A Discussion on ISF Calibration
First of all I would like to thank the HighDefForum member d6500k who is an ISF technician in the development of this essay. I contacted him to fill in some blanks I had to generate this essay. It turned out he filled in a lot of blanks and in fact ended up responsible for a great deal of this information and confirmation of the material. We e-mailed back and forth over a couple of weeks, so his time is much appreciated. His input has been most valuable and hopefully he will monitor the thread for follow-up. Thanks d6500k. Visit his Website: www.6500kcalibrations.com
- Front panel control adjustments
- Brightness and contrast: Two of the most important controls that ultimately determine the displays capability. These adjustments will interact with each other to some degree in almost all types of displays. Brightness will affect the black levels and the contrast or picture control will affect the peak white level. On CRTs, issues such as blooming and line distortion can occur with these adjustments and the tech will alternately adjust both until the best average is found for each. Digital displays require precise adjustment as well. White/black clipping occurs on almost all light engine devices causing bright areas to merge, defeating definition. Black levels are getting better with each iteration, actually making this control more important to set correctly.
- Color and tint - These adjustments are made after placing the blue color bars test pattern on the display and using the blue filter. Matching the blue bars top and bottom while using the color/hue (tint) controls will render a correct setting if the color decoders are also correct. These controls also interact to a degree so care must be taken. Red and green filters allow the accuracy of the decoder to be accessed with another decoder error test pattern. Final adjustments are usually a best average if color decoder manipulation is not possible. Many TVâ€™s are designed with the red being overemphasized and sometimes it is necessary to reduce overall color saturation to get decent red levels slightly de-saturating greens and blues.
- Sharpness - This is really an edge enhancement control and should be defeated for film viewing from a quality source. Assuming your set is fairly recent, this adjustment may not have much affect. Test patterns confirm proper settings, which may need to be accessed in a service menu.
- Service menu adjustments.
- Grayscale - SMPTE-C phosphors for broadcast use is the ideal, but many manufacturers will use whatever phosphors they can get readily. This will cause color variance from brand to brand and even from model to model. Grayscale is an adjustment that is not generally available from the front panel control adjustments. It is one of the most important adjustments the ISF tech will make. The NTSC decided way back that the correct shade of white from very dark to very bright in video systems is 6500 K (kelvins) which is about like midday sunlight. Since all of the studio monitors which are used as reference when the video source was created are calibrated to 6500 K, if your TV does not match 6500 K, every color will be different than what the creator intended. For example, 2800 K is labeled as being warmer or redder white. If your TV were less than 6500 K, every color would be biased toward a reddish tint. If higher than 6500 K, a cooler bias will occur tending to be blue. Many displays “out of the box” will have color temperatures upwards of 10,000 K. Manufacturers set them up this way to “stand out” on crowded showroom floors.
- Overscan: Analog and Digital displays handle overscan differently. Overscan is/was necessary with analog displays to “clean up” transmission anomalies such as the blanking intervals on the top and bottom of a picture. NTSC actually transmits 525 lines of information of which you see 480. The 45 lines not seen carry the information that among other things, controls the stability of the transmitted picture. The width of overscan is to alleviate underscan which shows ragged edges when the limits of the raster are reached. Typically 4 to 5% overscan can be achieved by the ISF controlling parameters in the service menus of analog displays. Digital displays use the same controls but in a slightly different way. Again ISF controls the “size” through the service menu settings that allows the display to show all data possible leaving the edges “hidden” so you donâ€™t see bars on the tops and sides of your screen. With the exception of some front projectors and some other fixed pixel displays (plasma, LCD, etc.) that are used with external scalers, all signals are routed through the internal scaler, so matching the input signal to the nearest native set resolution may not be necessary. An ISF tech will evaluate which format your STB matches up best.
- Data Paths - If the video signal is being sent through a pre amp processor or a receiver, the ISF tech will check via resolution charts whether all of the possible signal is being passed. In many cases, but not always, bypassing receivers or preamplifiers/processors in favor of a direct link via DVI or HDMI connections between the display and source, to potentially provide a better picture.
That pretty much is the standard ISF calibration service. There are services that can go beyond the basic calibration if the set should need it and with analog displays are considered standard as well. Some such adjustments would be the displays geometry and convergence. CRT sets require adjustments of this type. Pincushion, trapezoid, tilt, rotation and others are common adjustments that are normally factory set to acceptable parameters. Precise alignment of the RGB CRTâ€™s may well produce the most “bang for your buck” with regards to overall picture clarity. Fixed pixel displays generally have few electronic adjustments available to a tech other than size controls. Some manual manipulation of the light engines themselves may help geometrical distortions.
Screen Protector removal - Some RPTVs have a semi-clear finger guard that introduces glare into the set. Some are not removable which can be a problem if the display is not in a light controlled environment. These “shields” are to defray the potential damage to the lenticular screen in front of the Fresnel lens. Normally made of thin plastic, these lenses can be marred or damaged easily thus the need for some protection. When the display in within reach of “SUPâ€™s” â€“small unpredictable people- the protective shield is a good idea. When possible, it is better to remove or restack the shield. By doing so the display will not produce reflections to the same degree as when the shield is in place. The resulting appearance after removal will be enhanced by the limited reflections and to a much lesser degree, the display will be brighter when the shield is removed entirely.
Removal and/or restacking can be initiated by researching the web for your type of display. Then simply follow the directions from service manuals. The task varies from a 15 min. job, to over a few hours. Take extreme care with the lensâ€™s as they are very fragile. Two people make this task much simpler.
The Imaging Science Foundation, Inc (ISF) has a certification for HDTV sets called the Certified Calibration Controls or CCC. This has not been widely accepted by all manufacturers yet. It is intended to allow the setting of certain parameters which eliminates the need of accessing the service menus, which ISF believes should be reserved for factory adjustment only. The CCC adjustments are provided for two sets of non-volatile presets one for ISF Day and the other for ISF Night modes. ISF recommends, but does not require, a timed switch between modes.
The settings that ISF requires as the basic parameters in each CCC adjustment are:
- Sizing and centering
- Sub-adjustments for Front Panel controls
- Color balance
- Convergence, if applicable
- Primary color and decoder optimization, if available
- Anti-Burn features, if available
If the HDTV set is not certified by ISF with the CCC certification, then the only option the ISF technician has is to go into the service menus and set the necessary parameters.
Many adjustments can be user performed by use of a calibration disc like the Digital Video Essentials or The AVIA Guide to Home Theater DVDs.
Here are some do it yourself DVDs.