Originally Posted by Chronoptimist
Personally I would rather be slightly cooler than quite a bit warmer than intended, if I couldn't do anything to further calibrate the screen.
Agree with this.
This is undoubtedly covered in more detail in the calibration FAQ, but if you want accurate color on your display, there are (at least*
) four pieces of criteria that really need to be satisfied.Color Gamut & Primaries
First, the physical colors of the red, green and blue sub-pixels on the display need to be the right colors to comply with the HDTV spec. In calibration parlance the individual colors are referred to as "primaries
". Together they make up the display's "gamut
", which represents all colors the display can produce. A popular trend on newer TVs is the so-called "wide gamut", which implies the display exceeds the gamut needed to meet the HDTV spec. This has upsides and downsides. On the one hand, it can make colors on the display appear more vibrant and saturated. The tradeoff is that the colors may not be as accurate or true to the artistic intent of the video's creators (assuming the content was mastered on a display with correct HDTV primaries). Some wide gamut TVs will allow you to switch between a "normal" and wide mode though. Usually the normal setting will be closest to the HDTV spec.Color Temperature & Gray/White Balance
The second piece in the puzzle is the brightness of the red, green and blue primaries relative to one another. This determines the specific color or "temperature" of the neutral (ie gray and white) color tones on the TV, hence the terms "white balance", "white point
", "grayscale", "gray balance", etc., which are used more or less interchangeably in video (though they may have subtle distinctions). IMO, terms like "white balance" are a little misleading because the particular blend of red, green and blue needs to be the same for all
levels of gray on the display, going from black (really dark gray) through white. All levels of gray on the TV should be adjusted close to standard illuminant D65
, which is one of many colors with a temperature
of ~6500 degrees on the Kelvin scale. Most displays unfortunately do not meet this criteria, and will also gradually change in color as they transition from darker to lighter shades of gray.
There are different ways of handling temperature/grayscale adjustment depending on the type of controls on the TV. If there are two or more points of control for the levels of each primary, then it should be possible to adjust gray balance pretty close to D65 for most of the range of grays on the TV using a colorimeter (or possibly an optical comparator, if you have very good eyes and alot of patience
). If the display only has a single control for each primary level, or a simple temperature adjustment, then it's usually preferable to err towards the "cooler"/bluer side as Chronoptimist mentioned above (that's "cooler" in subjective terms, not in kelvins). If the whites on the display appear cooler than the dark grays for example, then it's usually preferable to adjust the darker grays close to D65 and let the lighter grays "go blue". Some people will split the difference though, and adjust the midtones closest to D65.Saturation, Hue/Tint & Color Decoding
The third link in the color chain is how well the TV internally translates color from a video source to pixels on the screen. This is often referred to as "color decoding". Most TVs will have two adjustments for this in their basic user controls, usually labeled "Color" (short for color saturation), and "Hue" or "Tint". Some TVs may have additional color decoding adjustments in their advanced and service mode settings. On most newer TVs, all you generally need are the basic user controls because internal color decoding errors are not as common on the newer technologies as on tube/CRT-based TVs. Some red or green "push" may still exist though on certain brands/models. (Panasonic is known for pushing some green on their TVs for example. And most of Sony's older HD CRTs had a prominent red push, which can be corrected in the service mode).
To accurately adjust the Color and Hue/Tint controls (w/o a meter), you need some way to isolate the red, green, and blue primaries on the TV, so you can look at each independently with a color pattern. Some TVs will have a "blue mode", and sometimes also red, and green modes to facilitate this. These would typically be in the advanced or service mode adjustments. If your TV doesn't have these controls, another option is a set of color filters, like the ones included with some calibration discs, or the blue glasses from THX. The filters aren't quite as the accurate as the isolation modes offered on some TVs, but in many cases they're the only option aside from a more costly color meter. FWIW, I've posted some tips on how to get more reliable results from the Digital Video Essentials color filters (SD Component edition) in the following links...http://www.avsforum.com/avs-vb/showt...9#post19000189http://www.avsforum.com/avs-vb/showthread.php?t=1271276
Misadjustment in the Hue/Tint control is also not as common on newer TVs as it used to be, so it's frequently best to leave that control either at the middle or default setting, and make adjustments with only the Color control. If you can't get color decoding patterns to appear correct with just the Color control, then a slight Hue/Tint adjustment might be warranted. Before you do that though, I'd recommend looking at tips in the links above, especially if you're using filters. Some video players/STBs may also exhibit color decoding/saturation errors, so it's a good idea to check with other users of your video input devices to see if they've encountered similar issues, if you're having trouble getting decoding patterns correct on your display.Ambient Color Temperature/Room Lighting
The first three components above are all "device-related" issues/criteria. For correct perception of color on your TV though, there's another factor to consider which is the viewing environment around the TV. As mentioned in a post above, the color of the room lighting (and also walls and furnishings to a degree) can influence your perception of color on the display. For video mastering, SMPTE recommends ambient light close to the white point of the display (D65), and neutral gray surroundings. Assuming these guidelines are followed by video producers, the closer the illumination around your display is to D65 (or daylight in general which runs from about 5000K to 6500K), the more correct the colors should appear. Many people (including yours truly
) find lighting in the 6500K range a bit harsh on the eyes for nighttime viewing though.
Unfortunately, there's no practical way at the moment to adjust the color on a display to appear perceptually correct in other kinds of room lighting (such as the 3000K illumination that's typical in most homes). This may be possible in the future however as color appearance models become more robust. In the meantime, some compromise may be necessary for users of direct-view displays who prefer warmer room lighting, but still want reasonably accurate color. My solution is to use a subtle
daylight fill (or "bias light") behind the TV, and regular incandescent lamps in the rest of the room. Another possible solution is to use room lighting more in the 4000K to 5000K range (iow, something cooler in appearance than 3000K, but not as harsh as 6500K). FYI, the recommended ambient temperature for computer and web apps is 5000K (D50), which might be worth considering as well.
I mention these other factors to illustrate that there's more to acheiving accurate color than just getting the temperature/gray balance correct on the display; and to point out that if you tinker with only one component in the scheme without considering the others, you may not really be "improving" the color on the display.*
What's not covered here is gamma, black and white level adjustment, and ambient/surround levels, which have more to do with the contrast/brightness of the image, but are also intertwined with color issues in some ways as well.