Does anyone know if there is any way to discover whether Shaw broadcasts in full resolution HD or whether they use compression. I have noticed what appear to be compression artifacts on some HD channels (jerky picture as camera pans across a scene). Based on the level of service they have provided in the past I would be very surprised if we were getting full resolution HD even with the pitance of channels they offer.

Compression and resolution are two separate issues. However, the issue of compression by Shaw has been discussed many times and indeed they do compress the signals.

The max available (OTA and some service providers that don't compress) is 19.4 Mb/sec. Shaw provides roughly 13 Mb/sec in areas where they have 3 channels per QAM instead of 2. Broadcasters typically use 15-18 Mb/sec, although some that multicast may use less.

All cable / staellite providers compress HD signals to a certain extent. The only way to get pure, uncompressed signal is to get an OTA signal (Over-the-air). Depending on where you live, this may or may not be possible. You also need the proper gear, namely an ATSC tuner on your TV and roof top antenna.

Now, that being said, you are right about the fact that Shaw, even with the fact that they offer the least number of channels amongst all providers in Canada, compresses HD channels quite a bit.

The recommended bit rate for an HD channel should be 19.5 Mbits/sec and Shaw content is mostly delivered around the 12.5 Mbits/sec mark. It's no surprise you notice artifacts and I can tell you their HD channels used to look A LOT better 2 years ago.

Shaw is having serious bandwidth issues, which stems from leaving their archaic network untouched for so long and pocketing as much money (profit) as they could without keeping up with the times. The next year or two should prove whether this will come back to bite them, or if they will pull off some magic trick and be able to upgrade without causing an exodus of disgruntled customers.

All cable / staellite providers compress HD signals to a certain extent. This is NOT true. Rogers in Ontario does not compress the HD signals allowing up to 19.4 Mb/sec (2 HD channels per QAM). Many US cable service providers also don't compress HD. Videotron compress certain channels but not others.

While there may be a difference in PQ between OTA and cable, it's not due to compression if the service provider passes the full signal.

It's bad enough that Rogers used to operate on the west coast and we've had to make due with substandard service from Shaw while Rogers led the way in the east. Now I find that, in addition to Rogers having more HD channels and better more flexible STB purchase/rental plans, they are also providing a better picture as well. That TOTALLY sucks! Do any of the sat providers provide a better bit rate than Shaw (maybe grey market Direct TV is the way to go). :(

Canadian Satellite bitrate is usually around 15.

Compression and resolution are two separate issues.

Now that variances in compression has been well explained, can we agree that when the issue of resolution is being debated for the cases of the digital transmission of static images in HD format, there may also be a large variation in the quality of the image depending on whether or not the image has been re-scaled?

Assuming a static image is recorded in the studio in 1080 by 1920 and transmitted without any change in format, regardless of the degree of compression that may take place, will this static image appear on our home displays with the same PQ as in the original studio?

If I understand the principles of compression, the idea is to scan a single image for a large patch of adjacent pixels which have similar numeric values defining the tint and hue and then substitute a data structure that defines this patch while consuming much less data. The downside of this is that the substitution practice may erase the very subtle differences between the original pixels. This makes me believe that compression can also have an impact on the apparent resolution of a static image.

To preserve resolution of a static image in the face of compression, the original image would have to be composed of pixels where no two adjacent pixels are similar (by using a computer generated test pattern). The compression algorithm would then be foiled and delivery of the full 1080 by 1920 pixels would be obliged.

Knowing that very few homeowners have fixed pixel display devices capable of 1080 by 1920 pixels, it would not surprise me that cable and satellite operators have machines which reduce the picture quality of static images, as they clearly do for dynamic images, in an attempt to lower the volume of data that must be transmitted.

Lets discuss a few things.

1. I believe that most original HD cameras and most HD programming is actually limited to about 1500 horizontal lines, even though the maximum is 1920).

2. As mentioned, most HDTVs have less horizontal resolution than that anyway. See the Digtal Home FAQ on "Resolution" (under Help) (last paragraph) for "rough" numbers.

3. Some channels are 720P, therefore only 1280 horizontal.

4. BEV changes some 1080i channels to 720P, therefore 3 applies.

5. Cable companies that do not compress, do not "lower the volume of data", only companies that DO compress. This compression has nothing to do with "knowing that few homeowners have 1080p", it simply has to do with bandwidth limitations and economic considerations.

Let's do some math:
1080i is 1920x1080 at 30 frames per second.
The true bit rate is 1920 * 1080 * 30 * 3 * 8 = 1.5 Gbps.
I'm assuming 24 bits per pixel(?)
All transmissions need to be compressed. ATSC inherently uses MPEG2 to compress so saying that OTA doesn't compress is incorrect.
Like JPEG, MPEG allows the compressor to choose the level of compression, and obviously less is more.

We're discussing any compression "downstream" of the OTA (19.4 Mbps maximum) bitrate done by service providers. We know that the original HD stream is more than 1 Gbps.

