Česta pitanja o HD-u

A. Dodatak

A.1 Distribucija ovog FAQ-a

If you wish to mirror this FAQ, please contact me The reason for this is not that I don’t want this FAQ to be distributed, but rather, I am planning to keep a record of all the mirrors for this FAQ, eventually on a separate page sorted by location (for faster access) and language. I will also need your details to send periodic updates and to ensure all mirrors are up to date.

A.2 Uvjeti i koncepti

Below are some terms and concepts mentioned in this FAQ, but not fully explained:

Codec – Coder Decoder. Basically a way to describe a piece of software or hardware that can decode or encode compressed video or audio.

CSS – Content Scrambling System. The form of copy protection used by DVDs, and famously (or is that infamously) hacked, which led to the MPAA DeCSS trials.

HDCP – High Definition Copy Protection. Now standard with every DVI/HDMI connection, HDCP requires both the source (player) and destination (display) to support HDCP if HD video is to be played, otherwise playback will fail or a low resolution image may be shown only.

HDMI – High Definition Multimedia Interface. HDMI is essentially DVI with (digital) audio. Ever popular with high end home theatre devices, it is starting to find its way onto mid-end and even some budget systems. Most devices, including some next generation game consoles (like the Sony PS3).

Interlaced/Progressive – On an interlaced display device (e.g. 1080i), at any one time, only half of the horizontal lines are displayed. This means that for each frame, every other line of information is displayed first (usually the odd numbered lines, called a “field”), and then the other lines, to make up the complete frame. For progressive display devices (or progressive scan), all the lines of information are displayed at the same time.

Similarly, when a BD/HD DVD player has interlaced output (eg. 1080i), half of the information for a frame is sent, then the other half. With progressive output, all the information for a frame is transmitted in one go.

The big debate is whether 1080p is better than 1080i, but there is no simple answer for this.

Well, there is a simple answer and basically for film based material connected to a 1080p display, in most cases, there is no difference in quality between using a 1080i connection or 1080p connection. The only difference is the order in which the information is sent to the display – the display should in most cases reassemble the information and produce identical outputs on the screen. This is for native 1080p displays. For lower resolution displays where down-scaling is required, this is where the confusion comes from.

The confusion comes from the fact that many displays supporting 1080i (for example, many plasma screens) have a native resolution of 720p – this means that no matter what kind of signal you send to the display (480p, 576i, 1080i …), it will be converted internally to 720p by the scaler and de-interlacer chip (if the input is interlaced) and displayed as such. Digital displays like plasmas and LCDs are all progressive displays.

Then you also have the resolution of the source and how the source was captured.

For content shot on film (movies), the image is captured in a progressive fashion. When this is stored in progressive fashion in an optical format like Blu-ray or HD DVD, then transmitting the signal over 1080i output simply means that the player will be sending 540 lines (half) of information per frame first and then the other half, and a good de-interlacer should be able to recombine (weave) the information again to form a 1080p picture. When the same signal is sent over 1080p, the display device does not need to do any combining and you also get a 1080p picture. However, if the de-interlacer on the display device is the cheap sort, then it might take the 540 lines and upconvert it to the native resolution, meaning you are only seeing half the resolution of the source at any one time – in this situation, 1080p is clearly better than 1080i – even 720p might be better. This AVS Forum thread might be of interest. This article goes into some more technical details.

Confused yet? To best illustrate what all the above means, here are some examples (focusing on high definition DVDs only playing back movies shot on film):

1. Playing back a Blu-ray/HD DVD movie on a 720p display through the player’s 1080i output. This is the most common scenario for current home setups (eg. high def DVD player connected to a plasma screen). The good de-interlacer on the display recombines the picture into a full 1080p picture. The scaler then scales down the picture to 720p resolution. If the de-interlacer was a cheap one, then you can get a fake 1080p picture by upconverting a half-resolution field, and then downconvert back to 720p – you are still not seeing more than 540 lines of information, half of what was stored on the disc. If the same display (with the cheap de-interlacer) somehow accepted a 1080p signal, then it would look better than the 1080i signal.
2. Playing back a Blu-ray/HD DVD movie on a 1080p display through the player’s 1080i output. The good de-interlacer on the display recombines the picture into a full 1080p picture. Picture is displayed as 1080p and looks just like it would if the player’s output was 1080p. If the display’s de-interlacer was a bad one (doesn’t do the proper recombining), then the 1080p signal would look better than the 1080i signal.

When every display accepts 1080p input, has a 1080p native resolution and your Blu-ray/HD DVD player outputs a proper 1080p signal, then things will be a whole lot simpler. Until then, a 1080p native resolution display with a good de-interlacer + 1080i input will give you a great 1080p picture. Of course there is still the matter of interlaced content (eg. HDTV), IVTC and the difference between NTSC/PAL displays, but let’s just leave it at that.

Sometimes you also see the 50i, 60i or 24p terms used after indicating a resolution. The number (50, 60 or 24) represents the frames per second (FPS), the i or p represents interlaced or progressive frames. PAL is 50i, NTSC is 60i and FILM is 24p.

Lossless/Lossy Compression – With normal types of compression, quality lost in favour of conserving space. This is called lossy compression, because the quality loss is gone forever. With lossless compression, the original quality is preserved when the audio/video is uncompressed, although this does mean that file sizes for lossless compressed content is much larger than that for lossy compression.

A simple analogy which can be used is the difference between JPEGs, which is lossy, and a ZIP file, which is lossless.

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