白白技术宅

3:2 Pulldown and Deinterlacing_2

本文由MagicAlex翻译自网站：

http://www.theprojectorpros.com/learn.php?s=learn&p=theater_pulldown_deinterlacing

此博文供大家学习交流。本人翻译水平有限，有什么专业性术语、概念出错也是应该的哈。英文原文与译文对照编排，方便理解离谱的译文。

 

本文适合了解一定场，帧，扫描类型，制式概念的同学阅读。遇到不理解的概念又找不到相关信息的苦逼同学，请在博文后评论处留言。

正文：

You may now be tempted to say, “well, that was easy”, but hold on. We now have a new situation to consider.

你可能会忍不住说“这不是比挖鼻屎还简单吗”，要齁住呀，同志。我们得考虑其他情况呀！

 

As we’ve mentioned before, NTSC video might

正像先前说的，NTSC制式的Video可能

have originally been converted from film. Film is, by nature, already progressive scan (a full frame), but is

是由电影film类型转化而得。而film是本身就是逐行扫描（完整图像），

captured at 24 frames per second, while video is captured at 30 frames per second (60 fields per second) in

只因为它是24帧每秒拍摄的，另一方面video是每秒30帧的哟（也就是每秒60场），

an interlaced format. This means that there has to be some creativity involved in converting the progressive

交错的格式。这差别意味着把逐行视频转化为隔行需要

film into interlaced video, due to the timing difference. Here’s how it works.

创造性，也肯定是复杂的，因为它同时又要要解决同步问题。下面就介绍它如何工作。。

 

Every frame of film has to be split into fields. Two fields per frame are needed for video. The first film

每帧拆分成不同数量的场，每帧两场是video的要求。Film的第一帧

frame is used for the first three fields, or frame-and-a-half, of video. The next film frame is used to

被拆成video的最前面的三场，也可以说一帧半。然后下一帧被

make the next two fields of video.

拆成video的后两场。

 

This continues at a three fields, two fields rate. It looks like this:

就这样继续下去，拆3场，拆2场。。。图示：

Obviously, certain video frames don’t add up (they come from two separate frames of film), but remember that

明显的，正确的video帧并没有加入（加入的是来自film的不同的两帧的2场），但是记住一点，

this is for display on an interlaced television. Because you never actually see a complete frame on an interlaced

这是在交错电视上播放的。因为你永远不能看到完整的一帧在交错的

television, your eyes can’t see that the frames might not match up — much in the same way that motion

电视上，你的眼睛没有能力看清video那些帧是匹配不上的 — 同样的不能看清动作场景

doesn’t match up in video. This process for converting film to interlaced video is called 3:2 pulldown.

也不是匹配正确的。这转化film向交错的video的过程叫做：3:2 pulldown。

 

There is a problem though. You cannot use the same deinterlacing techniques here as we used for video.

可是这里还是存在问题。你不能一直使用先前提到的反交错技术。

 

What happens if we change scenes from frame A of film to frame B of film? The second frame of video

如果在帧A过渡到帧B时刚好是在变换场景呢？那么video的第二帧

would have information from two completely different scenes! You can’t simply look at the two scenes

就会有来自完全不同的两个场景的图像信息了！而你不能简单地将两个场景

and add them together or figure out an average. You actually have to reverse the 3:2 pulldown process.

平均平均，把平均值加进去。实际上你不得不需要反3:2pulldown操作。

 

Here’s a diagram of how that is done:

以下是反操作的图解：（P.S.专业术语：场匹配反交错）

Looking at the diagram above, you can see that the deinterlacer first finds the original two interlaced fields

看看图示，你能看到反交错先找到由film第一帧形成的交错的场，正确的3选2，

that made up the first frame of film and combines them. It then displays the first full frame of film as the

再组合相加它们。然后再显示film的第一帧全景

first three frames of progressive scan video. It does the same thing with the second frame of film, but displays

作为逐行扫描的video的前三帧。它接着对第二帧做相同的事情，

it as two frames of progressive scan video. The next film frame is displayed three times again, and so on and so on.

只不过显示了作为逐行扫描的后两帧而已。Film的下一帧又显示为3倍，以此循环下去。

 

This works because progressive video is displaying 60 full frames of video per second instead of 60 fields of

这样的工作是因为逐行的video是每秒显示完整的60帧的，而不是。

video per second. The end result is a very smooth image without any deinterlacing problems. The slight

每秒60场的video。最终结果就是每帧都很平滑，没有任何的反交错不良的问题。不良的地方

downside is that because it is displaying at a rate of three frames — two frames- three frames, the video

在于它显示是3帧-2帧-3帧。。。这样，video就会

has a slight “judder” to it. Although at 60 frames per second, it’s almost indistinguishable.

有一定的“抖动”（P.S.停顿）。即使它是60fps，那也是几乎不能忽略的。

 

In order to create a great progressive scan image, the deinterlacer must efficiently perform deinterlacing

为了产生完美的逐行扫描的图像，反交错还必须得有较高的效率,

of both video and film. The other thing the deinterlacer must excel at is to know when it is looking at

不管是video还是film。另外反交错得必须擅长于播放时的

film-based material and when it is looking at video. If it can’t do that well, then everything else is rather

film视频或者video。（P.S.就是说播放时的反交错）如果做不好这一方面，那么其他方面就没有任何

moot, because the deinterlacer might try to render film-type deinterlacing on video (which simply

意义了，因为反交错可能会尝试在video上用film视频的反交错方法（这样就没有反交错

wouldn’t work) and video-type deinterlacing on film (which again would exhibit serious problems).

效果了）和在film视频上进行video的反交错步骤（这还会加重交错的程度）

 

When purchasing a display device for home theater usage, make sure that the deinterlacer is of the

当你为家庭影院购买显示器时，要确定它的反交错

best quality. Company names to look for would be Faroudja and Silicon Image.

最好的质量。Faroudja与Silicon Image公司是你要找的好地方。

 

P.S.文章少说了删除重复帧的步骤，这样就可以生成原始的film了。