WHX112減速機殼加工工藝及夾具設(shè)計(論文+DWG圖紙)
WHX112減速機殼加工工藝及夾具設(shè)計(論文+DWG圖紙),whx112,減速,機殼,加工,工藝,夾具,設(shè)計,論文,dwg,圖紙
攀枝花學院畢業(yè)設(shè)計(論文)
外文資料及譯文
原文：
Television Video Signals
Although over 50 years old , the standard television signal is still one of the most common way to transmit an image. Figure 8.3 shows how the television signal appears on an oscilloscope. This is called composite video, meaning that there are vertical and horizontal synchronization (sync) pulses mixed with the actual picture information.
These pulses are used in the television receiver to synchronize the vertical and horizontal deflection circuits to match the video being displayed. Each second of standard video contains 30 complete images, commonly called frames , A video engineer would say that each frame contains 525 lines, the television jargon for what programmers call rows. This number is a little deceptive because only 480 to 486 of these lines contain video information; the remaining 39to 45 lines are reserved for sync pulses to keep the television’s circuits synchronized with the video signal.
Standard television uses an interlaced format to reduce flicker in the displayed image. This means that all the odd lines of each frame are transmitted first, followed by the even lines. The group of odd lines is called the odd field, and the group of even lines is called the even field. Since each frame consists of two fields, the video signal transmits 60 fields per second. Each field starts with a complex series of vertical sync pulses lasting 1.3 milliseconds. This is followed by either the even or odd lines of video. Each line lasts for 63.5 microseconds, including a 10.2 microsecond horizontal sync pulse, separating one line from the next. Within each line, the analog voltage corresponds to the gray scale of the image, with brighter values being in the direction away from the sync pulses. This place the sync beyond the black range. In video jargon, the sync pulses are said to be blacker than black..
The hardware used for analog-to-digital conversion of video signals is called a frame grabber. This is usually in the form of an electronics card that plugs into a computer, and connects to a camera through a coaxial cable. Upon command from software, the frame grabber waits for the beginning of the next frame, as indicated by the vertical sync pulses. During the following two fields,each line of video is sampled many times, typically 512,640 or 720 samples per line, at 8bits per sample. These samples are stored in memory as one row of the digital image.
This way of acquiring a digital image results in an important difference between the vertical and horizontal directions. Each row in the digital image corresponds to one line in the video signal, and therefore to one row of wells in the CCD. Unfortunately, the columns are not so straightforward. In the CCD, each row contains between about 400 and 800 wells (columns), depending on the particular device used. When a row of wells is read from the CCD, the resulting line of video is filtered into a smooth analog signal, such as in Figure 8.3. In other words, the video signal does not depend on how many columns are present in the CCD. The resolution in the horizontal direction is limited by how rapidly the analog signal is allowed to change. This is usually set at 3.2 MHz for color television, resulting in a rise time of about 100 nanoseconds, i.e, about 1/500th of the 53.2 microsecond video line.
When the video signal is digitized in the frame grabber, it is converted back into columns, However, these columns in the digitized image have no relation to the columns in the CCD. The number of columns in the digital image depends solely on how many times the frame grabber samples each line of video. For example, a CCD might have 800 wells per row, while the digitized image might only have 512 pixels (i.e , columns) per row.
The number of columns in the digitized image is also important for another reason. The standard television image has an aspect ratio of 4 to 3, i.e. , it is slightly wider than it is high. Motion pictures have the wider aspect ratio of 25 to 9. CCDs used for scientific applications often have an aspect ratio of 1 to 1, i.e , a perfect square. In any event, the aspect ratio of a CCD is fixed by the placement of the electrodes, and cannot be altered. However, the aspect ratio of the digitized image depends on the number of samples per line. This becomes a problem when the image is displayed, either on a video monitor or in a hardcopy. If the aspect ratio isn’t properly reproduced, the image looks squashed horizontally or vertically.
The 525 line video signal described here is called NTSC (National Television Systems Committee), a standard defined way back in 1954. This is the system used in the United States and Japan. In Europe there are two similar standards called PAL (Phase Alternation by Line) and SECAM (Sequential Chrominance And Memory). The basic concepts are the same , just the numbers are different. Both PAL and SECAM operate with 25 interlaced frames per second, with 625 lines per frame. Just as with NTSC, some of these lines occur during the vertical sync, resulting in about 576 lines that carry picture information. Other more subtle differences relate to how color and sound are added to the signal.
The most straightforward way of transmitting color television would be to have three separate analog signals, one for each of the three colors the human eye can detect: red, green and blue. Unfortunately, the historical development of television did not allow such a simple scheme. The color television signal was developed to allow existing black and white television sets to remain in use without modification. This was done by retaining the same signal for brightness information , but adding a separate signal for color information. In video jargon, the brightness is called the luminance signal, while the color is the chrominance signal. The chrominance signal is contained on a 3.58 MHz carrier wave added to the black and white video signal. Sound is added in this same way, on a 4.5 MHz carrier wave. The television receiver separates these three signals, processes them individually, and recombines them in the final diplay.
