Common Image Editing Terminology
Image (or graphics) editing jargon can be confusing, especially for those who are just learning how to edit digital photographs. There are countless image editing and manipulation software packages available, each with its own options and features. Adding to the confusion for novices, most programs tend to use different names for the basic functions used to edit images.
In this Webopedia Quick Reference article, we'll explain the common terms to help you learn the basics of editing digital images.
Image dimensions are the length and width of your image, measured in pixels. Some graphics programs will allow you to view and work with your image in the equivalent inches or centimeters. Depending on what you plan to use your image for, you may want to change the image size. For example, if you are using a high-resolution digital photograph, you may want to make the image smaller for publishing on your blog or website. You will have a couple choices: resize or resample.
The Difference Between Image Resize and Resample
When you resize or resample an image, you're basically specifying a new pixel dimension (length and width) for that image. The resize algorithm duplicates or deletes pixels. If you choose resample it will smooth out edges and fill in missing pixels with the appropriate color. Because of the difference between resize and resample, it is generally best to use resize on computer-generated graphics and resample on photo images containing more than 256 colors.
How to Manipulate Image Color Depth
In computer graphics, color depth is how you describe the range of colors that can be used in an image. The more colors used in an image, the more realistic it will look. Common values for color depth include the following: 256 colors; 16-bit, which is up to 65,000 colors; and 24-bit, which is 16,777,216 colors. Computer-generated graphics and clip art are best suited to a lower color depth, while photos and realistic images are best suited to 24 and 32-bit color depth. The more colors your image contains, the larger the file size.
Original image (24-bit) showing zoom area
(Zoomed 200x185 crop) 256 colors (8 bit)
Zoomed 200x185 crop) 16 colors (4 bit)
Using Predefined Image Effects
Many image editing programs come with predefined algorithms that enable you to add special effects to your images. Image effects are used as a way to change your image to add an artistic look, make textured patterns, or produce an enhanced real-world view.
There are some standard image effects that you can expect to find in a good program. Effects let you do things like change the edges of your image, adjust the noise level, add textures, change the gradient and fine-tune many other aspects of your image.
With most programs you can simply select the name of the image effect and the program will produce the image with the effect, so you can save the image. You can also choose "undo" if you don't like the change and select another one to try. Also, you may find your program offers an effects browser, which will open your image as a thumbnail in a browser window that allows you to quickly preview how each effect will look before performing the action.
Some graphics programs will offer a few predefined effects, others designed with effects in mind may offer hundreds of image effects to choose from. The following examples show several common image effects.
Artistic Effect: Neon Glow
Illumination Effects: Sunburst
Texture Effects: Tiles
Digital Photo Effects
With the popularity of digital photography, most image editing programs offer image effects specifically designed for use on digital photographs. These types of effects are used to remove problems that can appear in your original digital photograph such as various lens corrections (pincushion or fisheye) and red-eye removal tools. Re-eye removal is becoming more of a standard photo effect in graphics programs. Some options will simply auto-detect red-eye when you run the function and remove it, while others provide more advanced options by allowing you to place a circle over the red-eye area and adjust the red-eye removal tool to your own liking. Others will provide a selection of human and animal eyes that you can use to fill in the red-eye on your own image.
Recommended Reading: Webopedia's Digital Camera Guide.
Making Color Adjustments
Color adjustments are used to change the overall tone of your image and to remove unwanted colors from your image as well. Changes in color adjustment will usually affect an entire image -- even if you have selected only a small portion of the image to be adjusted, unless you are working with images that have a color depth of 24-bit or higher.
Color adjustments tools take other colors from the image into consideration when running the algorithm. For example if you add grey to a blue water scene, the grey will be influenced by the blue. Color balance can also be used to produce interesting image effects. By adding grey and yellow, for example, you can produce a more aged or newspaper aged look to your image.
One element of color adjustment that is available in many graphics programs is color balance. This function allows you to control the amount of red, green and blue in an image. Other standard color adjustments found in many image editing programs allow you to adjust the brightness, contrast and gamma in the image. These options are used to correct the brightness and contrast of an image. Adjusting the brightness and contrast highlights midtones and shadows to bring out detail in either light or dark areas. Gamma adjusts the brightness and contrast in unison.
The following examples show images processed with different color adjustment functions.
Red Color Balance
Removing Noise and Artifacts
In digital images noise and artifacts can often be a problem in images. Noise is used to describe the occurrence of color dots or specks where there should be none. For example, in a digital image of a pool of blue water, you may notice white, grey or other colored specks in the image where it should be blue. An artifact is used to describe any visible defect in the image. Jaggies are stair-like lines that appear where there should be smooth straight lines or curves and are considered artifacts.
Again, the preset options for artifact and noise removal will differ among graphics programs, but good programs will offer pre-defined options for small scratch removal, which is useful when dealing with scanned images, noise removal with edge preserving, salt and pepper removal (which removes extraneous black and white dots), and also softening which will blur some noise in photographs and give a softer tone to the image. Some programs will also have a JPEG artifact removal which helps remove artifacts introduced by the JPEG compression algorithm.
RECOMMENDED READING: Webopedia's "Graphics File Formats" discusses the most common types of graphics file formats including TIFF, JPEG, GIF, and PNG.
Control Cursors (Tools)
Graphics programs offer a set of tools that you can use to make changes and manipulate your images through cursor movement. The tools differ but allow you to color or fill in areas of your image with user-selected colors, crop out sections of an image, erase the background, or replace colors in an image. Here are some commonly used tools you should become familiar with in your graphics program.
Using the crop function allows you to drag a rectangular shape around an area in your image to cut off the sides to make it the proper size or to remove unwanted parts. Most graphics applications allow you to crop images with a clip feature.
The Painting tool changes the area of your image where you use the cursor to add paint strokes to the image. You can use this tool to fill in single pixels, add hard or soft lines, or select areas to fill in with a solid color or, some programs will allow you to paint with a texture rather than a single color.
A part of the Paint tool that that allows you to select a brush shape (square, circle, oval and so on) and also the the thickness in pixels you want to paint on your image with. As you move your cursor over the image it leaves a stroke of color.
The Dropper tool allows you to choose a foreground or background color from your image to work with. If you had a specific blue in your image that you wanted to use with the paint tool, for example, you would use the dropper and click on one of the blue pixels to change your foreground color.
Eraser tools allow you to erase areas within your image to leave behind transparency or a background color. There is also a Background Eraser which provides more control in removing a background to transparent.
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