ویدئو پروژکتور

از ویکی‌پدیا، دانشنامهٔ آزاد
(تغییرمسیر از پروژکتور)
پرش به ناوبری پرش به جستجو
فارسیEnglish
پروژکتور DLP InFocus IN34.

ویدئو پروژکتور (به انگلیسی: Video projector) یا ویدئو فراتاب دستگاهی است که برای نمایش تصاویر انفورماتیک روی یک پرده یا دیوار سفید استفاده می‌شود. با رشد سریع تکنولوژی در انتشار اطلاعات و ارتباطات در این ۱۰سال اخیر شرکت، مدارس، دانشگاه و دیگر ارگان‌ها برای سادگی در آموزش از این سیستم استفاده می‌کنند.

داستان ثبت اختراع[ویرایش]

فردی به نام «فرانسیس جنکینز» آنچه را که بعدها پروژکتور نام گرفت، یعنی دستگاهی که نوار مجموعه‌ای از عکسهای به هم چسبیده را با سرعت یک بیست و چهارم ثانیه نشان می‌دهد، اختراع کرد. اما حامی مالی وی این دستگاه را دزدید و آن را به شرکت بزرگی که صاحب سالن‌های تئاتر و سینما بود فروخت.

این شرکت آن را «ادیسون ویتاسکوپ» نامید فقط به این خاطر که در آن زمان اسم ادیسون مشهور بود و می‌توانست به موفقیت این دستگاه کمک کند. آنچه که بعدها از قبل اختراع این دستگاه به توماس ادیسون نسبت داده می‌شد در حقیقت نتیجه یک دزدی آشکار بود.[۱]

دسته‌بندی[ویرایش]

دیتا پروژکتورها اصولاً به دو دسته DLPو 3LCD تشکیل شده‌اند.

دیتا پروژکتورهای 3LCD تصاویر را واضح تر، پرنورتر و با غلظت رنگ بیشتر نمایش می‌دهند. هرچند این ویژگی باعث یک مشکل بزرگ به نام مشاهده شدن پیکسل‌ها می‌شود.

در مشخصه روشنایی ویدئو پروژکتور در سایت‌ها، فقط نور سفید دستگاه ذکر می‌شود و روشنایی نور رنگی ذکر نمی‌شود. باید توجه داست که نور سفید و رنگی در تکنولوژی 3LCD برابر عدد تعیین شده‌است ولی در تکنولوژی DLP، روشنایی نور سفید فقط ذکر می‌شود و روشنایی نور رنگی تقریباً ۱/۳ نور سفید است که اصلاً ذکر نمی‌شود. از این جهت تعداد رنگ‌ها در تکنولوژی 3LCD، سه برابر رنگ‌های با دستگاه‌های مبتنی بر تکنولوژی DLP می‌باشد.

در DLPها از یک چیپ برای تولید رنگ‌ها استفاده شده‌است. به همین دلیل از DLPها بیشتر برای مصارف سازمانی و آموزشی که کیفیت رنگ‌ها در اولویت قرار ندارد استفاده می‌شود.

DLPهای قدیمی تر یک مشکل بزرگ به اثر رنگین کمان دارند که در اثر قاطی شدن رنگ‌ها به وجود می‌آید.

مزایای دیتا پروژکتور DLP[ویرایش]

  • در DLPها پدیده Screen Door کمتر به چشم می‌خورد.
  • تصاویر صاف تری ارائه می‌دهند.
  • رنگ سفید را با عمق بالایی نمایش می‌دهند.
  • به دلیل استفاده از قطعات کمتر، عمر بیشتری نسبت به 3LCDها دارند.

مزایای دیتا پروژکتور 3LCD[ویرایش]

  • 3LCDها نور بیشتری نسبت به DLPها دارند. یعنی با وجود داشتن لامپ یکسان، تصویر روشن تری تولید می‌کنند.
  • غلظت رنگ بالایی و تصویر جذاب تری دارند. اگر یک 3LCD سه هزار لومنی را در کنار یک DLP سه هزار و ششصد لومنی قرار دهید و تصویری رنگی را در هر دو پروژکتور نمایش دهید، بیننده 3LCD را انتخاب خواهد کرد.

در مجموع DLPها برای مصارف تجاری و آموزشی و 3LCDها برای مصارف خانگی، بازی و فیلم مناسب تر هستند.

منابع[ویرایش]

Projected image from a video projector in a home cinema.

A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright ultra high pressure mercury lamp, LED or solid state blue or RGB laser to provide the illumination required to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. If a blue laser is used, a phosphor wheel is used to turn blue light into white light, which is also the case with white LEDs. (White LEDs do not use lasers.) A wheel is used in order to prolong the lifespan of the phosphor, as it is degraded by the heat generated by the laser diode.

Video projectors are used for many applications such as conference room presentations, classroom training, home cinema and concerts. In schools and other educational settings,[1] they are sometimes connected to an interactive whiteboard. In the late 20th century they became commonplace in home cinema. Although large LCD television screens became quite popular, video projectors are still common among many home theater enthusiasts.

