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Raster Scan
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems. The word '' raster'' comes from the Latin word '' rastrum'' (a rake), which is derived from '' radere'' (to scrape); see also rastrum, an instrument for drawing musical staff lines. The pattern left by the lines of a rake, when drawn straight, resembles the parallel lines of a raster: this line-by-line scanning is what creates a raster. It is a systematic process of covering the area progressively, one line at a time. Although often a great deal faster, it is similar in the most general sense to how one's gaze travels when one reads lines of text. The data to be drawn is stored in an area of memory called the Framebuffer. This memory area holds the values for each pixel on the screen. These values are retrieved from the refresh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Raster-scan Display
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems. The word '' raster'' comes from the Latin word ''rastrum'' (a rake), which is derived from '' radere'' (to scrape); see also rastrum, an instrument for drawing musical staff lines. The pattern left by the lines of a rake, when drawn straight, resembles the parallel lines of a raster: this line-by-line scanning is what creates a raster. It is a systematic process of covering the area progressively, one line at a time. Although often a great deal faster, it is similar in the most general sense to how one's gaze travels when one reads lines of text. The data to be drawn is stored in an area of memory called the Framebuffer. This memory area holds the values for each pixel on the screen. These values are retrieved from the refresh bu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertical Blanking Interval
In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next frame. It is present in analog television, VGA, DVI and other signals. In raster cathode ray tube displays, the blank level is usually supplied during this period to avoid painting the retrace line — see raster scan for details; signal sources such as television broadcasts do not supply image information during the blanking period. Digital displays usually will not display incoming data stream during the blanking interval even if present. The VBI was originally needed because of the inductive inertia of the magnetic coils which deflect the electron beam vertically in a CRT; the magnetic field, and hence the position being drawn, cannot change instantly. Additionally, the speed of older circuits was limited. For horizontal deflection, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Persistence Of Vision
Persistence of vision traditionally refers to the optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye. The illusion has also been described as "retinal persistence", "persistence of impressions", simply "persistence" and other variations. A very commonly given example of the phenomenon is the apparent fiery trail of a glowing coal or burning stick while it is whirled around in the dark. Many explanations of the illusion actually seem to describe either positive afterimages or motion blur. "Persistence of vision" can also be understood to mean the same as " flicker fusion," the effect that vision seems to persist continuously when the light that enters the eyes is interrupted with short and regular intervals. When the frequency is too high for the visual system to discern differences between moments, light and dark impressions fuse together into a continuous impressi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interlaced Video
Interlaced video (also known as interlaced scan) is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the phi phenomenon. This effectively doubles the time resolution (also called ''temporal resolution'') as compared to non-interlaced footage (for frame rates equal to field rates). Interlaced signals require a display that is natively capable of showing the individual fields in a sequential order. CRT displays and ALiS plasma displays are made for displaying interlaced signals. Interlaced scan refers to one of two common methods for "painting" a video image on an electronic display screen (the other being progressive scan) by scanning or displaying each line or row of pixels. This technique uses two fields to create a frame. One field contains all ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flicker (screen)
Flicker is a visible change in brightness between cycles displayed on video displays. It applies to the refresh interval on cathode ray tube (CRT) televisions and computer monitors, as well as plasma computer displays and televisions. Occurrence Flicker occurs on CRTs when they are driven at a low refresh rate, allowing the brightness to drop for time intervals sufficiently long to be noticed by a human eye – see persistence of vision and flicker fusion threshold. For most devices, the screen's phosphors quickly lose their excitation between sweeps of the electron gun, and the afterglow is unable to fill such gaps – see phosphor persistence. A refresh rate of 60 Hz on most screens will produce a visible "flickering" effect. Most people find that refresh rates of 70–90 Hz and above enable flicker-free viewing on CRTs. Use of refresh rates above 120 Hz is uncommon, as they provide little noticeable flicker reduction and limit available resolution. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphor Persistence
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictures (television set, computer monitor), radar targets, or other phenomena. A CRT on a television set is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term ''cathode ray'' was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons. In CRT television sets and computer monitors, the entire front area of the tube is scanned repeatedly and systematically in a fixed pattern called a raster. In color devices, an image is produced by controlling the intensity of each of three electron beams, one for each additive primary color (red, green, and b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frame Rate
