Video Questions and Answers

Here are some frequently asked questions about television and video. Some were originally posted on Internet forums.

Most of the information on this page pertains to legacy TV and video equipment, which uses all or mostly analog electronics and almost always uses a cathode ray tube (CRT) as the viewing screen..

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Articles on other subjects.

What is this 100 inch TV I see advertised in magazines?

You can make it yourself. It consists of a box big enough to hold an ordinary TV set, with a large magnifying glass in front of the TV screen. You can project the picture on a wall, a bedsheet hung on the wall, the ceiling (for bedtime viewing) or on a movie screen such as you use with a slide projector. The picture is quite dim but seems the brightest when projected on a movie screen.

Unfortunately the magnifying glass does not focus the middle and the corners of the picture very well at the same time so you have to compromise. Without buying it we have no way of knowing whether the kit you buy for about forty US dollars has a better lens than the magnifier you can buy in an office supply store like Staples.

You will have to experiment with the box size to get the best focus and the picture size you want. Also you have to turn the TV upside down. The TV might overheat when turned upside down but putting a small fan over the vent holes either on top of under the TV will help.

My rear projection TV has bluish green spots in the picture. I took off the screen panels and neither they nor the mirrors are dirty.

Check the red CRT and its lenses down below. Dust specks, when they block the red projected image, will result in greenish blue spots in the final picture.

It is possible for fungus to develop inside the fluid (used for heat dissipation) sometimes used inside the lens assembly of the CRT. If this is the case the lens, possibly the CRT itself if it is all one piece, has to be removed, drained, disinfected, and refilled.

It is mandatory that the fluid, if drained, be replaced with the proper kind of fluid. Otherwise not only will the focusing be incorrect but the CRT will suffer rapid "screen burn".

Hint: Yellow spots mean the blue projection CRT is dirty, purple (magenta) spots mean the green CRT is dirty. Depending on the color of the subject matter the spots may or may be seen. If you know how color mixing occurs with beams of light you can figure that out. For starters, if the subject matter is red, purple, or blue, purple spots due to dirt on the green CRT will not be seen.

There is a horizontal band slowly moving up the screen. After it passes off the top, another one appears at the bottom and starts moving up.

A line or band stretching across the screen and gradually moving up or down is not "(a) scan line(s)", rather it is interference of some kind. It takes work to track down. My present suggestion is, start by unplugging everything, absolutely everything, from the back of the TV. The plug things back in, one at a time, tos ee if/when the line comes back.

Try exchanging video cables to see if then a different device when connected makes the line come back. A cable might be bad.

If this doesn't help, also try moving the TV away from the wall or turn it facing another direction at least for a few minutes. Sometimes there is an electrical or electronic device inside or on the other side of the wall causing interference.

Also try arranging the video cables to not pass too close to power and audio (including speaker) cables, as best as possible.

Especially if other TV sets in the house are affected, try unplugging appliances including smoke detectors and VCR's and see if any one of them causes the interference when plugged back in.

A "surge suppressor" that plugs into the outlet and into which you plug the TV may help.

If you live near radio or TV broadcasting towers, microwave relays or transmitters, or cellular phone towers, you can experience more interference of this kind. Fear of interference is grounds to object to the installation of large electronic devices such as cellular phone towers in your neighborhood, sometimes the company must install gadgets including gadgets inside your home to eliminate this interference, or pay for cable TV for you.

I wish to feed the S-video output of my DVD player to two TV sets. Do they make a splitter to do this?

You really should have an amplified splitter but I don't know who makes them.

They make switch boxes to allow several devices -- DVD player, satellite TV box, etc. to feed the TV one at a time. One that handles S-video as well as composite video can be bought at Radio Shack for about USD 40. It could be connected backwards to feed two TV sets with one source. But it may or may not work, it depends on the exact electrical and impedance characteristics of the one S-video output and the two S-video inputs.

My setup uses some RGB switches to allow several sources to feed two monitors but one one source per monitor at a time.. Depending on the order I push the buttons, one output may feed both monitors for a moment. At that moment the video is very dim on both monitors but I have not examined it closely or long enough to find other degradation..

