Sharpening and softening images
Graphics programs can be used to both sharpen and blur images in a number of ways, such as unsharp masking or deconvolution.[8] Portraits often appear more pleasing when selectively softened (particularly the skin and the background) to better make the subject stand out. [citation needed] This can be achieved with a camera by using a large aperture, or in the image editor by making a selection and then blurring it. Edge enhancement is an extremely common technique used to make images appear sharper, although purists frown on the result as appearing unnatural.
Image sharpening: original (top), image sharpened (bottom).
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.
Photomontage of 16 photos which have been digitally manipulated in Photoshop to give the impression that it is a real landscape
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. Clipping paths may be used to add silhouetted images to vector graphics or page layout files that retain vector data. Alpha compositing, allows for soft translucent edges when selecting images. There are a number of ways to silhouette an image with soft edges, including selecting the image or its background by sampling similar colors, selecting the edges by raster tracing, or converting a clipping path to a raster selection. Once the image is selected, it may be copied and pasted into another section of the same file, or into a separate file. The selection may also be saved in what is known as an alpha channel.
A popular way to create a composite image is to use transparent layers. The background image is used as the bottom layer, and the image with parts to be added are placed in a layer above that. Using an image layer mask, all but the parts to be merged is hidden from the layer, giving the impression that these parts have been added to the background layer. Performing a merge in this manner preserves all of the pixel data on both layers to more easily enable future changes in the new merged image.
Slicing of images
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.
An example of some special effects that can be added to a picture
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,[9] or combinations thereof.
A complex effect in the first image from the right
Using custom Curves settings[10] in Image editors such as Photoshop, one can mimic the "pseudo-solarisation" effect, better known in photographic circles as the Sabattier-effect.
A pseudo-solarised color image
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.
Image after stamp tool processed
Change color depth
An example of converting an image from color to grayscale
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 (equal to 256 luminance values per color channel). 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
An example of contrast correction. Left side of the image is untouched.
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:[11]
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
An example of color adjustment using raster graphics editor
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 (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.
Dynamic blending
Before and After example of Advanced Dynamic Blending Technique created by Elia Locardi
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.[12][13][14]
Printing
Control printed image by changing pixels-per-inch
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 200ppi will produce a printed image of 8 × 6inches. The same image with 400ppi will produce a printed image of 4 × 3inches. Change the resolution to 800ppi, and the same image now prints out at 2 × 1.5inches. 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.
Portable Network Graphics is a raster-graphics file format that supports lossless data compression. PNG was developed as an improved, non-patented replacement for Graphics Interchange Format (GIF)—unofficially, the initials PNG stood for the recursive acronym "PNG's not GIF".
Adobe Photoshop is a raster graphics editor developed and published by Adobe for Windows and macOS. It was created in 1987 by Thomas and John Knoll. It is the most used tool for professional digital art, especially in raster graphics editing, and its name has become genericised as a verb although Adobe disapproves of such use.
In computer graphics and digital photography, a raster graphic represents a two-dimensional picture as a rectangular matrix or grid of pixels, viewable via a computer display, paper, or other display medium. A raster image is technically characterized by the width and height of the image in pixels and by the number of bits per pixel. Raster images are stored in image files with varying dissemination, production, generation, and acquisition formats.
Vector graphics are a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector display and printing hardware, vector data models and file formats, as well as the software based on these data models. Vector graphics are an alternative to raster or bitmap graphics, with each having advantages and disadvantages in specific situations.
2D computer graphics is the computer-based generation of digital images—mostly from two-dimensional models and by techniques specific to them. It may refer to the branch of computer science that comprises such techniques or to the models themselves.
A raster graphics editor is a computer program that allows users to create and edit images interactively on the computer screen and save them in one of many raster graphics file formats such as JPEG, PNG, and GIF.
A vector graphic editor is a computer program that enables its users to create, compose and edit images with the use of mathematical and geometrical commands rather than individual pixels. This software is used in creating high-definition vector graphic images that can be scaled indefinitely without losing their quality. The output is saved in vector graphic formats, such as EPS, ODG, or SVG.
CodedColor is a bitmap graphics editor and image organizer for computers running the Microsoft Windows operating system and is published by 1STEIN.
Corel Photo-Paint is a raster graphics editor developed and marketed by Corel since 1992. Corel markets the software for Windows and Mac OS operating systems, previously having marketed versions for Linux. Its primary market competitor is Adobe Photoshop.
Digital illustration or computer illustration is the use of digital tools to produce images under the direct manipulation of the artist, usually through a pointing device such as a graphics tablet or, less commonly, a mouse. It is distinguished from computer-generated art, which is produced by a computer using mathematical models created by the artist. It is also distinct from digital manipulation of photographs, in that it is an original construction "from scratch". Photographic elements such as background or texture may be incorporated into such works, but they are not necessarily the primary basis.
