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Calibrations and Maintenance
Setting Up and Maintaining Your Home Theater
The work (hopefully it's fun!) shouldn't end after you have selected and installed your home theater. While we hope you are seeing and hearing everything you have hoped for, the system should still be optimized to deliver all its potential performance. This optimization is frequently referred to as a calibration, and consists of setting up the display's adjustments with your actual sources to get the best pictures. You can do this yourself, but you would likely get the best results from using a professional calibrator, who will usually have special signal generators and light measuring equipment, as well as the knowledge to use them.
A calibration consists of making all the basic adjustments to achieve optimum performance in a specific installation. This includes performing mechanical adjustments, such as focus in front projection systems, evaluating the basic out-of-the-box settings, which may be optimized for the dealers showroom and not a home theater environment, and making adjustments for the specific sources to be used. While the professional calibrator will likely be faster and more thorough, you should be at least aware of what is involved, what is being done, and why it is being done. We'll go over a few of the basic adjustments here, and you'll be able to find more information in the
Display Performance section of WalVisions. Note that higher performance CRT projectors have a more involved setup that is beyond the scope of this discussion, here we are more focused on the more common lamp based, digital projectors.
The initial setup should include careful display alignment and positioning. While this is primarily an issue for front projection, for which the screen usually is first mounted and then the projector is then aligned, self contained displays should be positioned and angled for comfortable viewing. When choosing the location for the screen or display, be wary of stray light sources such as windows, doorways, room lights, etc. Try to avoid having lighting from these sources falling directly on the display, or from distracting from the display by being behind. The display should be located at approximately eye level, or even a little lower - unfortunately the over the fireplace mantle mounting for plasmas is
far too common, as looking up at the display can be fatiguing. The viewers should sit more or less in front of the display, and not way off to the sides. For front projectors, try to avoid using the electronic keystone correction, and use lens shift instead, which will keep optimum geometry without loosing resolution.
To make the electronic adjustments you will need test patterns, and the best way to get these is by purchasing one of the DVD based alignment discs, such as Avia Guide to Home Theater, Digital Video Essentials, or Sound and Visions Home Theater Tune-Up. These discs come with patterns and instructions, and also include sound systems tests. DVDs with THX movies also have test patterns included. While we think that the patterns
here at WalVisions can be of great help in educating and evaluating your system, a true and critical calibration needs to be done with the actual sources to be used, such as the DVD. Thus you can use the
WalVisions patterns to check display performance and to calibrate your display for the PC source, but not necessarily to calibrate it for the other sources.
The basic calibration should consist of
adjustments to focus, geometry, image centering, color temperature, brightness (black level), contrast (white level), gamma, color, tint and sharpness. Here are a few general comments regarding these steps - you can find more detailed information about these subject in Light Levels, Contrast, Gamma and in Display Performance. Note that this is not a procedure, just some general guidelines that we hope will help accustom you to what might typically be done in a calibration. If you ever do make adjustments, however, we highly recommend writing down any current menu settings before making changes - then if making the change(s) doesn't
yield the expected results, simply return the setting(s) to the original value(s).
Focus: For the most part, this applies to front projection only, where the lens must be adjusted for optimum focus for all colors over the entire screen. Use a full field focus, dot or crosshatch pattern, and set the lens focus for the best overall focus. Stress the center areas, but check all colors in all parts of the screen to find the best overall focus.
Geometry and Centering: Geometry adjustments basically
correct the size and shape of the image. For front projectors, adjust the zoom for an "overscan" (how much the image edges extend beyond the viewing area) of about .5 inch per edge. Select the aspect ratio that is appropriate for the display and source, which will usually be 16:9, widescreen, for both. Select the electronic overscan, if available, to view the maximum image detail without viewable edge effects. If there is an available adjustment, center the image about the display area using the centering controls.
