Multi-Media Graphics Terms
Table of Contents
COLOURS
RGB - Primary Additive Colors - CMYK - Primary Subtractive Colors - Hue - Saturation - Luminance - HSL (Hue/Saturation/Lightness) - Opacity - Palette - Color Palette - Palette Transparency - Paletted Image - Threshold level - Dithering - Dithering Methods - Reduced Color Bleeding Option -
DISPLAY METHODS
Raster File Formats - Vector File Formats - Types of Resolution - Image Resolution - Monitor Resolution - Printer Resolution - Optical Resolution (scanner) - 1-bit image - 1-bit image - 1-bit image - 1-bit image - 1-bit image - True Color -
RECORDING GRAPHICS
Compression - Lossless Compression - Lossy Compression - Decompression - RLE (Run Length Encoding) - Interlacing - Crop - Monitors and Gamma - Pixel - PNG - Progressive Encoding - QuickTime - Thumbnails - Antialias - AVI - BMP - Alpha Channel - Channel - Digital Camera - FPS - Frame - Key Frame - GIF - JPEG - Unix Formats - TIFF - TWAIN -
Stands for Red/Green/Blue.
Red, green, and blue. When these three colors are combined, they produce white.
Stands for Cyan/Magenta/Yellow/Black. The four standard ink colors used in printing. Because of impurities in inks, cyan, magenta, and yellow produce a muddy brown when combined. Black (K) is often added.
Cyan, magenta, and yellow. When these three colors are combined, they produce black.
The shade or tint of a color. Also, one of the three components of the HSL color definition mode.
The purity of a hue or the amount of grey it contains. A hue with a saturation of 100% is vivid; a hue with a saturation of 0% is grey. Also, one of the three components of the HSL mode.
The lightness of a color, independent of its hue or saturation. The luminance of an image is displayed in the Histogram. A color with a luminance of 100% is white; a color with a luminance of 0% is black.
The density of a color or layer. A color or layer with an opacity of 0 is transparent; a color or layer with an opacity of 100 is complete opaque (solid).
As in a painter's palette, different palettes offer you the ability to select and mix colors, organize the different layers of paint on the canvas and pick a customized brush for a specific task.
Contains the selection of available colors and displays the active foreground and background colors.
Specific color in the palette that is assigned a transparent value. This is useful when working with some files formats, such as GIF and PNG.
An image with at most 256 colors.
The lightness value above which colors are inverted in Adjustment layers, the Glowing Edges effect and the Solarize command. All colors with lightness values above the set level are turned into their inverse (on the 255 scale). At a Threshold level of 1, all colors except black change. As the Threshold level increases, colors must be increasingly lighter to invert themselves.
A process that mixes monochrome with colored pixels or pixels of two or more colors to display colors that are not available. The process produces shading and highlighting that appear to the eye as different colors.
Dithering is a technique for simulating colors that are missing from an image file's palette. The missing colors are simulated by intermingling pixels of two or more palette colors. If the unavailable color differs too greatly from the colors in the image's palette, dithering produces a grainy or mottled appearance.
Error diffusion dithering is a popular dithering method. The "error" in the title refers to the cumulative difference between the actual values of pixels in the image and their "true" values if they were all set to their correct colors. By reducing this error, error diffusion dithering produces image quality that is superior to that achieved by non-error adjusted dithering.
The process starts at the first pixel in the image (the upper left corner). The algorithm finds the color in the palette that is nearest to the color of the pixel. It then compares the two colors' numerical values, saves the difference as the initial error, and applies the color from the palette to the pixel.
The process then proceeds to the second pixel. It finds this pixel's nearest color and calculates the sum of the color and the error value from the last pixel. It sets the pixel to the color that is nearest to this sum. Any difference between the applied color and the sum becomes the new error value.
When the process reaches the third pixel, it repeats the procedure that was used to set the color for the second pixel. The algorithm cycles through the image's remaining pixels in the same manner. The error value is abandoned at the end of each row.
The Reduce Color Bleeding Option
Error diffusion dithering causes colors to bleed from left to right because the algorithm, and therefore the error value, travels in this direction. Color bleed is most noticeable in images with hard vertical edges because the edges are softened by the traveling color.
