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PIXELS AND RESOLUTION Computers store colors as pixels. (A single spot on the screen.) Resolution tells how those pixels are displayed on the screen. For example, if a picture has a resolution of 800 x 600, it means it has 800 pixels across, and 600 pixels down the screen. Standard VGA is 640 x 480 (or 480,000 pixels on the screen). The more pixels onscreen or in an image, the greater the detail or resolution of the image. Some common screen resolutions are 640 x 480, 800 x 600, 1,024 X 768, 1,280 x 1,024, 1,600 X 1,200. The number of pixels is only one part of a digital image. Images also have color. Every monitor supports a certain number of colors that can be displayed at once. The more colors used, the more realistic the image will look. Color support is measured by the number of bits used to store the color information for each pixel. |
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COMMON COLOR RESOLUTIONS 4 bits per pixel = 16 colors = STANDARD VGA 8 bits per pixel = 256 colors = SUPER VGA 16 bits per pixel = 65,536 colors = HIGH RESOLUTION 24 bit depth = 16.7 million colors = TRUE COLOR How 24 bit color is stored: Red 8 bit 256 shades Blue 8 bit 256 shades Green 8 bit 256 shades 256 x 256 x 256 = 16.7 Million Colors Interesting Fact: If an image doubles in size, the resolution is cut in half. (Like blowing up a picture, it looks grainier). |
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BITMAP OR RASTER VERSUS VECTOR FILES 2 main types of computer images: Raster Files (AKA Bitmap) - Store information about each individual pixel (think photograph). Vector Files - Store drawing instruction, doesn't care about each pixel (think drawing or CAD). Common Raster files: .BMP (Microsoft Windows) Large Files! .DIB (IBM OS2) .GIF (Graphics Interchange Format, CompuServe & Internet MOST COMMON) .PCX (Paint - Windows) .TIF Compressed format, ideal for cross platform (Tagged Image Format) .JPG or .JPEG (Joint Photographic Experts Group & Internet MOST COMMON) Common Vector files: (You can resize them without loss of resolution) .CAD Programs - CAM Computer Aided Design .CDR Corel Draw .WPG (Word Perfect, Draw Perfect) .PIC (Lotus) |
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IMAGE DOWNLOADING ISSUES The amount of data that can be transmitted across a link in a certain period of time is termed bandwidth and is often measured in bits per second (bps), kilobits per second (Kbps), or magabits per second (Mbps). The higher the bandwidth, the more data can be transmitted quickly. Unfortunately, users accessing the Internet via a modem often have very limited bandwidth available. Some common speeds and the approximate time it takes to transmit 1MB of data are shown below: 14.4 Kbps - 10 minutes 28.8 Kbps - 5 minutes 56 Kbps - 2.5 minutes ISDN - Approximately 1 minute Cable modem - Varies from 5 - 30 seconds T1 - 5 seconds |
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