Screen shot from Jericho: top is the whole frame, middle is detail from the HD frame, bottom is detail from SD frame When describing the differences between standard definition and high definition TV, I generally say that the higher resolution doesn’t so much deliver more detail, but that the detail that is there is cleaner and more nicely defined.

While that may be generally true, there are occasions when HD can deliver detail that is simply absent, or quite muted in SD. I noticed this last night when watching the fairly disappointing TV show, Jericho. Near the start there was a shot of a map. The texture of the map was beautifully defined when watching this scene on HDTV, even using a 720p projector. So I checked with an SD recording I had made at the same time, and there was some texture, but it was sporadic and only hinted at. So here are screen shots to illustrate the difference.

The top picture is the whole frame, shrunk down to 300 pixels wide. The middle picture is a 300 by 300 pixel detail of the HD image, while the bottom picture is from the SD image. I scaled up the 1,024 by 576 pixel screen capture of the SD image to 1,920 by 1,080 pixels, so the size would be the same, then grabbed the same 300 by 300 pixel detail.

I don’t really need to comment on the difference, do I?

The HD video was recorded on the new Strong SRT 5490 HD PVR, while the SD video was recorded on the new Topfield TF6000PVRt. I tranferred both via network connections to my computer and grabbed the screen shots using VideoReDo.

The HD was broadcast at a resolution of 1,440 by 1,080 pixels, while the SD version was at 720 by 576 pixels (VideoReDo rescales the horizontal size for the correct aspect ratio when you’re doing screen shots). Both were interlaced. The total bitrates were, respectively, 12.94Mbps and 6.07Mbps. The audio in the HD version was two channel Dolby Digital at 384kbps, while the audio in the SD version was two channel MPEG at 256kbps.

The uncompressed file sizes of the two screen shots, in TIF format, were 7.91MB for the HD version and 1.69 for the SD, yielding a ratio of 4.68:1. Using the actual broadcast resolution, the ratio is 3.75:1.

There was one downside to the HD broadcast. There was some conversation between two characters while they were driving along in the countryside. On the HD broadcast, this looked quite artificial because of the high resolution. The characters seemed pasted onto the background. This was far less apparent in the SD version. Clearly HD TV is going to force TV show producers to up the technical ante when it comes to green screen work.

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