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1. Regarding 1080i/1080p, it's a very long convoluted process. 2. Why 120 Hz TV's are so special:(ZT)

本文发表在 rolia.net 枫下论坛Regarding 1080i/1080p, it's a very long convoluted process. Here's the theory:

Typical HDTV's operate at 60Hz (meaning the screen 'refreshes' - redraws itself 60 times per second), except the newest TV's which support 120 Hz. Retailers like to advertise 120Hz as having fast fluid motion (like the latest Future Shop ads) - gag! Movies are filmed in 24 frames per second, and typical sports over the tube are sent in 1080i at 30 frames per second.

Since the DVD days, in order to display DVD (and now HD-DVD and Blu-Ray) on TV's and HDTV's, you have to convert the native 24 frames per second video to 60Hz. This process is called "3:2 pulldown." This is important.
----------

What 3:2 pulldown does is convert 24 frames per second film to 30 or 60 frames per second, which is what the TV operates at. In order to do this, it has to do some frame combining. Note I don't know this process exactly, but this is basically the gist of it:

Let's look at the first two frames of a video. Call frame 1 "A" and frame 2 "B" (there's 24 frames per second, so this is 2/24ths of a second).

3:2 pulldown at 60Hz will take Frames A and B and display them in this order: A, A, (A+B), B, B.

Notice that two frames were combined to create a smooth transition from frame A to frame B. Unfortunately, while without this step video would be very jerky, even with it there is some jerkiness, which is often called "judder" or "telecine judder" . A much better read can be found here:

http://en.wikipedia.org/wiki/3:2_pulldown#3:2_pulldown

-----------

Now, after that background, here is how 1080i looks exactly like 1080p on modern TV's:

Since 1080i is interlaced - it transmits half of a 1080p frame, then the other half, here's how it works:

Video is 24 frames per second. TV's work at 60Hz as mentioned before. What the TV does is combine each half of the 1080i signal internally, perform 3:2 pulldown, and voila - a 60 Hz recreated 1080p video is born! Since the video itself is only 24 frames per second, and the TV's redraw 60 times per second, it's not very difficult to recreate a 24 fps image that's trasmitted at 1080i (ie it's transmitted as 48 half frames per second)

Why 120 Hz TV's are so special:

OK so in my previous section I tried to explain to the best of my ability how 1080i is converted to 1080p in modern HDTV's, as well as the jerkiness - judder, that happens by converting 24fps film to 30/60 Hz internally in the TV.

Some new TV's are advertised as 120Hz. What does this mean?

Simple: instead of redrawing the TV 60 times per second, it does it 120 times. Whoopy doo, right - film is only 24 frames per second!

But here's the rub: 120 is a perfect multiple of 24 (120 / 24 = 5). It's also a perfect multiple of 30 (120 / 30 = 4).

Guess what: film currently is either shot in 24 frames per second (DVD, HD media) or 30 frames per second (live TV).

When you have a 120 Hz TV that properly decodes a 24fps DVD/HD-DVD/BluRay, it performs a 5:5 pulldown (yes that's what it's called).

As long as the TV really is 120 Hz, this should, in theory, create absolutely no judder/jerkiness/whatever. Pretty sweet eh? Yeah, "true" 120 Hz TV's should be awesome, and it will be a must-have feature in the future.更多精彩文章及讨论,请光临枫下论坛 rolia.net
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Replies, comments and Discussions:

