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Thread: Graphics and Multimedia FAQ
Oct 18, 2004, 10:16 #1
Graphics and Multimedia FAQGraphics & Multimedia FAQ
Q. What is the difference between .gif and .jpeg?
A. GIF is short for Graphics Interchange Format. GIF's advantages is that it is supported by practically all web browsers, can include transparent backgrounds, supports interlacing (providing a low-resolution preview of the graphic to the viewer while it downloads), and can be used as an image map (allowing the viewer to click on the graphic as they would a regular link to another site.) GIF's disadvantages are that it can only support 8-bit color (or a palette no greater than 256 colors). It may also handle dithering poorly, which is the result of pixels in a graphic that try to mix themselves up to emulate different colors. Photographs saved as GIFs can also lose their detail and a wide range of values.
JPEG is short for Joint Photographers Experts Group. JPEG is superior in rendering color and detail found in photographs or graphics using blends, gradients, and other tonal variations. It also provides for greater compression options (Low, Medium, High, and Maximum) allowing the the artist the perfect balance between quality and file size. The disadvantages of JPEG files are that they cannot be saved in index-color mode, meaning that many people who view the images with 8-color monitors may experience unusual dithering patterns. JPEG files also do not allow for transparent backgrounds, so you are stuck with either leaving the background of the image the same color as the background of your page, or having to settle for a border around your image.
Metallic images (gold, silver, copper, steel, bronze) are created using different types of gradients. Some of the gradients can be quite complex. For this reason, most metallic images should be exported or saved as JPEGs rather than GIFs. A JPEG is much better at displaying a wide range of tones, which is what a gradient is.
Use a GIF format if your graphic consists primarily of line art or flat colors without gradients. JPEG-converted graphics are best for photographs or images with fine tonal variations in colors, such as images with gradients or metallic images. Choosing the right file format is not only important for the quality, but for keeping your image's file size to a minimum.
Q. What is Dithering?
A. Dithering is the most common means of reducing the color range of images down to the 256 (or fewer) colors seen in 8-bit GIF images. Most images are dithered in a diffusion or randomized pattern to diminish the harsh transition from one color to another. But dithering also reduces the overall sharpness of an image, and it often introduces a noticeable grainy pattern in the image. This loss of image detail is especially apparent when full-color photos are dithered down to the 216-color browser-safe palette.
Q. What is Bit Depth?
A. Bit depth--also called pixel depth or color depth--measures how much color information is available to display or print each pixel in an image. Greater bit depth (more bits of information per pixel) means more available colors and more accurate color representation in the digital image. For example, a pixel with a bit depth of 1 has two possible values: black and white. A pixel with a bit depth of 8 has 28, or 256, possible values. And a pixel with a bit depth of 24 has 224, or roughly 16 million, possible values. Common values for bit depth range from 1 to 64 bits per pixel.
Q. What is the standard dpi (dots per inch) resolution for print?
A. minimum 150 dpi
Q. What is the standard ppi (pixels per inch) for web design?
A. 72 ppi
Q. What is the difference between vector and raster objects?
A. Raster objects are made up of pixels and are considered resolution dependent because they contain a fixed number of pixels that are used to create the image. They will lose quality if enlarged beyond the number of pixels needed in a particular use. Since there is a fixed and therefore a limited number of pixels, the image becomes fuzzy as it is enlarged. Raster images are the best choice for creating subtle gradations of shades and color, such as in a photograph or in a computer-generated painting.
Vector objects are made of lines and curves that are defined mathematically in the computer. A vector graphic is resolution-independent. They can be made larger or smaller without any loss of quality to the image. Vectors can be printed at any size, on any output device, at any resolution, without losing detail and without altering the resolution of the image.
Q. What is RGB?
A. A color model that consists of red, green, and blue; the primary colors that are mixed to display the color of pixels on a computer monitor. Every color of emitted light can be created by combining these three colors in varying levels. RGB is often used in color coding on web pages, particularly for GIF files.
Q. What is CMYK?
A. A color model that describes each color in terms of the quantity of each secondary color (cyan, magenta, yellow), and "key" (black) it contains. The CMYK system is used for printing. For mixing of pigments, it is better to use the secondary colors, since they mix subtractively instead of additively. The secondary colors of light are cyan, magenta and yellow, which correspond to the primary colors of pigment (blue, red and yellow). In addition, although black could be obtained by mixing these three in equal proportions, in four-color printing it always has its own ink. This gives the CMYK model. The K stands for "Key' or 'blacK,' so as not to cause confusion with the B in RGB.
Q. What is Lab Color?
A. In the Lab color model, L defines the lightness of the color, and a and b define the color along a red/green and blue/yellow axis, respectively. The Lab model comprises all colors in the visual spectrum and is device-independent. It is useful for converting colors between other color models -- for example, from an RGB model to a CMYK model. It also can preserve original color values from one color reproduction device to another.
Q. What is Indexed Color?
A. Indexed color is a term describing a graphic that contains 256-colors or less. All .gif images are made of indexed colors. The colors are stored in a palette, that is sometimes referred to as a color lookup table. The indexed image's palette contains only the colors that are needed for the image, so it takes up less space on the webpage.
