A Short Version of the Long History of Television
...or What All Those Numbers Mean
...or Why High Definition is Better
- By Steve Puffenberger, Advent Media, Inc.
Philo T. Farnsworth was the inventor of modern television. While plowing a field one day in the 1920s, he conceived of a method of transmitting pictures over standard radio waves that will remained in use until 2009. Interestingly, immediately after his TV system was accepted, he began working on a High Definition system as early as the 1950s, but it was not accepted, and he began working on ways to harness nuclear fusion as a power source. (See www.philotfarnsworth.com.)
NTSC – the US Television Standard – until now
So we begin the discussion of the evolution of television with what Philo invented, analog TV. After a while the National Television Standards Commission created the TV “standard” for the US. Based on AC power line frequency of 60Hz (cycles per second), the system uses a “raster” of 525 lines which get redrawn 30 times each second. Each line has varying voltages that the TV receiver interprets as light or dark sections of the line, and so an image is formed by a cathode ray tracing in a zigzag pattern on the phosphor screen of the tube. (Actually only about 480 of those lines are visible because most TVs overscan the image to compensate for curvature in the picture tubes. The rest of the lines are used for vertical interval sync, and in the modern era time code and closed captioning. The number 480 is important as you will read later on.)
To reduce the bandwidth necessary, engineers chose to “interlace” the raster lines. Starting at the top in the first 60th of a second, every other line is drawn on the screen – which is known in the industry as a “field.” Then in the other 60th of a second the other field is drawn. This interlacing makes it so that thin lines or patterned clothing seems to “jitter” on the screen.
Interlacing was the first “compression” technique applied to video, and it allowed broadcasters to send a respectable black & white TV image to living rooms across America, ushering in the television age.
Other improvements to the NTSC TV system were made over the years, allowing for the addition of color and stereo audio, and the basic NTSC 525 line 60 field system continues in use in VCRs, DVDs, cable and satellite systems, and digital converter boxes long after analog TV was shut off in 2009.
Lines of Resolution
But I’m getting ahead of myself. In analog TV, we discuss the quality of any particular piece of gear in terms of “lines of resolution.” That’s because pixels hadn’t been invented in Farnsworth’s day, and lines of resolution also apply to film, as seen on theater screens.
The TV image has 525 horizontal lines, but in analog TV, there are no vertical “lines.” Instead it’s a continuously varying voltage. The more “bandwidth” you have, the more variance in voltage you can have on a line, hence higher “resolution.” Modern analog TV cameras are capable of extremely high resolution, but reality kicks in and one quickly runs into the practical limitations of transmission or recording because of the wires, switching gear, broadcasting frequencies or recording mechanism.
To explain horizontal resolution, imagine taking a picture of a picket fence. You see black and white vertical lines. Zoom out or pull back to fill the screen with pickets, and just before they all turn to “mush” (where you can’t distinguish between pickets), count them. There you have your horizontal lines of resolution number. Here are some typical numbers
- 35mm Kodachrome slide: about 4000 lines
- 35mm movie film frame: around 1,000 lines
- Broadcast cameras: around 700 lines
- Average consumer single-chip camcorders: around 300 lines
Then you have bandwidth limitations of the transmission or recording media. Even if you have the best, highest resolution camera, the “pipeline” can degrade a signal terribly. Here’s what’s typical:
- Betacam broadcast-quality tape 500 lines
- SD analog broadcast transmission signal 300-400 lines
- VHS tape – 250 lines
With analog video, as with any analog recording, there is also generation loss. When electronic editing came into being, editing became a matter of copying from tape, to tape, to tape. Usually masters were 3rd or 4th generation, so by the time all the editing was done, your 500 line master probably would only resolve around 350 lines. (Remember that number.)
Contrast that with 35mm film, where you have at least 1,000 lines of horizontal resolution. (Now you know one reason why TV producers use film instead of video for TV series production.)
Digital Revolution
Several years ago after mastering digital audio on CDs, developers figured out that digital would be the way to go for video, because you could copy without generation loss. So like squeezing new wine into old wineskins, they set out to adapt the NTSC 525-60 format into the digital realm.
Digitizing video is just like digitizing audio. The analog voltage is “sampled” or measured at sub-microsecond frequency, and given a digital value of 1s and 0s. Video is just a lot more complicated than audio, where you simply time-slice the audio voltages and give them digital values.
What they came up with was a raster made up of pixels. Digital video is a stream of digital photos, or “bitmaps” if you know that term from computer graphics. Instead of lines with continuously varying voltages, we now have a grid (raster) of “pixels,” or picture elements.
The best way to think of this is to think of a bathroom wall with square ceramic tiles. Each tile represents one pixel, and each pixel has 24 bits (ones or zeros) 8 red, 8 green and 8 blue (this is also known as RGB). 3x8=24, so this is often referred to as “24-bit color.” The way the math works out on this, each bathroom tile can be any one of 16.7 million colors. Now if you look at the whole wall, it becomes a mosaic of tiles that change color all the time. Think of the grand mosaic artwork you’ve seen. When you get far enough away the tiles disappear and you see the image. That’s how digital video (and photography) works.