How Do I Evaluate DVD Player Anamorphic Downconversion (5/02)

Anamorphic downconversion, to recap, is the 4:3 Letterbox "TV Shape" choice on every DVD player to show16:9 enhanced DVD pictures correctly on a 4:3 screen.

You do not need anamorphic downconversion if your TV has 16:9 mode. On a 4;3 set, 16:9 mode is sometimes called the "squeeze trick". For this, leave the DVD player "TV Shape" set to16:9 all of the time.

If you are concerned about the quality of anamorphic downconversion, you probably have seen that it looks better using some DVD players compared with others. If you are familiar with video test disks such as Video Essentials or AVIA, you could bring one of them to the store after deciding on two or three "semifinalist" players.

Play a test pattern with several white horizontal lines two pixels thick on a black background. On Video Essentials play the 1.66:1, 1.78:1, 2.0:1, and 2.35:1 convergence grids, (frames 46613, 46614, 46615, 46616 on side 2 of the remastered laserdisk edition). On AVIA use the (letterbox geometry category) crosshatch 1.78, crosshatch 2.0 and crosshatch 1.78 patterns..

For all of these tests, leave the TV in 4:3 mode. Start with the player in 16:9 mode and make sure all of the horizontal lines are exactly 2 pixels thick (made out of two scan lines) and crisp. If not then try a different TV, the TV doubler or comb filter is interfering with the test. Now change the DVD player to 4:3 letterbox mode. If all the lines are still present and are one or two pixels thick (and other stuff you view looks good), then the downconversion is quite good. If some lines vanish completely or are four or more pixels thick including nearby dim lines then the downconversion could be a lot better. Repeat the test using all of the frames suggested above when checking for lines that vanish. Also for progressive scan DVD players, try all of the non-automatic film versus video mode choices, if any.

What is a "Digital TV"? (3/01)

We keep seeing advertisements and store displays about digital TV sets. The experts say that a digital TV set is one intended for HDTV and other digital broadcasts. Yet there are some digital TV sets with nothing digital inside them and others whose only digital components are used to simplify the handling of analog broadcasts. Here are a few facts worth noticing.

1. Although an HDTV broadcast is a digital signal when transmitted, most early digital TV sets did not tune in HDTV but instead require da set top tuner box purchased separately. The video signal fed into the set is analog and in a form comparable to NTSC or PAL as it exits the tuner box and is fed into the TV.

2. The tuner (channel selector) built into most digital TV sets received analog broadcasts only.

3. Unless it uses new technology such as LCD, DLP, etc. displays, the TV is built the same way as a regular TV, with the same kinds of analog circuitry. CRT picture tubes and their supporting circuitry are analog.

4. The set top tuner box can also deliver the digital TV broadcast to an ordinary TV set after converting ii to NTSC or PAL, etc. that the TV accepts.

5. TV sets with digital displays (LCD, etc.) also receive regular analog broadcasts.

The following are analog features of a TV (not all may be present): Component video input, S-video input, composite video input, VGA/RGB input, NTSC tuner, video amplifiers for signals coming in through any of the former, CRT's (picture tubes), cheap comb filter or notch Y/C separator, convergence adjustments in the form of rings around the picture tube neck, or pots, usually with fewer than 16 points, zoom or aspect ratio changing accomplished by spreading out the scan lines.

These are digital features of a TV (not always present): Line doubler (de-interlacer), 3 line adaptive comb filter, 3D comb filter, LCD/plasma/DLP/DILA display or projection panels, circuits to drive the former, HDTV tuner, Firewire(tm) input, DVI input, convergence adjustments in the form of button pushing on your remote and generally with more than 40 points, zoom or aspect ratio changing accomplished by formatting the picture onto a different number of scan lines (scaling).

I am not sure about picture-in-picture, I think that uses digital processing.

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We do not have experience with many specific makes and models of TV sets and other equipment and therefore cannot give you any recommendations on what to buy. While you may find useful hints on this and other web sites, we still recommend going through checklists that Consumer Reports magazine publishes from time to time.