Digital image editing
Categories: Digital photography
Digital imaging is closely associated with digital photography and is used extensively in the fields of science, medicine, and forensics.
Basics of image editing
Images are stored in the computer in the form of a grid of picture elements called 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.
Image editing programs
Because of the popularity of digital cameras, image editing programs are readily available. Minimal programs, that do such operations as rotating and cropping (image)s are often provided within the digital camera itself, others are returned to the user on a compact disc (CD) when images are processed at a discount store. The more powerful programs contain algorithms that perform a large variety of advanced image manipulations. Popular digital image editors include Paint Shop Pro and Adobe Photoshop. For more, including free programs, see: List of bitmap graphics editors
Digital data compression
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 in 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 are lossless, such as PNG, which means no image quality is lost when the file is saved. The JPEG compression algorithm uses a lossy format, but the algorithm takes advantage of "psycho visual modeling" to reduce detail. The greater the compression, the lesser the quality. The JPEG algorithm utilizes the way the brain and eyes work to make loss of detail less noticeable.
Image editor features
Listed below are some of the most used capabilities of the better image editors. The list is by no means all inclusive. There are a myriad of choices associated with the application of most of these features.
Image size change
Image editors can resize an image, making it 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 re-sampling 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.
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.
Histogram
Image editors have provisions to create an image histogram of the image being edited. The histogram displays the brightness value of each pixel in the image along a 0 -255 baseline. 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.
Noise removal
Image editors have an algorithm which can add or remove noise an image. JPEG artifacts can be removed; scratches can be removed and an image can be despeckeled. Noise tends to invade images when pictures are taken in low light settings. A new picture can be antiqued by adding uniform monochrome noise. A thorough discussion of camera noise can be found at:Explanation of noise
Selective color change
Image editors have the ability to selectively change the color of specific items in an image.
Image orientation
Image editors have algorithms to all the image to rotated in any direction and to any degree. Mirror image can be created and images can be flipped (turned upside down). Images that are out of line can be straightened and perspective can be adjusted.
Merging of images
Image editors have provisions for merging one or more individual images into a single image. The orientation and placement of each image can be controlled. The two images shown here were once individual studio portraits.
Special effects
Image editors usually have a list of special effects that can create unusual results. Images to 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.
Change color depth
Image editors have provisions to change the color depth of images. Common color depths are 2, 16, 256, and 16million. The JPEG and PNG image format will store 16 million colors. There are also algorithms for grayscale.
Lens correction
Image editors have provisions to correct images for various pincushion, fisheye, and barrel distortion. The corrections are subtle, but can improve the appearance of some images.
Contrast change and brightening
Image editors have provisions to change the contrast of images and brighten or darken the image. Many an underexposed image can be improved by using this feature.
Sharpening and softening images
Image editors have provisions to sharpen images, blur images, and to soften images. Portraits often appear more pleasing when softened. Red-eye, which occurs when flash photos are taken, can also be eliminated.
Color adjustments
Image editors have provisions to adjust the color of images in a variety of ways. The color balance can be improved, colors and be faded in and out, tones can be changes. Special effects, like sepia and grayscale can be added to an image.
Conclusion
Image editors provide the means for altering and improving images in an almost endless number of ways. They accept images in a large variety of image formats, and after changes are made they allow the changed image to be saved in any number of image formats, at almost any size, and in varying degrees of compression. Most serious digital camera users will find the facilities of an image editor indispensable.