But wait, if NTSC video provides an infinite horizontal resolution over 525 lines, we’re now looking through a screen door with pixels forming columns as well as lines. The adapters of digital video chose 720 x 480 pixels to form the 4x3 aspect ratio grid for NTSC video on DVD and digital videotape. (That is 720 vertical columns of 480 rows of pixels.) This is known as a “fixed raster” system, since it cannot change. And remember those 525 lines? Well the extra 45 lines you can’t see are added back in by the digital-to-analog converters before they’re recorded to tape or broadcast.
Because the definition of horizontal lines of resolution is where you can discern the difference between a light and dark vertical line, this means that the standard-definition digital video resolution is half of the number of vertical rows – in this case 720/2, which yields 360 lines of horizontal resolution – no matter how good your cameras are. (Does that number sound familiar?) Since it’s within the “broadcast standard,” and it wouldn’t degrade as it was copied, it was good enough. Now virtually all SD TV programming originates in this digital format.
(Interestingly, while the rest of the computer and graphic world uses square pixels, the grid of 720x480 for TV uses rectangular pixels to increase horizontal resolution. A 640x480 grid, which is the square-pixel equivalent, would be just 320 lines of resolution, while the 720 grid gives 360. And if you ever wondered why most Internet video looks so bad when blown up full screen, the most common streaming resolution has a horizontal resolution of only 160 lines! But with broadband Internet now popular, many streaming services are now supporting “high quality” and "high definition" playback which look much better.)
High Definition
Well, I could get into the geo-political issues involved in the 2009 switch to Digital TV (DTV), which includes High Definition TV (HDTV) but I won’t. My attraction to it stems from my years making slide-based Multi-Image programs, which had up to 4000 lines of horizontal resolution – remember Kodachrome? Numerically, we finally have a video format that gets closes to film! Here’s how:
The high definition numbers speak for themselves. Using a fixed raster, the HD standard actually has two prime resolutions in a 16x9 aspect ratio: 1280x720 square pixels, known as “720p,” and 1920x1080 square pixels, “1080i” or “1080p.” The “i” after a number means it’s interlaced, just like Farnsworth’s TV was. The “P” means “progressive”, and each row of pixels is drawn sequentially, like computer monitors work. Compare this with 480i (the new way to say “old fashioned TV” – also known as “Standard Definition,” SD, or SDTV), with a 4x3 resolution of 720x480, and you see there’s a HUGE difference in HD.
Now, getting back to those “horizontal lines of resolution”, remember it’s half horizontal pixel count. Whereas 480i delivers 360 lines of horizontal resolution, 720p delivers 640 lines; and 1080i/p delivers a whopping 960 lines! It’s awfully close to 1000 horizontal lines for theatrical film!
Start Big - Get Small
You’ve heard of GIGO, Garbage In-Garbage Out. By starting with a High Definition program, we can scale down to SD for DVD distribution or to streaming formats for Web or computer delivery quite easily. Because we have none of the artifacts or generation loss of analog standard definition, the SD reductions look better than ever! But, if you start with an SD signal and blow it up on a big screen digital TV, your mileage will vary!
Now here’s the wild part about the HD revolution. As the frame sizes and data rates have gotten bigger, cameras have gotten smaller! And the production pipeline has gotten simpler, since the new cameras record digital video from the get-go, and using Windows Media™ HD or Blu-Ray, the digital images are displayed on the screen without translation to analog. This makes the process so cost-effective, we’re actually able to produce HD content AT THE SAME PRICE POINTS as SD. This gives the video buyer unprecedented flexibility in delivery, whether it be for big screen projection, DVD distribution, PowerPoint™ presentations or Web video.
The Future
In June 2009, SD analog broadcast television was turned off in the US. The FCC has leased the frequency spectrum to police & fire, cell phones and other usages, so that’s the end of broadcast NTSC (except for a few low-power stations). ATSC is the American replacement for NTSC, and includes the two HD streams, and digital SD in its spec. Stations can broadcast one HD stream and multiple SD streams simultaneously and your ATSC tuner can discriminate them. But to use an old legacy TV, you now need a converter box for off-air programming. Also digital TV is all or nothing. You'll either get a great looking picture or nothing at all, so that's the end of the fuzzy fringe area reception - meaning far fewer people in rural areas can get over-the-air TV. That's progress for ya!
DVD and VHS will continue to be usable, as people can always play them on legacy TVs, and most new DTV sets have NTSC inputs. So your investment in media will not be wasted - though it might not look very good on a big new HDTV.
The High Definition Disk war has been won by Sony, and their Blu-Ray technology is becoming mainstream. Costs are declining rapidly on the ability to create Blu-Ray release disks, and players are becoming affordable, so this is now an option avaliable with our PainFree HD Video Services™.
But neither DVD nor Blu-Ray can play natively in PowerPoint™ or most other “slideware” presentation software. That’s why the Windows Media HD™ format is a great alternative. It can it be played in PowerPoint from the computer’s hard drive, standard DVD media or even Flash drives, – and replicated at a cost far below that of Blu-Ray disk.
So the future is filled with uncertainty as standards change very quickly. That’s why Advent Media focuses on helping you Communicate PainFree™, no matter what media you choose.
If you enjoyed this discussion of the history of video, you’ll probably enjoy the PainFree Presentations Book™, Steve Puffenberger’s book on how to do PowerPoint the right way.