Is HDTV compression damaging picture quality?

Do your HDTV programs look as good as they should? If not, you may be seeing the results of overcompression. A growing number of viewers and experts are claiming that increased use of compression — technology that downsizes huge high-definition video streams for eventual reconstitution on your screen — is responsible for a drop in quality.

Such charges — aimed mostly at the two biggest cable providers, Comcast and Time Warner — have been echoing around the blogosphere in the wake of reports about new compression algorithms. Contributing to the debate: An AVS Forum member's tests showed that at least ten HD networks were more compressed on Comcast than on Verizon's fiber-optic-cable-based FiOS service.

While service providers insist that quality remains a high priority, some experts say competition has made channel quantity, not quality, the top priority.

It's no secret that most digital TV is compressed and decompressed--in some cases several times — not just by cable or satellite services and over-the-air broadcasters but also by the video cameras that create the programs and the network satellite systems that deliver them to distributors. Compression happens, too, in trucks, control rooms, cable headends, and other waystations along the signal's path to your screen. The telltale signs of overcompression include tiling, little colored blocks, and "mosquito noise," which looks like flaring fireflies. The crispness of the picture can suffer, too.

Quantity vs. Quality

Compressing huge HDTV video streams, however, allows carriers to deliver more of them. "Everyone's really fighting the same issue — limited bandwidth — [but] their offerings are more attractive if they give more channels," says Peter Symes, director of standards and engineering for the Society of Motion Picture and Television Engineers. "There are big arguments in the broadcasting community about whether you should use virtually the whole of the 19.2 megabits you get for a single HD channel to deliver really good HD, or whether by using other standards or more compression you can get away with a high-definition [signal] and one or two standard-definition [signals] or maybe sell part of it for data services."

Currently, quality is "minor to a vast majority of the viewing public, because the vast majority...doesn't have very big TV screens," HDTV consultant Peter Putman notes.

But those viewers who do are starting to notice, including AVS Forum member Ken Fowler of Arlington, Virginia, a self-described audio-video enthusiast who posted the results of his Comcast-FiOS comparison.

Fowler had dropped Comcast for FiOS, but renewed his Comcast service (while retaining FiOS) in order to get Washington Nationals games in HD, and he began noticing quality differences between the two services. Some of the Comcast channels, he says, "didn't have the same pop, the same level of contrast, and there was a lot more blurring during movement."

So Fowler began recording the same shows on both FiOS and Comcast with his TiVo; he then downloaded the files to a computer and calculated the bitrates based on file size. The differences ran from just 0.7 percent more compression on Comcast for HBO HD to a whopping 38.5 percent for Discovery HD Theater.

More-Efficient Compression?

Comcast acknowledges that it recently implemented additional compression of selected HD networks, but contends that its improved compression technology allows it to transmit three channels in the same bandwidth in which two were transmitted previously, without a loss of quality. Comcast's spokesperson adds that many comments about Fowler's AVS Forum post recognize that "our ongoing tweaking, if you will, and adjustments" are improving image quality.

Comcast isn't alone in looking to squeeze more HD into its cables. A Time Warner Cable spokesperson says that company is testing new increased-compression technology as well. On the satellite side, DirecTV and Dish Network are switching to a "more advanced compression algorithm," Putman says. Verizon FiOS, however, applies no additional compression to the network signals that it receives, a spokesperson says.

The HD broadcast format that a network uses can make a difference in the compression's impact. ABC and Fox are among those that use a progressive-scan format (720p), which Putman and other experts say tolerates compression slightly better than the interlaced (1080i) format used by CBS, NBC, PBS, and others.

Blu-ray Is the Benchmark

For consumers, the best HD experience will be with Blu-ray Disc content on a player hooked up to a display with an HDMI connector, which transmits uncompressed digital streams. "That's going to be the benchmark," says Symes.

If you're shopping for an HD service, Symes adds, "it's fairly a no-brainer: If you have FiOS or [AT&T's] U-Verse available, that's probably the way to go." Beyond that, so much local variability exists among competing cable and satellite services, he says, that the best idea is to ask friends in your area about their satisfaction levels.

But if you have an HD picture quality problem that you think is the result of overcompression, the best thing to do is to call your provider. Symes and Putman agree that overcompression and lowered quality will become an industry issue only when buyers who trade up to the biggest, highest-resolution screens notice and complain.

Join the PC World newsletter!

Error: Please check your email address.

Our Back to Business guide highlights the best products for you to boost your productivity at home, on the road, at the office, or in the classroom.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Louis Chunovic

PC World
Show Comments

Most Popular Reviews

Latest News Articles


PCW Evaluation Team

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Aysha Strobbe

Windows 10 / HP Spectre x360

Ultimately, I think the Windows 10 environment is excellent for me as it caters for so many different uses. The inclusion of the Xbox app is also great for when you need some downtime too!

Mark Escubio

Windows 10 / Lenovo Yoga 910

For me, the Xbox Play Anywhere is a great new feature as it allows you to play your current Xbox games with higher resolutions and better graphics without forking out extra cash for another copy. Although available titles are still scarce, but I’m sure it will grow in time.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?