Paint Shop Pro functions that use error diffusion dithering include a Reduce Color Bleeding option. This option lessens the left-to-right color bleed by applying a fractional coefficient to the error value. By reducing the error value, less color information is carried from one pixel to the next.
DISPLAY METHODS
A Raster image is composed of units of light, called pixels, which are laid out on a grid. If you increase the magnification of an image, you can see these pixels. They appear as squares in the screen. A Raster program creates objects by grouping pixels. An object is stored as a group of pixels with information about each pixel color. Pixels can be blended to create soft edges and smooth transitions between objects. This makes the format a good choice to use for saving photographs.
An image in the Raster format is resolution-dependent. You specify the resolution and pixel dimensions when you create the image. If you later decide to increase its size, you enlarge each pixel, which lowers the image quality.
A Vector image is composed of mathematical instructions for drawing the image. Each object in a Vector image is stored as a separate item with information about its relative position in the image, its starting and ending points, width, color, and curve information. This makes them suitable for logos, fonts, and line drawings.
An image in the Vector format is resolution-independent. It can be resized without losing detail because it is stored as a set of instructions, not a collection of pixels. Each time you display an image, you recreate it.
Note that a computer monitor uses pixels to display an image, and most printers convert pixels to ink dots. Vector images are rasterized (created using pixels) when displayed on the screen or printed. When you close them, they are saved in the Vector format.
When you work with computer graphics, you need to be aware of the resolution of the image, the monitor, and the printer.
An image is composed of small squares known as pixels. An image with smaller pixels means it contains more of them, and it therefore has a higher resolution, displays more detail, and is a larger file size than an image with bigger pixels. Image resolution is the number of pixels per unit of length of an image, and it is usually measured in pixels per inch (ppi).
Monitor resolution, which is the number of pixels per unit of length on a monitor, is usually measured in dots per inch (dpi). The resolution of PC monitors is approximately 96 dpi.
The printer resolution is the number of ink dots per inch a laser or imagesetter printer produces. Most laser printers have a resolution of about 300 to 600 dpi. You will generally get good results with images from 96 to 150 ppi.
When working with commercial printers, you may also hear the term screen frequency. This is the resolution, measured in lines per inch (lpi), of the halftone screens used to reproduce the images. When you are scanning color or greyscale images intended for commercial printing, the general rule is to scan them at 1.5 to 2 times the screen frequency of the printing device.
The actual number of pixels per inch at which a scanner is capable of capturing an image.
An image containing a maximum of 2 colors. These are black and white.
An image containing a maximum of 16 colors.
An image containing a maximum of 256 colors.
An image containing a maximum of 65,536 colors.
An image containing a maximum of 16,777,216 colors.
The common name for 24-bit color. "
True" is used because the human eye can distinguish among approximately six million different colors, which is fewer than the number of colors available in a 24-bit color system. 24-bit images use 8 bits for each RGB channel. With 32-bit color depth, another 8 bits are used for an Alpha Channel.
RECORDING GRAPHICS
The process by which some of an image's data is either stored in patterns or eliminated in order to reduce file size.
Compression method that retains all of the original image data and reduces the file size by storing patterns of pixels in the image.
Compression method that eliminates data to reduce the file size.
To reverse the compression software algorithm to return data to its original size and condition. For files compressed with lossy compression, some data will not be restored.
A method for reducing file size by compressing repetitive information. It discards continuous regions of duplicate color to compress most multi-layered image to about 75% of their original sizes.
Interlacing places a rough, blurry copy of the image at the beginning of the data stream, which allows people viewing the image on the Internet to see that copy first. The file gradually sharpens as the image loads.
To remove part of an image outside a specified boundary.
An image is stored in computer memory as a series of numbers. Depending on the image's format, a pixel's values can be described in a variety of ways. All these formats have at least one thing in common: a higher number means a brighter color value. This rule has two corollaries: (1) the highest combination of values possible for a pixel produces pure white; and (2) the lowest combination of values possible for a pixel produces pure black.
It would follow logically that a value half way up any scale would have a lightness exactly between black and white. This assumes that the hypothetical scale would allow an integer value exactly in the middle. In reality, it would not. Image formats are based on powers of two, so integer midpoints are not possible.