Overview

A video projector, also known as a digital projector, may project onto a traditional reflective projection screen, or it may be built into a cabinet with a translucent rear-projection screen to form a single unified display device.

Common display resolutions include SVGA (800×600 pixels), XGA (1024×768 pixels), SXGA+ (1400x1050 pixels), 720p (1280×720 pixels), and 1080p (1920×1080 pixels), 4K UHD (3840x2160), as well as 16:10 aspect ratio resolutions including WXGA+ (1280x800 pixels) and WUXGA (1920x1200 pixels)

The cost of a projector is typically driven by its base technology, features, resolution, and light output. A projector with a higher light output (measured in lumens, “lm”) is required for a larger screen or for a room with a larger amount of ambient light.[2] For example, a light output of approximately 1500 to 2500 ANSI lumens is suitable for small screens viewed in rooms with low ambient light; approximately 2500 to 4000 lm is suitable for medium-sized screens with some ambient light; over 4000 lm is needed for very large screens or for use in rooms with no lighting control such as conference rooms. High brightness large-venue models are increasingly common in Boardrooms, Auditoriums and other high profile spaces, and models up to 30,000 lm are used in large staging applications such as concerts, keynote addresses and displays projected on buildings.

A few camcorders have a built-in projector suitable to make a small projection; a few more powerful "pico projectors" are pocket-sized, and many projectors are portable.

Projection technologies

A Zenith Electronics 1200 CRT Projector based home theater, ca. 2006.
  • LCD projector using LCD light gates. This is the simplest system, making it one of the most common and affordable for home theaters and business use. Common problems include a visible “screen door” or pixelation effect,, and the LCD panels deteriorating from heat & UV rays, leading to discolored spots or holes in the image, although recent advances have reduced the severity of these issues in some models.
  • DLP projector using Texas InstrumentsDLP technology. This uses one, two, or three microfabricated light valves called digital micromirror devices (DMDs). The single- and double-DMD versions use rotating color wheels in time with the mirror refreshes to modulate color. The most common problem with the single- or two-DMD varieties is a visible “rainbow” which some people perceive when moving their eyes. More recent projectors with higher speed (2x or 4x) and otherwise optimised color wheels have lessened this effect. 3-chip DLP projectors do not have this problem, as they display each primary color simultaneously, and offer higher light output and more accurate color reproduction, however the cost is significantly higher and thus 3-chip DLP technology is typically used in large venue, high brightness models, as well as Digital Cinema projectors.
  • LCoS projectors (liquid crystal on silicon). Such projectors often process light in the Fourier domain, which enables correction of optical aberrations using Zernike polynomials.[3] Some commercially available technologies include:
    • D-ILA JVC’s Direct-drive Image Light Amplifier based on LCoS technology.
    • SXRD Sony’s proprietary variant of LCoS technology.
  • LED projectors use one of the above-mentioned technologies for image creation, with a difference that they use an array of Light Emitting Diodes as the light source, negating the need for lamp replacement.
  • Hybrid LED and laser diode system developed by Casio. Uses a combination of Light Emitting Diodes and 445 nm laser diodes as the light source, while image is processed with DLP (DMD) chip.
  • Laser diode projectors have been developed by Microvision and Aaxa Technologies. Microvision projectors use Microvision's patented MEMS laser beam-steering technology, whereas Aaxa Technologies uses laser diodes + LCoS.
  • Laser projectors are now available from most projector manufacturers, including Barco, Canon, Christie Digital, Dell, Epson, Hitachi, NEC, Optoma, Panasonic, Sony, Viewsonic and many others. These units use a laser light source (instead of conventional lamps), and are used with most common projection technologies, including Single & 3-Chip DLP, LCD and LCoS. They offer numerous advantages, including eliminating the high cost and downtime of replacing lamps, variations in brightness and color that occur as lamps age and improved color fidelity. Typical laser light sources used in projectors are rated for 20,000 hours before the light output is reduced to 50%, whereas lamps lose brightness quickly and need to be replaced after as little as 1000-2000 hours.

Obsolete technologies

Do-it-yourself video projectors

Some hobbyists build a do-it-yourself (DIY) projector for low cost. They build their projectors from kits, sourced components, or from scratch, using a television set as a light source. Through the internet, they obtain plans to construct them[4] for domestic and classroom use.

See also

References

  1. ^ Charles Proctor (January 18, 2007). "Christmas is a time for taking -- from schools". Los Angeles Times. Retrieved 2010-11-26.
  2. ^ Richard Cadena (2006). Automated Lighting: The Art and Science of Moving Light in Theatre, Live Performance, Broadcast, and Entertainment. Focal Press. p. 344. ISBN 978-0-240-80703-4.
  3. ^ Kaczorowski, Andrzej; Gordon, George S.; Palani, Ananta; Czerniawski, Stanislaw; Wilkinson, Timothy D. (2015). "Optimization-Based Adaptive Optical Correction for Holographic Projectors". Journal of Display Technology. 11 (7): 596–603. doi:10.1109/JDT.2015.2418436.
  4. ^ Frank Völkel (November 13, 2004). "Supersize Your TV for $300: Build Your Own XGA Projector!". Tom's Hardware. Retrieved 2010-11-26.