How come some channels look a lot better than others on my hdtv?

Question

I have HD channels. it looks awesome. thats not what Im talking about.

Im talking about, one cable channel (like animal planet, lets say) and fox and abc.

the fox and abc channels look so grainy and bad, its almost unbearable.

What is up with that? Is it the camera, the station, the way its broadcast, or a combination?

Answer 1

I higly doubt that the camera is makeing it look that bad , it is probably the way the cable station is broadcasting it to you, i would call the cable company and ask them about it.  they may need to swap out your cable box

good luck

Answer 2

The first problem is the cameras used to film HD content. NOT all HD cameras produce great, clear & sharp content. I see this on the local ABC (720p)  & NBC (1080i) news broadcasts. One report can be a great pic and the next (filmed with a different camera) can be grainy. The camera used does have a big impact on the quality of HD content.

The next issue is the cable companie's problem. They compress channels so much that it affects the quality of their content. Cable companies maximize profits by maximizing the number of subscriber channels on their system. Their profit motive leads to part of your problem.

Finally, digital broadcasts do have limited bandwidth and it is possible to momentarily lose some quality due to these limitations. These types of quality issues are usually seen following scene changes or during paning shots with lots of on screen activity or motion. It's possible to overwhelm the digital Mpeg compression alogorithum and creat on-screen pixelization (blocking), though this tends to be a momentary loss of quality.

Answer 3

The quality of digital channel (HD or otherwise) is dependent mostly on the compression rate chosen for that channel (with a cable system, it can differ from channel to channel).  Even blu-ray is compressed.  If you put the original data from HDTV camera on blu-ray, you'd only get about 90 seconds of the movie on one disc.

Also important is that FOX, ABC, and ESPN broadcast in 720p @ 60 full images per second (with good reason).  A lot of other channels (like Animal Planet) broadcast in 1080i @ 30 full images per second.  The resolution of 720 is lower than 1080; the number of pixels in a 720 image is 44% smaller than for 1080.  They can update a 720 picture twice as fast a 1080 one in the same amount of time on the same equipment.  Sports and action benefit from a higher display rate.  I'd rather see a smooth lower res image than a choppy high res one and 720 is so much better than the old 480.

Another problem is the cable company and the set top box.  If you using a standard box and the box is not set to output 720p @ 60 fps on a 720p channel, you may get the content upconverted to 1080i @ 30 fps.  I am afraid your set top box could be throwing away every other image (30 times per second instead of 60) and also add a little distortion because of the upscaling.

The cable company uses a lot of compression to broadcast the image with good reason because we don't have the infrastructure to transmit the whole thing all the time.

Your HDTV is most likely capable of about 2,230,000,000 bits per second (2.23Gpbs) but is not seeing a signal anywhere near that.  That's the amount of information per second needed to display  the image 1920x1080 pixels with 12 bits of luminence per pixel at 12 bit color depth with each pixel updated 30 times per second.  There are 24 bit schemes as well which would be about 4.4Gpbs.

Over the air broadcasts from TV antennas for one program will be at most 19,500,000 bits per second (19.5Mbps) because of the bandwidth relegated to the station by the FCC.  From 2.3Gbps to 19.5Mbps - that's a compression ratio of over 110.  There's a way to squeeze twice as much digital data into that same space with a technique called QAM but 19.5 x 2 = 41Mbps is the best you'd ever see at home right now (compression of 55).

There are further compression schemes which take the 19.5Mbps and take it down to 7 or 8 Mbps (a compression ratio of over 300!).  Cable companies can give more content and make more money by squeezing channels together.  I'm not sure digital content is as regulated as analog channels have been and the quality standards are not quite established.

Even blu-ray is compressed.  Blu-ray has about 5 time the storage capacity of DVD.  A DVD only stores about 4.7GBytes (37Gbits).  A factor of 5 higher would be about 200Gbits which at 2.3Gbps would be about 90 seconds of raw HDTV content.  A two hour movie (raw hdtv signal) requires about 2.3Gbps*3600s*2 (3600seconds in one hour) = 16,000Gbits.  The compression ratio on bluray is somewhere about 16,000/200 = 80