To get over this hurdle, consider an approximate midpoint, and to base it in reality, assume that the image is in a grey scale format. A graph of a monitor's pixel output over the image's potential pixel values would look like the following diagram, "Linear Brightness." The approximate midpoint -- say 120 -- would produce an identical brightness on the monitor.
Linear Brightness
A computer monitor displays colors by exciting phosphors on the screen. Unfortunately, phosphors do not excite linearly. For example, if a computer reads a lightness value from a photographic image and sends it directly to the monitor, the displayed color is dimmer than in the original photograph.
This is where gamma correction comes in. A gamma correction value adjusts for the non-linearity of phosphor excitation. The diagram below displays an example of how gamma correction can alter the color values sent to a computer monitor. In this case, the approximate midpoint of 120 produces a monitor value of 168.
Gamma Corrected Brightness
Stands for picture element. One of the individual squares that make up a raster image and the smallest element that can be assigned a color. If you zoom in on an image, you can see the individual pixels.
Stands for Portable Network Graphics. A file format designed for web graphics. It supports 24-bit color with lossless compression, one alpha channel, and alpha transparency.
Progressive encoding allows viewers of the image to see a rough, blurry copy of the image as it downloads. The file gradually sharpens as the image loads.
Apple Computer's video environment. QuickTime video files must be converted to AVI format to run under Microsoft's Video for Windows, however Apple provides a QuickTime viewer for Windows. INDEO video is supported under Apple's Macintosh operating system.
A thumbnail is a small preview of an image that lets you identify and manage it without opening the actual image.
The blending of the pixel colors along the edges to eliminate the stair-stepping look (called "jaggies") of curved and slanted lines. This feature is commonly used with text.
Stands for Audio Video Interlaced. The file format for Microsoft Windows digital video and audio. This format is cross platform compatible, allowing AVI video files to be played on other computer platforms.
Stands for Bitmap. A standard Microsoft Windows image format. Supports paletted, 24-bit RGB color, and greyscale images. This format does not support alpha channels, layers or vector data.
An image composed of an array of small squares, called pixels, arranged in rows and columns. Each pixel has a specific color value and location.
A greyscale channel for storing selections and masks in an image.
Contains all of the pixel information for a single color. A greyscale image has one channel, an RGB image has three channels, and a CMYK image has four channels.
A camera that takes pictures with a CCD (charge-coupled device) and stores them in a memory module or on removable media. The pictures can usually be transmitted to a computer.
Stands for Frames Per Second. This is the rate at which animations are displayed.
A single, complete image in a connected series of images such as an Animation Shop animation, a video recording, or a film recording.
A baseline frame against which other frames are compared for differences. If the clip has a large amount of motion, better playback will occur with every frame being a Key Frame. If there is very little motion, such as a narrator, a higher number of Delta Frames (intervening frames that are compressed based on differences from the key frames) will give satisfactory playback. In general making every 3rd frame a Key frame is a good choice with the current Indeo algorithm.
Stands for Graphic Interchange Format. This is a file format commonly used on the Internet. It uses lossless compression and creates images in 8-bit color. GIF supports single-color transparency and animation. GIF does not support layers or alpha channels.
HSL (Hue/Saturation/Lightness)
A method for defining colors in an image.
Stands for Joint Photographics Experts Group. A compression technique that supports 24-bit images and can reduce a file's size by as much as 96%. It removes some color information, while retaining the brightness data. At higher compressions it can result in a visible loss of quality. It is best for photographs and for images that contain a variety of tonal values. JPG has been adapted to video, but it provides no frame compression.
PPM (Portable Pixelmap), PGM (Portable Graymap), and PBM (Portable Bitmap) are UNIX native formats for exchanging images in color and grayscale respectively.
(Paint Shop Pro), is the native image format for Paint Shop Pro. It can contain layer, vector, mask, and selection information for images. The PSP format provides optional lossless compression to create smaller files.
Stands for Tagged Image File Format. A file format used for scanning, storing, and interchanging color and greyscale images. It does not support layers or animation.
An industry-wide compatibility standard for devices such as scanners and digital cameras to communicate with applications like Paint Shop Pro, allowing you to import an image into Paint Shop Pro without leaving the program