The compression done by the service providers is "separate" from the compression done by the broadcaster (which can vary as some broadcasters multicast and provide bitrates as low as 12 Mbps (WNED Buffalo), while others don't and provide bitrates closer to 18 Mbps)

This is NOT true. Rogers in Ontario does not compress the HD signals allowing up to 19.4 Mb/sec (2 HD channels per QAM). Many US cable service providers also don't compress HD. Videotron compress certain channels but not others.

Thanks for correcting me on this. I realized we were both replying at the same time and while most of the information in my post is accurate, that part wasn't. You see what watching overcompressed HD singals everyday can do to you :rolleyes: ?

Can anyone shed some light on how Shaw's 13mb/s compares to a standard dvd. To my eyes HD is only marginally better than dvd. I probably wasted my money buying the highest resolution consumer CRT availbable (Sony KD34xbr960).
Gerry

As stated before, resolution and compression are separate issues. If there's not too much movement on screen, your TV will be able to use the Full 1080i x 1440 or so that the TV is rated for.

It's usually only when there's a lot of movement on screen that compression comes into play with compression artifacts.

DVDs have an upper limit of 10 Mbps, but most play at 4-9. Also, the bitrate can be varied, so you won't see any compression artifacts, because it's not live and can be encoded to eliminate artifacts.

DVDs are encoded as 480i.

The larger the screen - say 50"+, there would be more difference between HD and DVD.

In other words, for static images, compression does not change the resolution or the perceived resolution, ever? I don't care that the technical resolution doesn't change, I do care if edges are blurred because of compression. In other words, are the edges of people and blades of grass when I watch football any less crisp with high compression VS low compression?

It's not just the "edges" that are affected by compression artifacts. Depending on the original signal and what's being broadcast, the entire picture could be affected with compression artifacts like macroblocking.

For example, on nature programmes, water, fire and flocks of birds will have the whole screen full of macroblocking even at full 19.4 Mbps bandwidth. There is simply too much change for MPEG to "keep up". It seems to be worse with upconverted widescreen material. The colour red seens to be very noticeable for macroblocking.

Special effects like strobe lights and lightning also cause issues since the entire screen image changes several times in a short period of time.

Lets discuss a few things.

1. I believe that most original HD cameras and most HD programming is actually limited to about 1500 horizontal lines, even though the maximum is 1920).

2. As mentioned, most HDTVs have less horizontal resolution than that anyway. See the Digtal Home FAQ on "Resolution" (under Help) (last paragraph) for "rough" numbers.

3. Some channels are 720P, therefore only 1280 horizontal.

4. BEV changes some 1080i channels to 720P, therefore 3 applies.

5. Cable companies that do not compress, do not "lower the volume of data", only companies that DO compress. This compression has nothing to do with "knowing that few homeowners have 1080p", it simply has to do with bandwidth limitations and economic considerations.

Inspite of the fact that most HD cameras and displays don't exceed 1500 lines horizontally, if the cable company has chosen to compress, then if I understand you correctly, this compression will not compromise the fine detail in a static image.

I realize that the MPEG standard assures that a static image will receive all the 1920 by 1080 pixels that the format dictates. But wouldn't it be in the interest of the cable company to lower the quantity of data delivered for static images through the use of an electronic device and thus reap some extra gain by additionally reducing data volume beyond what compression of dynamic images would yield?

Given that few people would never notice the difference, I can't understand why the cable company would not be tempted by this approach.

We're discussing any compression "downstream" of the OTA (19.4 Mbps maximum) bitrate done by service providers. We know that the original HD stream is more than 1 Gbps.

And what's furthur ironic about the original 1 Gbps rate is that when its time for the STB to convert that 19.4 Mbps compressed bitrate back into a full digital frame, the HDMI (DVI) transmitter in the STB re-constitutes this back into a 1 Gbps stream which is split into three separate colour streams within the HDMI cable.

How closely the final 1 Gbps stream matches the original 1 Gbps stream is anybody's guess.

That is very true and is perhaps why some OTA STBs provide a better signal than Cable, despite no compression on some cable service providers.

There are also significant differences in the calibration of most HDTV inputs when comparing Component Video, DVI or HDMI.

What also can come into play is the conversion of the signal by some STBs. Although SA (and SA clone) STBs have a "passthrough" mode, most other cable and satellite STBs make you choose 720P or 1080i.

Then there is the conversion of the signal by the HDTV...

Currently, as I understand it, Vancouver is not in a good location to pick up Seattle OTB. Is there any possibility HD OTB will occur in Canada. (My Sony has a built in HD tuner that I'd like to take advantage of).
G

Currently, as I understand it, Vancouver is not in a good location to pick up Seattle OTB. Is there any possibility HD OTB will occur in Canada. (My Sony has a built in HD tuner that I'd like to take advantage of).
G
I beleive CBC Vancouver has a HD Trasnmitter. You should be able to tune them in.