  • 枫下家园 / 家用电器 / 看高清电影有必要1080p吗?买了1080p HDTV的请试着放同一部片子1080p/720p的文件,能看出差别来吗?友情提供《色戒》电影预告片720p和1080p的下载
    • for sure 1080p is better than 720p. But it's hard from me to identify differece between 1080i & 1080p.
      • 看到国内有人用投影机试,说100寸的屏幕看不出1080p/720p有差别,至少要150寸以上的屏幕才能看出来
      • 你要是从电视信号上分别出来1080p/1080i.那就是神仙了
    • 扫盲过无数次了,因为刷新频率的关系,除了1920x1080的游戏,所有号称1080p的影像,包括BR/HD Disk, 只能以1080i还原。
      • 这个要扫盲一下,现代1080p HDTV由于采用了Deinterlacing技术都是Progressive扫描,因此所有1080p的影像,包括BR/HD Disk, 以1080p还原;所有1080i的影像,也是以1080p还原,差别肉眼几乎难辨。
        • 现在,还没有仪器的分辨力能够超过人的视觉辨别力,图像失真,想逃过人的眼睛视觉判断是很难的(人的音频判断容易被忽悠)。换句话说,任何技术,如果最终结果是“差别肉眼几乎难辨”,这样的技术就是失败的技术,这就是为什么视频产品比音频产品成本高的缘故之一。。。
          • 不明白你到底要说什么,这里“差别肉眼几乎难辨”指的是1080p电视显示1080i的影像,和1080p电视显示1080p的影像,有差别,但差别肉眼几乎难辨。。。如果你想知道怎样辨差别,我可以告诉你。。。
          • 人眼对颜色对比度和延迟反映的敏锐度大大高于分辨率,对於分辨率在一定距离后其差别可忽略不计,因为此时肉眼就算在静止图下也分辨不出两根靠的很近的平行线, 动态影像就更难分别,所以在50寸以下在2-3米平常距离中是无法区别的.多掏银子达到心里安慰而已.
        • 哪位明白人给批判一下这篇文章:THERE IS NO DIFFERENCE BETWEEN 1080i AND 1080p.我觉得他说的不对,但是不知道哪儿不对。貌似很专业的HDTV网站:
          • 区别肯定是有的,只不过一般看不出来,1080i影象的有效信息量只有1080p的一半,1080i隔行扫为了达到逐行扫的的效果只能靠复制或插值,这样一定有图像失真。。。
            • 那篇文章里说,不管是1080i/1080p对显示24frames/sec来说都是绰绰有余,还要再插入些多余的信息来补足,所以1080i/1080p所包含的实际有效信息是一样的。
              • 信息的重复并不能增加有效信息,1080i纵向有效信息少一半是一定能看出区别的,运动场景比如网球比赛就很容易看出来。
                • 实际有效信息是一样的,1080i并不是1080p的一半。
          • 以前看过一篇文章,toshiba请了些人看1080P和1080i的节目,没有人能看的出来区别;但是他们能很容易区分出来60hz和120hz的电视。
    • 专家说过无数次了,只要你能肉眼看见蚊腹内的脂油,就能看出1080p/720p的差别有多大。
      • 1080p和720p,在40寸以上的HDTV距离足够近时差别是可辨的,关键要放在一起比。
        • 这个同意! 有那位能用两台46以上的1080p TV,并排同时播放以上两个片断比较一下?
          • 真正的差别如果你蓝光DVD放专门的蓝光DVD影片,看上去会有差别,但是即时如此拿回家以后你也感觉不到差别
    • 我都看了一年多的HD了,说真的,除了网球比赛感觉HD的频道那个黄色小球更加清晰点外(还的可以对比非HD频道),真的肉眼每有什么特别感觉;色戒的高清晰版和普通版,也没有觉得汤唯的三点更黑。。。所以真的差别不大
      • 高清比标清(480p)在正常的视距内肯定有明显差别,你看不出来,只能说你的眼睛有问题.以前也遇到一个IT牛人,向我显摆他的高级Sony特丽珑显示器,我特意去瞻仰,发觉很闪,看属性设在60Hz刷新率,我改到85Hz,感觉很稳定,但这老哥并不觉得有不同
    • 要比就要在不同的基准上比----- 1080p的节目在720p和1080p的电视上分别回放。720p的节目也是一样。这样才看得出来。对了谁知道有没有只支持720P的电视?
    • 如果连计算机做显示器用就看得出来,如果看电影没什么区别。
    • 这个好比是选美,单个下面看一个个都挺美,说不上哪儿不好,上台放在一起比,差别就出来了,越看还越明显:-)
    • 个个都是空口说白话,有谁亲自动手亲眼观察过的?我已经提供了下载地址,连电脑试一下不很难吧
      • 你在电脑上看电影?
        • 用电脑连HDTV看1080p是最方便的,网上有大量电影下载。Rogers有线电视和Bell卫星都没有1080p的节目,连1080i的都极少(有待证实),绝大部分是720p。PS3、HD DVD的播放器毕竟不多,有也不都支持1080p,更遑论1080p的碟
          • 许多同学十年前没有机会自己购买电器产品。现而今就跟1998年一样,当时DVD机及碟片市面上很少见,一般人也买不起。偶尔拿到一张DVD,在SDTV上观看,效果比VCD也强不了多少。当然,五年后(2002)情况就大为改观,七年后(2005)
            我等用户就等不及用上了HDTV,当时Rogers有些HDTV频道都是免费的。现在,HDTV应该算是普及了,观看DVD没有任何问题。