A number of vector graphics editors exist for various platforms. Potential users of these editors will make a comparison of vector graphics editors based on factors such as the availability for the user's platform, the software license, the feature set, the merits of the user interface (UI) and the focus of the program. Some programs are more suitable for artistic work while others are better for technical drawings. Another important factor is the application's support of various vector and bitmap image formats for import and export.
An image file format is a file format for a digital image. There are many formats that can be used, such as JPEG, PNG, and GIF. Most formats up until 2022 were for storing 2D images, not 3D ones. The data stored in an image file format may be compressed or uncompressed. If the data is compressed, it may be done so using lossy compression or lossless compression. For graphic design applications, vector formats are often used. Some image file formats support transparency.
In computer graphics, image tracing, raster-to-vector conversion or raster vectorization is the conversion of raster graphics into vector graphics.
Layers are used in digital image editing to separate different elements of an image. A layer can be compared to a transparency on which imaging effects or images are applied and placed over or under an image. Today they are an integral feature of image editor.
Helicon Filter, also referred to as Helicon, Filter, or as HF, was a proprietary commercial and shareware photo editing software program for Microsoft Windows, similar to such programs as Adobe Photoshop and GIMP, developed and published by Helicon Soft Ltd. Unlike these other programs, Helicon Filter is designed primarily to edit and improve existing photos and not for graphics creation. Helicon Filter's interface also differs from other programs in that compact toolbars and menus containing editing tools are replaced with labeled "filter" tabs, each tab containing labeled edit options specific to a single aspect of the picture. Although some editors used to Photoshop-style programs may initially find this layout unfamiliar and unlike the standard toolbar layout, beginners and those who don't recognize the standard icons generally find this very helpful for getting through the editing process.
PhotoLine is a general purpose bitmap and vector graphics editor developed and published by Computerinsel GmbH for Windows, macOS, and Linux/Wine. It was originally created in 1995 by Gerhard Huber and Martin Huber. The program combines bitmap and vector graphics editing in one seamless working application unlike most graphics software which tend to focus on either bitmap or vector editing and output. PhotoLine is considered as a market competitor to Adobe Photoshop.
Fatpaint is a free, online (web-based) graphic design and desktop publishing software product and image editor. It includes integrated tools for creating page layout, painting, coloring and editing pictures and photos, drawing vector images, using dingbat vector clipart, writing rich text, creating ray traced 3D text logos and displaying graphics on products from Zazzle that can be purchased or sold. Fatpaint integrates desktop publishing features with brush painting, vector drawing and custom printed products in a single Flash application. It supports the use of a pressure-sensitive pen tablet and allows the user to add images by searching Wikimedia, Picasa, Flickr, Google, Yahoo, Bing, and Fatpaint's own collection of public domain images. The completed project can be saved on Fatpaint's server or locally. Fatpaint is affiliated with Zazzle, and owned by Mersica.
Paintbrush is a raster graphics editor for Mac OS X. It aims to replace MacPaint, an image editor for the classic Mac OS last released in 1988. It also is an alternative to Microsoft Paint. It has basic raster image editing capabilities and a simple interface designed for ease of use. It exports as PNG, JPG, BMP, GIF, and TIFF. The application also is often used for pixel art because of its grid option, and is not made for large scale images or GIMP or Photoshop-like editing on pictures or photographs.
SAI or Easy Paint Tool SAI (ペイントツールSAI) is a lightweight raster graphics editor and painting software for Microsoft Windows developed by Koji Komatsu and published by Systemax. The prototype of the software was "Full Color Paint Tool -Sai-" for X68000, produced in October 1996. Development of the software began on August 2, 2004, and the first alpha version was released on October 13, 2006. The first beta version was the released on December 21, 2007, and SAI's official release (1.0.0) was on February 25, 2008. It has been available on Microsoft Windows from XP to 11. It is available in Japanese, German, and English. A version 2 is currently in development.
Photopea is a web-based photo and graphics editor. It is used for image editing, making illustrations, web design or converting between different image formats. Photopea is advertising-supported software. It is compatible with all modern web browsers, including Opera, Edge, Chrome, and Firefox. The app is compatible with raster and vector graphics, such as Photoshop's PSD as well as JPEG, PNG, DNG, GIF, SVG, PDF and other image file formats. While browser-based, Photopea stores all files locally, and does not upload any data to a server.
↑ Johnson, Justin; Alahi, Alexandre; Fei-Fei, Li (2016-03-26). "Perceptual Losses for Real-Time Style Transfer and Super-Resolution". arXiv:1603.08155 [cs.CV].
"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
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