Every monitor displays color differently than every other monitor. This is true even for brand new monitors made side by side at the factory. None of these monitors will display color that will match the color from you output device. Why this is and what you can do about it is what will be discussed here.
Brand new monitors have a natural blue-ish tint right out of the box. This tint (or cast) will probably look natural to you because your eyes will naturally adapt to make the lightest area look white. Even so, the color white that you see on your monitor and the displayed reflected white from your printed output probably don't match. This means that the image you work on and correct on your monitor will look different when printed out. Calibrating your monitor and utilizing a profile of the monitor along with a profile for your output device will ensure that what you see is what you get.
To have a common point of reference when talking about color and in particular the color of white, color scientists have defined a scale for color measurement to quantify the color characteristics of light. This scale if often referred to as color temperature and is measured in degrees Kelvin (K). If you were to measure the Kelvin color temperature of your new monitor you would probably find it set around 9300K. This color temperature is considered a very blue-white. The color temperature of light used to illuminate it defines the color temperature of a printed output. Daylight is considered to be neutral illuminant at around 6300K. A color temperature of 6300K is much less blue than 9300K. The standard color temperature of light tables and color booths for the photographic industry is 5000K. This color temperature will actually look yellow in comparison to a 9300K-color temperature source. This is the main reason your printout does not match the way it looked on your monitor.
Another characteristic of color is Gamma. Gamma is use to describe the transition of brightness from white to black. Gamma can range from 1.0 to 3.0 but has a useful range of 1.8 to 2.2. The higher the Gamma value for a device, the darker the midpoint color (and conversely for a lower Gamma). Gamma for a Cathode-Ray-Tube (CRT) monitor is usually 2.5 but this will differ from tube to tube and over time. It will also change from with each system (Mac, SGI, and PC) the monitor is attached to and what video card is used. Therefore, the only way to determine the actual Gamma is to measure it.
Now that we know a bit more about monitor color and how it can change, lets look at why you need to calibrate your monitor. With all the variances in monitor color and how they can change over time, the only way to ensure a consistent, repeatable output is to constantly check the monitor correct color calibration. By constantly re-calibrating your monitor, you will be brining it back to a known standard.
I use OptiCal by Color Vision to calibrate my monitor about once a week. It is a simple yet powerful device that attaches to the monitor screen and sets the white point, black point, color balance, and gamma. It is a very useful tool because it takes the objectivity out of the calibration. What looks good to me might not look good to someone else. It also helps in matching my printer output to the colors I see on the screen.
At a minimum you should always try to at least have the contrast and brightness adjusted correctly. Click here to find a gray scale and instructions for making these adjustments.
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