            但,真正的1080P估计还得等到2012年。

            所以,现在讨论1080i vs. 1080p没有实际意义。片源质量决定一切。
            • 反正我现在只看普通的DVD碟片(碟子多得都来不及看),所以720P的对我来说已经足够了。
    • 1. Regarding 1080i/1080p, it's a very long convoluted process. 2. Why 120 Hz TV's are so special:(ZT)
      本文发表在 rolia.net 枫下论坛Regarding 1080i/1080p, it's a very long convoluted process. Here's the theory:

      Typical HDTV's operate at 60Hz (meaning the screen 'refreshes' - redraws itself 60 times per second), except the newest TV's which support 120 Hz. Retailers like to advertise 120Hz as having fast fluid motion (like the latest Future Shop ads) - gag! Movies are filmed in 24 frames per second, and typical sports over the tube are sent in 1080i at 30 frames per second.

      Since the DVD days, in order to display DVD (and now HD-DVD and Blu-Ray) on TV's and HDTV's, you have to convert the native 24 frames per second video to 60Hz. This process is called "3:2 pulldown." This is important.
      ----------

      What 3:2 pulldown does is convert 24 frames per second film to 30 or 60 frames per second, which is what the TV operates at. In order to do this, it has to do some frame combining. Note I don't know this process exactly, but this is basically the gist of it:

      Let's look at the first two frames of a video. Call frame 1 "A" and frame 2 "B" (there's 24 frames per second, so this is 2/24ths of a second).

      3:2 pulldown at 60Hz will take Frames A and B and display them in this order: A, A, (A+B), B, B.

      Notice that two frames were combined to create a smooth transition from frame A to frame B. Unfortunately, while without this step video would be very jerky, even with it there is some jerkiness, which is often called "judder" or "telecine judder" . A much better read can be found here:

      http://en.wikipedia.org/wiki/3:2_pulldown#3:2_pulldown

      -----------

      Now, after that background, here is how 1080i looks exactly like 1080p on modern TV's:

      Since 1080i is interlaced - it transmits half of a 1080p frame, then the other half, here's how it works:

      Video is 24 frames per second. TV's work at 60Hz as mentioned before. What the TV does is combine each half of the 1080i signal internally, perform 3:2 pulldown, and voila - a 60 Hz recreated 1080p video is born! Since the video itself is only 24 frames per second, and the TV's redraw 60 times per second, it's not very difficult to recreate a 24 fps image that's trasmitted at 1080i (ie it's transmitted as 48 half frames per second)

      Why 120 Hz TV's are so special:

      OK so in my previous section I tried to explain to the best of my ability how 1080i is converted to 1080p in modern HDTV's, as well as the jerkiness - judder, that happens by converting 24fps film to 30/60 Hz internally in the TV.

      Some new TV's are advertised as 120Hz. What does this mean?

      Simple: instead of redrawing the TV 60 times per second, it does it 120 times. Whoopy doo, right - film is only 24 frames per second!

      But here's the rub: 120 is a perfect multiple of 24 (120 / 24 = 5). It's also a perfect multiple of 30 (120 / 30 = 4).

      Guess what: film currently is either shot in 24 frames per second (DVD, HD media) or 30 frames per second (live TV).

      When you have a 120 Hz TV that properly decodes a 24fps DVD/HD-DVD/BluRay, it performs a 5:5 pulldown (yes that's what it's called).

      As long as the TV really is 120 Hz, this should, in theory, create absolutely no judder/jerkiness/whatever. Pretty sweet eh? Yeah, "true" 120 Hz TV's should be awesome, and it will be a must-have feature in the future.更多精彩文章及讨论,请光临枫下论坛 rolia.net