Color Temperature: Check and adjust the so the various levels of gray are colorless. This is almost always best done by meter, but
under the right conditions the eye can be a pretty good judge too. The simplest method, if it is available via a menu item, is to select "6500" as the color temperature, and hopefully the factory setup will be accurate. The best way is to use a light meter and appropriate window test patterns to adjust the red, green and blue menu items to achieve the correct meter readings. The intermediate method is to use your eye to make the adjustments, without a meter, but be careful when judging by eye, as the eye is affected by what has been
recently viewed. If possible and it's daytime, simply go outside and look around to get the eyes neutralized, then come in and
evaluate, and make adjustments as necessary, while letting you
eye be the judge of what is a natural, "colorless", white.
Always adjust the color temperature with signals/patterns that
are truly "black and white", or, if possible with the controls
in the display, adjust the Color control to zero to eliminate
all color present in the video signal.
Brightness (Black Level):
The brightness adjustment usually varies the luminance of all
image areas, dim and bright, and is set so that the black levels
in the image just match the black level of the display. It the
brightness to adjusted too high, the image will appear washed
out with extra light, similar to someone shining a light on the
screen. If the brightness is adjusted too low, some of the
details in the darkest parts of the image may not be visible.
Usually this adjustment is made with a "pluge" pattern, or some
pattern that has a lot of "black" and some areas that are just
above black, and the adjustment is made so all the areas just
above black can just barely be seen, but the truly black areas
are are at "display black" - the minimum level possible with the
display.
Contrast (White Level): The contrast adjustment is
usually an adjustment that doesn't affect the darkest areas of the image, but causes the brighter and white areas to lighten or darken. Normally the contrast adjusted as high as possible before negative effects occur. For CRTs the negative effects are
the "blooming" of white details and possibly picture bending and size changes. For lamp based projectors, the negative effects are a loss of detail in the whitest areas, or a change of color in the whitest areas. Note that for lamp based projectors, since the black level is a fixed amount set by light "leakage", you will only get the best contrast
ratio if the contrast adjustment to set to the maximum possible before the negative effects are seen.
Gamma: The gamma function determines how the brightness levels between black and white are displayed. To make these levels display correctly (with the correct intensity), a gamma of
2.0 to 2.5 is usually appropriate, but this will depend upon the display device and the viewing environment.
The higher gamma values are best for high contrast displays in a
dark environment, while the lower gamma settings are appropriate
for lower contrast displays and/or displays viewed in a
moderately well lighted area.
Color and Tint: These controls are
hold-overs from the NTSC system, and set the color intensity
(saturation) and color shading (hue) in the image. Composite, S-Video and component video signals all have a "luma" (luminance), or black and white part, and then a "color difference" part that is added to the luminance to recreate the true red, green and blue signals. Since these colors are all created starting with the luminance, they will only be correct if the luminance "color temperature" has been set correctly. Correctly setting the color and tint adjustments is fairly simple by using the patterns and viewing color filter that comes with the test DVDs. Note that ideally these adjustments are not needed for today's component video sources, as the colors should come out perfectly - but sometimes these adjustments can compensate for errors either in the display or the source.
Sharpness:
The sharpnes (sometimes called detail
or edge enhancement) adjustment can make the image appear "sharper", but should be used with caution as
frequently the apparent detail is really a distortion of the image.
Adjust for a natural looking image, being careful not to create
artificially "hard" edges to objects in the image.
Maintenance:
Now we have just a few words about maintenance, both from performance and reliability viewpoints. After initial setup and calibration your new display should look top notch - remember this performance level, and be ready tweak the system as necessary to maintain that performance level. Once you have a good understanding what the various adjustments do, and just what a good image should look like, keeping your display well adjusted should be routine, and you will then maximize your entertainment satisfaction.
With virtually all lamp projectors, the only normally required maintenance consists of periodic filter cleaning, as well as occasional lamp replacements. We strongly encourage you to keep the filters clean; excessive heat is the enemy of
electronics and lamps. |