譯文：
關(guān)鍵詞：核心，合成信號，電壓耦合
電視信號
盡管已經(jīng)擁有50年的歷史了,電視信號依然是常用的傳遞信息的途徑之一。圖 8.3演示了電視信號如何出現(xiàn)在一個示波器上。這叫做合成信號,意謂有垂直的方向和水平的方向的合成(同步)和真實的圖片數(shù)據(jù)混合的脈沖信號。
這些脈沖被電視接收器同垂直與水平線以及其他歪斜線路配和成信號并被電視顯示出來。標準的信號每秒包含30個完整的圖像,一般被做成了體格,電視工程師會把每個體格編制成包含525條行（電視專門術(shù)語）。因為在這些線中的只有80到486條包含了電視信號的數(shù)據(jù)；剩余39到45條行被同步脈沖保留用以維持電視能與信號一起同時被使用,所以這一個數(shù)字稍微具有一定的迷惑性。
標準的電視信號使用了一個被交織的格式以便減少顯示時圖像的閃爍。這就意謂著每個體格中的所有奇數(shù)的線首先被傳輸,而那些平坦的線然后跟隨著被傳輸。那群奇數(shù)的線被叫做奇數(shù)領(lǐng)域, 和另外一群線叫做平坦領(lǐng)域。由于每個體格都是由二個領(lǐng)域組成,并且每秒以60個領(lǐng)域的速度進行信號傳送。由一個復(fù)雜的連續(xù)垂直的同步脈沖長1.3個毫秒領(lǐng)域開始。這與跟隨線或電視的平坦或奇數(shù)的線相結(jié)合。每條線的速度為63.5個微秒,包括一個10.2微秒的水平線以同步脈沖持續(xù),分開并從下一個階段排成一行。在每條線里面,類比電壓符合圖像的灰色刻度,由較明亮的線在水平方向中遠離同步脈沖。在超過黑色的范圍這一個地方同步。在電視的專門術(shù)語中，同步脈沖被說成是比黑色的線更具有黑色性。
作為電視的信號類比到轉(zhuǎn)變?yōu)閭魉托盘柕挠布凶鲆粋€體系的核心。通常是以一張的形式插入到一部計算機中,而且經(jīng)由一個同橋電纜線連接到一個攝像機的電子學卡片的形式。由來自軟件的指令之下，核心等候下一個體格的開始,如垂直的同步脈沖所指出。在下列各項領(lǐng)域的出現(xiàn)的時候，電視的每條線許多次被抽取樣品,典型地以每線512,640或720個三種樣品,每樣品8B。這些樣品被儲存就像傳送圖像一樣被記憶.
這樣獲得的傳送圖像造成在垂直和水平線之間的一種明顯的不同方向。每個在數(shù)傳圖像中符合電視的信號排成一行,并因此在電壓耦合元件中輸出。然而，信號并不是如此垂直。在電壓耦合元件中，每排包含在約400和800之間輸出,依賴一種被用的特別裝置。當從電壓耦合元件讀出來時,電視的產(chǎn)生線進入平滑的類比信號之內(nèi)然后被過濾, 如此就如在圖 8.3 中所顯示的那樣. 換句話說，電視信號并不依賴信號在電壓耦合元件中存在的多少。水平的方向被限制類比信號有多快的速度決定了其是否允許被改變。這通常是以 3.2個百萬赫茲為彩色電視放置,造成上升時間大約 100個十億分之一秒,i.e,約 1/53.2 微秒中的第 500個電視信號線。
當電視的信號在核心中被數(shù)字化的時候,然而,它被轉(zhuǎn)換返回專欄,被數(shù)字化了的圖像專欄沒有關(guān)系到電壓耦合元件的專欄。數(shù)傳圖像的專欄數(shù)字獨自地依賴核心抽取樣品許多次電視信號的每條線。舉例來說，一個電壓耦合元件可能每一排有800得好,當被數(shù)字化的圖像只可能有每排 512個圖素 ( i.e,專欄) 的時候。
被數(shù)字化的圖像專欄的數(shù)字也對另外的一個非常重要的理由。標準電視圖像要占3/4,也就是,有些稍微寬有些稍微高一些。體育照片就有9/25的寬度比。作為科學的申請電壓耦合元件時常用1：1的寬度比，i.e ，就是一個完美的正方形。無論如何，電壓耦合元件的方向比被電極的安置調(diào)整,而且不能夠再被改變。然而，被數(shù)字化的圖像方向比依賴每條樣品線的數(shù)字。當圖像在電視監(jiān)視器上或在顯示器中被顯示的時候,這就變成了一個問題。如果這方面不能被適當?shù)卣{(diào)整,圖像容貌就會水平方向或垂直方向壓扁。
信號在這里描述的525行電視信號被稱為國際電視系統(tǒng)委員會(國家的電視系統(tǒng)委員會),一個標準一直到1954定義了其方法。這是沿用于美國和日本的系統(tǒng)。在歐洲有二個被稱為可程序化行列邏輯(時期交互線)和SECAM 的相似標準。(繼續(xù)影象和記憶)他們基本的觀念是相同的,只是數(shù)字不同而已?？沙绦蚧辛羞壿婼ECAM 操作由于25使其交織成了一秒體格,由每體格 625條行。 正如國際電視系統(tǒng)委員會所說，一些線在垂直的同步期間發(fā)生,大約造成進位畫數(shù)據(jù)的576條行。其他的較敏感的方面不同例如如何把顏色和聲音增加到信號之中。
傳輸彩色電視的最直接的要求要有三個分開的類比信號,一為人類的眼睛能發(fā)現(xiàn)的三種顏色:紅色,綠色和藍色。然而，電視的歷史發(fā)展并不是一個如此簡單的方案。彩色電視信號被發(fā)展并允許存在于黑白的電視，其設(shè)定在沒有修正的使用當中保存。這被稱為光亮數(shù)據(jù)并保有相同的信號,是增加一個分開信號為彩色數(shù)據(jù)。在電視的專門術(shù)語中，光亮叫做亮度信號,當顏色成為電視信號的時候。電視信號被包含在能增加到黑白的電視信號的一個3.58百萬赫茲的運送波上。聲音以相同的方式被增加在一個4.5百萬赫茲運送到波上。電視接收器分開這三信號，獨立地處理他們，并且最后在顯示器中結(jié)合他們。
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