Q. What is Multichannel Color?
A. Multichannel mode uses 256 levels of gray in each channel. Multichannel images are useful for specialized printing.
Q. What is Duotone?
A. Duotones are used to increase the tonal range of a grayscale image. Although a grayscale reproduction can display up to 256 levels of gray, a printing press can reproduce only about 50 levels of gray per ink. This means that a grayscale image printed with only black ink can look significantly coarser than the same image printed with two, three, or four inks, each individual ink reproducing up to 50 levels of gray.
Sometimes duotones are printed using a black ink and a gray ink--the black for shadows and the gray for midtones and highlights. More frequently, duotones are printed using a colored ink for the highlight color. This technique produces an image with a slight tint to it and significantly increases the image's dynamic range. Duotones are ideal for two-color print jobs with a spot color (such as a PANTONE Color) used for accent.
Stock Photography FAQ
Q. What is the difference between Rights Managed and Royalty Free in purchasing Stock Photography?
A. RIGHTS MANAGED IMAGES are "rented" for a specific purpose at a specific price. Once you negotiate a fee with the agency (or photographer) for the specific use you have in mind, any other use is subject to an additional fee.
ROYALTY FREE IMAGES are purchased outright, either as single images or on disc volumes in bulk, and can be used any way you want, with certain restrictions.
Note: Each stock agency has it's own set of guidelines for Rights Managed and Royalty Free image purchasing but this is the basic rule of thumb.
Q. What exactly is "streaming media"?
A. "Streaming media" refers to listening to or viewing digital media-mainly audio or video-on your computer in real-time as it comes across the Internet. In the past, you had to wait up to an hour to hear or see a few minutes of downloaded audio and video. But with streaming media you can view content and information instantly-on anything from an ordinary telephone line to a broadband connection or office LAN.
Q. What's the difference between "download-and-play" versus "real-time" streaming?
A. Experiencing Internet media via the download-and-play method means exactly that-your computer downloads a compressed media file, such as MP3, from the Internet to your hard drive. Once that file has downloaded completely, the media starts to play. With real-time streaming, on the other hand, the media is broadcast directly to your computer from a server and played back as the information is received from the server.
HTTP Streaming (download-and-play)
Also known as progressive streaming, this method takes a compressed media file and downloads it to your computer's hard drive before playback using any Web server such as Apache, Roxen, Microsoft Internet Information Server or Netscape.
Real Time Streaming
Real-time streaming is broadcast to your computer directly from a server and played back as the information is received from the server, without waiting for the file to download. Real-time servers include the RealSystem Server and QuickTime's Darwin streaming server.
Q. What do I need to begin streaming?
A. To stream media via the Internet you first need some "content," such as audio or video, images, text or animation. You'll need to convert it to digital format (e.g., .avi for video or .wav for audio) using a capture card. Next you must compress that media with an encoder so it can travel efficiently over the Internet. And lastly you need a server to send the media to a player upon request.
These definitions will be helpful as you learn more about streaming media:
This is a special piece of hardware, such as the Osprey 100, installed on a computer that can translate video and audio input from a video source, such as a camcorder, into digital format and write it to the hard disk in a number of formats, some of which can be compressed and streamed. A sound card-you probably already have one on your computer-is usually sufficient for converting the signal from an audio source (like a microphone or tape recorder) into a .wav file that can be compressed for streaming.
High-quality audio and video files can be very large. In order for the data to stream efficiently over the Internet to a range of targeted bandwidths, it must be compressed into small information packets. This compression is done with encoding software, often called an "encoder," such as RealSystem Producer.
Note: RealSystem Producer Plus includes a bandwidth simulator that lets you see what your audience sees at each specified connection rate.
"Server" can refer to both hardware and software. A server is a computer (hardware) that contains the files (sometimes called "content") to be delivered. This server also houses the technology (software) to deliver these files over a network such as the Internet.
A player is any software application-such as RealPlayer-that receives streaming (digital) media from a Web or intranet server, decodes it and plays it back on your computer.
Q. What kinds of files can be streamed?
A. The streaming server software determines the types of digital media-such as WAV or AVI files-it can stream. RealSystem Server can stream over 45 different data types, mainly different formats of video and audio:
RealVideo, AVI, QuickTime
RealAudio, WAV, AU, MPEG-1, MPEG-2, MP3
RealPix, RealText, GIF, PNG, JPEG, SMIL, Flash
Q. What do "broadband" and "narrowband" mean?
A. "Broadband" and "narrowband" are terms used to describe the type of connection you have to the Internet, based on your connection speed. Broadband usually refers to high-speed connections of 200Kbps or higher (such as DSL or cable-modem connections), and narrowband refers to connections of less than 200Kbps (e.g., a regular dial-up modem using your phone line).
Q. What are codecs?
A. Whenever you encode some content, you're utilizing a codec. "Codec" is an abbreviation for compression/decompression. A codec can be either a software application or a piece of hardware that processes media through complex algorithms, which compress the file for streaming and then decompress it for playback. Unlike other kinds of file-compression packages that require you to decompress a file before viewing or listening, codecs decompress the media on-the-fly, so your audience can view or listen to a file from its original compressed format. Your audience sees your content immediately with minimal loss of quality from the original.
Q. How can I make my streaming presentations more dynamic?
A. Using a technology called SMIL (Synchronized Multimedia Integration Language, a W3C standard for Web media) you can combine different media types-audio, video, text, still images, Flash, etc.-in the order you want them to appear, and place them where you want them to appear in your player. It's one thing to simply show a video on the Web, but much cooler when you can create a fully interactive presentation featuring multiple media types.Former Design Your Site Team Leader