Display Basics

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Display devices work by receiving the PC signal on video adapter (expansion board in expansion slot or on-board adapter) to display a particular graphic or character. The adapter converts and sends the data for display into instructions for display device and difference is in type of video adapter (digital or analog) and display (CRT or LCD). Few terms are explained

Pixel – A pixel, or pel or picture element is the smallest unit of picture that can be represented or controlled. Each pixel has its own address which corresponds to its coordinates. Pixels are arranged in a two-dimensional grid, and are often represented using dots or squares.

Resolution – The display resolution of a display device is the number of distinct pixel in each dimension that can be displayed and is simply the physical number of columns and rows of pixels creating the display or how many pixels across and down are used to draw the screen For example resolution of 1,024 × 768 means 1,024 pixels across and 768 pixels down display device would use 786,432 (1,024 × 768 = 786,432) pixels to draw the screen. Higher resolution means more pixels which yield a sharper image. The visual resolution of a video signal or display is the amount of detail that can be seen.

Color depth or bit depth or bits per pixel (bpp) is the number of bits used to represent the color of a single pixel. Higher color depth gives a broader range of distinct colors. As the number of bits increases, the number of possible colors becomes large.

Video memory – It is memory dedicated to hold the information necessary for a graphics card to drive a display device. Its size is dependent on resolution and color depth as, with resolution of 1024×768 and 24-bit color depth needs 24 bits of memory to store that one screen element, and 786,432 elements would require close to 2.25MB.

True color – It is a method of representing and storing graphical image information in an RGB color space such that a very large number of colors, shades, and hues can be displayed in an image, such as in high quality photographic images or complex graphics. Usually, true color is defined to mean at least 256 shades of red, green, and blue, for a total of at least 16,777,216 color variations.

Interlaced and Non-Interlaced – These are two different types of scanning systems which “paint” the picture on the screen. Television is usually interlaced, and computer signals are progressive or non-interlaced. Both formats are incompatible with each other. An interlaced picture is painted by first scanning half of the lines and then scanning the second set of lines. A progressive, or non-interlaced, picture is painted on the screen by scanning all of the horizontal lines of the picture in one pass from the top to the bottom.

Aspect ratio – It is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, if width is divided into x unit of equal length and the height is measured using this same length unit, the height will be measured to be y units. For example, image with an aspect ratio of 16:9 can be 16 inches wide and 9 inches high or 16 centimeters wide and 9 centimeters high or 8 yards wide and 4.5 yards high.

Viewing angle: It is applicable to LCD as their brightness and color of images shift if viewed from an angle rather than facing the screen directly. It becomes more critical as panel size increases.

Refresh rate: It is also called “vertical scan frequency ” or “vertical scan rate” and is the number of times in a second that display hardware redraws the screen. If an image refreshes too slowly, you may notice a flicker. It is given in draws per second, or Hertz. At least 70Hz of refresh rate to use. This becomes more important as the screen size gets larger.

Dot pitch – It is the shortest distance between two dots of the same color on the monitor given in mm. Lower the number, closer the pixels are, and, thus, the sharper the image. An average dot pitch is 0.28mm. Anything smaller than 0.28mm is considered great.

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