Frame rate (expressed in or FPS) is the frequency (rate) at which consecutive images ( frames) are captured or displayed. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be called the , and be expressed in hertz. Frame rate in electronic camera specifications may refer to the maximal possible rate, where, in practice, other settings (such as exposure time) may reduce the frequency to a lower number. Human vision The temporal sensitivity and resolution of human vision varies depending on the type and characteristics of visual stimulus, and it differs between individuals. The human visual system can process 10 to 12 images per second and perceive them individually, while higher rates are perceived as motion. Modulated light (such as a computer display) is perceived as stable by the majority of participants in studies when the rate is higher than 50 Hz. This perception of modulated light as steady is kn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refresh Rate
The refresh rate (or "vertical refresh rate", "vertical scan rate", terminology originating with the cathode ray tubes) is the number of times per second that a raster-based display device displays a new image. This is independent from frame rate, which describes how many images are stored or generated every second by the device driving the display. On cathode ray tube (CRT) displays, higher refresh rates produce less flickering, thereby reducing eye strain. In other technologies such as liquid-crystal displays, the refresh rate affects only how often the image can potentially be updated. Non-raster displays may not have a characteristic refresh rate. Vector displays, for instance, do not trace the entire screen, only the actual lines comprising the displayed image, so refresh speed may differ by the size and complexity of the image data. For computer programs or telemetry, the term is sometimes applied to how frequently a datum is updated with a new external value from anoth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XFree86
XFree86 is an implementation of the X Window System. It was originally written for Unix-like operating systems on IBM PC compatibles and was available for many other operating systems and platforms. It is free and open source software under the XFree86 License version 1.1. It was developed by the XFree86 Project, Inc. The lead developer was David Dawes. The last released version was 4.8.0, released December 2008. The last XFree86 CVS commit was made on May 18, 2009; the project was confirmed dormant in December 2011. For most of the 1990s and early 2000s, the project was the source of most innovation in X and was the ''de facto'' steward of X development. Until early 2004, it was almost universal on Linux and the BSDs. In February 2004, with version 4.4.0, The XFree86 Project began distributing new code with a copyright license that the Free Software Foundation considered GPL incompatible. Most open source operating systems using XFree86 found this unacceptable and moved to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XFree86 Modeline
: ''A mode line may also refer to a line for the Emacs and Vim editors that provides information about the file and modes.'' A modeline is a configuration line in xorg.conf or the XFree86 configuration file (XF86Config) that provides information to the display server about a connected computer monitor or television and how to drive it at a specified display resolution. The Modeline is based on the Generalized Timing Formula or the Coordinated Video Timings standards produced by VESA. Modelines are now rarely used, but XFree86 and the Xorg Server still allow them to be set should the EDID information be inadequate. Syntax Each modeline has ten parameters, beginning with a label for the resolution being specified. The second parameter specifies the rate of the pixel clock in megahertz. Then follow four numbers that together specify the ''x''-resolution (width) and related parameters, and four numbers that specify the ''y''-resolution (height). * Modeline syntax: * Flags (op ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ringing (signal)
In electronics, signal processing, and video, ringing is oscillation of a signal, particularly in the step response (the response to a sudden change in input). Often ringing is undesirable, but not always, as in the case of resonant inductive coupling. It is also known as hunting. It is closely related to overshoot, often instigated as damping response following overshoot or undershoot, and thus the terms are at times conflated. It is also known as ripple, particularly in electricity or in frequency domain response. Electricity In electrical circuits, ringing is an unwanted oscillation of a voltage or current. It happens when an electrical pulse causes the parasitic capacitances and inductances in the circuit (i.e. those that are not part of the design, but just by-products of the materials used to construct the circuit) to resonate at their characteristic frequency.Johnson, H. and Graham, M. ''High-Speed Digital Design: A Handbook of Black Magic''. 1993. pp. 88–90 Ringin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fall Time
In electronics, fall time (pulse decay time) t_f is the time taken for the amplitude of a pulse to decrease (fall) from a specified value (usually 90% of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10% of the maximum value exclusive of overshoot or undershoot). Limits on undershoot and oscillation (also known as ringing and hunting) are sometimes additionally stated when specifying fall time limits. See also *Rise time *Transition time In electronics, when describing a voltage or current step function, rise time is the time taken by a signal to change from a specified low value to a specified high value. These values may be expressed as ratiosSee for example , and . or, equivalen ... References *{{FS1037C MS188 Transient response characteristics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
