The KS_DATAFORMAT_VIDEOINFOHEADER2 structure describes a video stream that includes settings for bob or weave.

Interlaced video images are made up of fields. Each field contains half of the number of lines needed to make up one frame of video. A field consists of either the even or odd lines of the original image. During interlace display scanning the screen is refreshed in two top-to-bottom passes such that the lines scanned in one pass are positioned between the lines drawn in the previous pass. Digital displays use progressive scanning, which means that they render all lines in a single top-to-bottom pass, which requires twice as much data per pass as interlaced scanning. Therefore, the video data format must be converted from one that is compatible with interlaced fields to one that provides progressive frames prior to rendering on a digital display. The process of translating received interlaced video signals into a progressive scan format for output and display on any digital display is called de-interlacing.

Interlaced Format versus De-Interlaced Format

There are two straightforward and basic methods of de-interlacing an interlaced video image for display on a progressive scan monitor: “ Bob ” and “ Weave .”

" Bob " (intra-field spatial interpolation) is the process of completely discarding one of the fields in an interlaced video data. Either all the odd or all the even fields are discarded. Using the fields that remain, interpolation is performed between the lines to generate an entire non-interlaced frame for the progressive scan monitor. This method includes no reference to the discarded fields.

" Weave " (merging) is the process of combining the odd and even fields of an interlaced video image to generate the entire non-interlaced frame for the progressive scan monitor.

Each method is simple to implement and has been around in the video industry for some time now, but each introduces some visual artifacts which leads to poor image quality.

Bob and Weave

" Bob " works well for images that are in motion but not for still images. If, for example, interlaced video is 480i (NTSC format), then the Bob method would just use the 240 scan lines of either the odd or even field and interpolate between the lines to generate a non-interlaced 480 line frame for the progressive scan monitor. The result is that the vertical resolution is decreased by half. Although this method works well, it can produce shimmering artifacts which create fuzziness and loss in detail in the vertical picture resolution. Artifacts are most obvious when text and stationary objects/logos are overlaid on live video. On some images objects may appear to bounce up and down. These artifacts may be worsened with frame rate conversion, such as converting from 60 Hz to 72 Hz.

" Weave " is perfectly adapted for still images because it uses all of the information available and thus generates the best possible image. While it works well with still images, it creates annoying feathering (combing) artifacts with motion video. Fast video and text scrolling can become unbearable. Commonly known as “feathering,” the vertical edges of moving objects in the image look like feathers. When an image is moving, any attempts to weave the fields will result in significant motion artifacts. Because the recording is performed in an interlaced manner, the two source fields that make up a complete frame are not recorded at the same time. Each frame is recorded as an odd field from one point in time, and then as an even field recorded 1/60 of a second later (for NTSC). A car moving at 60 mph will move by almost 1.5 ft. in this time, so that vertical edges in the odd and even fields will be separated by an equivalent distance. Simply combining fields causes the errors in the image called “combing” or “feathering” artifacts.

A simple solution to the problem of deciding whether to implement either the “bob” or the “weave” process is to switch between the two processes, depending on whether or not there is motion between the two fields. On a field-by-field basis, using a simple motion calculation, this technique would detect when the image is moving and implement the “bob” process and detect when the image is still and switch to the “weave” process. This sounds like a good solution to the “bob” or “weave” options that result in visual artifacts; unfortunately, most frames contain a mixture of both motion and still images, and whichever process is selected, artifacts are possible in those portions of the image for which the process is not optimized.

First introduced with DeltaChrome processors and further refined for Chrome S20 Series processors, S3 Graphics' Chromotion provides a more precise technology to determine the optimal scanning process, and provides superior de-interlacing.

Because most images contain a mix of still and moving regions, Chromotion's per-pixel adaptive de-interlacing technology looks at fields on a pixel-by-pixel basis and optimally determines whether to “bob” or “weave” on a pixel-by-pixel basis, based on the detected motion for that precise pixel. This advanced algorithm looks at pixels from the previous field, from the next field, and from the current field, and mathematically determines if there is motion. Thus it generates an appropriate, corresponding pixel for the current frame. Because this superior algorithm looks at the image on a pixel-by-pixel basis rather than on a field-by-field basis, it eliminates the visual artifacts in moving objects and preserves full resolution of non-moving portions of the screen. The result is a high quality crisp image, even on a HDTV progressive display.

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我们在观看DVD影碟的同时会发现一般DVD都有两种Video Mode,也就是weave和bob模式！  
什么叫bob呢？  
观赏 DVD 时，从隔行信号编码而成的影片内容将使用 bob 模式播放，这是一种不同于 weave 方式的消除隔行技术。  
Bob 以两倍于画面速率播放影片内容，而各个画面只显示某一场。这将使影像略为上下抖动，尤其是显示文字时，  
不过这种方法可消除水平纹影。bob 模式仅适用于 NTSC/PAL 影片内容，如预告片。  
而weave又是什么呢？  
为了消除隔行格式，weave 模式将默认为 DVD 影片的播放模式以确保画质。如果检测到隔行影片内容即会切换至   
bob 模式，因为将在播放隔行影片内容（内含诸如预告片的 NTSC/PAL 非影片内容数据）时看到水平纹影。  
其实，这里边也有个小窍门配合weave和bob判别DVD是否DECSS，现今大多数美国影片在制作成DVD时，一般是  
weave模式，如果你发现该影片的Bitrate是9.8或7.5(特指大多数情况下),而且屏幕为可变形16:9的时候(可在16:9和4:3 
下任意切换)，基本可以判定此为具有收藏价值的DECSS碟。不过也有欧洲的部分影片或比较旧点的影片是bob模式的  
DECSS，所以这个方法并不是万能的，对于新近制作上画的美国影片来说，这个方法倒有90%的成功率。 :) 

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BOB和WEAVE都是将视频/影频转换成逐行的一种方法，只是一般而言WEAVE针对影频源，BOB针对视频源，会各自得到较好的效果 

至于“视频源”和“影频源”分别是指Video mode(摄像模式)像源和Film mode（电影模式）像源。是制作dvd的两种视频素材来源。

Video mode，通常指用摄像机拍摄的，如电视，以ntsc为例，每秒拍摄60场，先是1,3,5,...,525奇数行扫描线1场，再是2,4,6,...,524偶数行扫描线1场,这两场合起来才是完整的一个画面帧，

由于视觉暂留，看起来好象是一个完整的画面。实际上，因为这两场的拍摄是有时间差的，除非是静止的场景，否则如果简单地用weave法把两场拼在一起合成一个画面，是会有锯齿的。 

Film mode，就是电影，按每秒24帧拍摄，每个画面拍摄时本身是完整的，制作dvd时再拆分成两个场，以后用weave算法把两场拼在一起当然是天衣无缝。