鏡像驅(qū)動截屏技術(shù)在數(shù)字語音教室中的應(yīng)用

論文編號:TX256  論文字?jǐn)?shù):11313,頁數(shù):42 有開題報告，任務(wù)書

摘 要
 數(shù)字語音教學(xué)、遠(yuǎn)程教學(xué)等網(wǎng)絡(luò)應(yīng)用要求實(shí)時高效快捷地捕獲PC系統(tǒng)上的屏幕信息。采用傳統(tǒng)的API截屏方式，通過調(diào)用windows系統(tǒng)拷貝函數(shù)來截取屏幕信息的方法會耗費(fèi)大量的CPU資源, 本文采用鏡像驅(qū)動程序，在只耗費(fèi)5%—10%的CPU資源情況下每秒截取10至20幀屏幕圖像，達(dá)到實(shí)時捕獲PC系統(tǒng)屏幕信息的目的。
 這些新型業(yè)務(wù)的另一特點(diǎn)是，服務(wù)端會有流媒體視頻文件播放，接收端要能有連貫的視覺效果。在這種方式下，用傳統(tǒng)API截屏方式就會有以下幾個缺陷：1. 可能捕獲不到流媒體視頻畫面，這是因?yàn)橐曨l文件在播放過程中系統(tǒng)往往調(diào)用DirectDraw來加速視頻的播放，由于DirectDraw的特殊性，直接采用API函數(shù)來截屏的話，會捕獲不到視頻畫面信息。本文采用鏡像驅(qū)動，在設(shè)備層中就能捕獲到屏幕信息，Mirror Drive的好處就是可以直接利用硬件，達(dá)到用戶模式下讓人難以企及的“實(shí)時”，這是因?yàn)槭褂肂itBlt拷貝屏幕內(nèi)容，其數(shù)據(jù)需要從顯存?zhèn)鬏數(shù)较到y(tǒng)內(nèi)存，經(jīng)過低速繁忙的系統(tǒng)總線，自然比從內(nèi)存到內(nèi)存的數(shù)據(jù)拷貝慢得多。2. 嚴(yán)重浪費(fèi)網(wǎng)絡(luò)資源，一張1024*768屏幕位圖約為4M，每秒20幀就是80M，如此大的數(shù)據(jù)量在一些帶寬較低的鏈路上，極可能引起嚴(yán)重的通信瓶頸。本文采用JPEG圖像壓縮算法在視覺上不損圖像質(zhì)量的情況下將捕獲的位圖高效的壓縮，再將壓縮后的圖像傳輸給客戶端，即使有成千上萬的客戶端，也不會造成網(wǎng)絡(luò)崩潰。
 
關(guān)鍵字：鏡像驅(qū)動；位圖；API；DirectDraw；JPEG圖像壓縮算法
 
 
 
 
 The Application of Mirror-driven Screen Capture Technology in Digitized Voice Classrooms
 
                               Abstract
 Digitized Voice classrooms, distance learning and other network applications require real-time high speed to catch on the PC screen information. Traditional API methods, By calling the Windows system function to copy the interception of the screen information will consume lots of CPU resources, In this paper, mirror driver, only 5% -10% of the cost of CPU resources per second interception of 10-20 screen images, achieve real-time PC screen capture information purposes.
 Another feature of these new businesses is the server will be Video Streaming Media Player, receiver must have a coherent visual effect. In this way, using traditional API methods will have the following shortcomings: 1. Can not catch the streaming media video images. This is because video broadcast in the process of systems are often called DirectDraw to accelerate video broadcast Due to the special nature of DirectDraw, the API used directly to the province, Video capture will not screen information. In this paper, mirror-driven, the equipment will be able to capture layer of the screen information, Mirror Driver advantage is the direct use of hardware, user mode to make the enterprises and the "real-time", it is because the use BitBlt copy screen contents Its data transmission needs from memory to memory, after low-speed busiest bus, natural than from memory to memory to copy data much slower. 2. A serious waste of network resources, a 1024 * 768 pixel screen bitmap is about 4M, 20 per second is 80M. Such a large volume of data transport in some low bandwidth link, is very likely to lead to a serious bottleneck in communications. In this paper, using the JPEG image compression algorithm in the visual without compromising the quality of images will be captured under the bitmap efficient compression, and then compressed image transmission to the client, even if there are thousands of clients, will not cause the collapse of the network.
 
Keywords: Mirror drive; Bitmap; API; DirectDraw; JPEG image compression algorithm

目錄
1 緒論 1
1.1 課題來源 1
1.2 課題目的和意義 1
1.3 課題解決的問題 2
1.4 本文的組織結(jié)構(gòu) 2
2 相關(guān)技術(shù)知識介紹 3
2.1鏡像驅(qū)動截屏技術(shù) 3
2.1.1 Mirror driver簡介 3
2.1.2 Mirror driver驅(qū)動原理 5
2.2 位圖文件格式 6
2.2.1 位圖文件頭 7
2.2.2 位圖信息頭 7
2.2.3 調(diào)色板 8
2.2.4 圖像數(shù)據(jù) 9
2.3 圖像壓縮算法 9
2.3.1 圖像壓縮步驟 9
2.3.1 普通JPEG壓縮算法 11
3 系統(tǒng)模塊功能的實(shí)現(xiàn) 13
3.1安裝Mirror driver 13
3.2 屏幕捕獲 16
3.2.1 全屏捕獲 16
3.2.2 位圖的保存 17
3.2.3 區(qū)域截屏 19
3.2.4 截屏效果 20
3.3 位圖壓縮及顯示 22
3.3.1 按指定質(zhì)量將位圖壓縮為JPEG圖像 22
3.3.2 壓縮后圖像的顯示 27
3.3.3 位圖壓縮效果 28
3.4 圖像的連續(xù)顯示 29
3.4.1 使用定時器SetTimer 29
3.4.2 使用Sleep( time )函數(shù) 30
3.5 圖像連續(xù)顯示效果 32
結(jié)論 34
致謝 35
參考文獻(xiàn) 36