Notes on screen calibration

Definition of screen calibration

In the past, many people said that to calibrate the screen (Calibration) is to adjust the screen to seem to be printed. The general method is to use a printed manuscript as a benchmark, and then use some software such as Gamma provided by Adobe or directly use The adjustment function on the monitor to achieve the color similar to or the same as the printed matter. But this is a way of not having an ICC workflow in the past. This way can only achieve its own purpose of drafting, and it may not be the same result for every software. There is no centrally controlled part to unify colors, so Apple developed a system extension program called ColorSYnc a few years ago. This is to use the system software's ability to process colors centrally, but the central controller needs some data on the color characteristics of different devices. These data are called ICCProfiles, and the production of these ICCProfiles requires appropriate hardware and software.

The first task of screen calibration

We can divide the screen calibration into two parts. The first is the environment control. Although the screen is a transmissive display, the surface of the screen picture tube will also be affected by the surrounding light, for example, when the light directly hits the screen The contrast of the image will decrease in real time. The reason is that the light in the room is reflected on the glass of the kinescope, so that the black part cannot produce enough black. If the indoor lighting is turned off, the contrast on the screen will suddenly increase, but I believe no one likes to work in a completely dark environment, which makes the workers feel uncomfortable. A better method is to properly control the indoor lighting so that the light cannot directly hit the tube glass. A very effective method is to add a light blocking part to the screen.

Stable and standard lighting

Just said that properly controlling the indoor light makes the contrast of the screen have good results, but many friends will ignore the lighting of the original. When we control the light to not illuminate the screen, the lighting on both sides of the screen is insufficient, and the color temperature Not allowed, so it is best to have a stable and standard reading light box. The light box is usually designed with precision, and is generally an international standard with a color temperature of 5000K. The angle of light reflection does not cause reflection, and the lighting is average.

Color Temperature

Color temperature is used to refer to the degree to which the light color is relatively white to quantify the light color performance of the light source. According to scientific theory, heating a standard black body with complete absorption and radiation capabilities, the temperature gradually increases and the color changes accordingly; the temperature at which the black body heats up to a color close to the light source is defined as the relative color temperature of the light source , Referred to as color temperature, for the absolute temperature K (Kelvin, or Kelvin) as the unit.

The more bluish the light color, the higher the color temperature; if it is red, the lower the color temperature. The light color during the day also changes with time; the light color is yellowish at 40 minutes after sunrise, and the color temperature is 3000K; the noon sunshine is white and snowy, rising to 4800 ~ 5800K, and about 6500K at noon on cloudy days; The color temperature dropped to about 2200K again. For artificial light sources, there are tungsten filament light bulbs 2000 ~ 3400K, generally beige light tubes 2600 ~ 4000K, generally white light tubes 6000 ~ 8000K, and we design and print industry need 5000K standard color light tubes.

Why have standard shades! Because of 5000K color temperature light source.

(1) In the middle of the visible spectrum,

(2) It is white light with balanced color,

(3) No emphasis on any color,

(4) Internationally recognized standards.

It is difficult to reproduce all colors on a computer screen. Everyone understands that it is actually impossible to display the image on paper on the screen without deviation, because the colors on the screen and the paper are completely different. Physical phenomenon.

Screen calibration and characterization

It is difficult to reproduce all colors on a computer screen. Everyone understands that it is actually impossible to display the image on paper on the screen without deviation, because the colors on the screen and the paper are completely different. Physical phenomenon. The color display of different brands of screens can be very different, and the temperature of the screen is another factor; the color of the display may be different after the same screen is turned on for several hours, and the aging of the hardware also affects the stability of the color display; the screen Phosphorus will decline with time. Finally, the external light sources of your work environment will also work, because when they are projected on the screen, they will mix with the colors emitted by the screen.

The color temperature of the white point of the unadjusted screen is higher, and the color temperature is between 8000 and 9500K, which is obviously blue. In order to make the color between the screen and the finished product or printed product have a close effect, you should set the white point of your screen (WhitePoint) to the color temperature of the indoor bulb when you look at the color. And set the appropriate gamma value (Gamma) purpose is to adjust the contrast displayed on the screen to be consistent with the drafting or printing. The working steps of screen calibration are as follows:

(1) Fix the light at the working position first, or have a standard color light box for color matching.

(2) Start the screen and warm up for at least 30 minutes, so that the picture tube of the screen reaches a stable state.

(3) Turn off the desktop pattern, and change the background of the screen to medium gray, so as to avoid the interference of the background color.

(4) Start the screen calibration software.

(5) Follow the software instructions to adjust the light and darkness and contrast of the screen, use tape to press the system or lock it with the software.

(6) Select the white bit color temperature and contrast value, usually the requirements for printing WhitePoint is 5000K and Gamma is 1.8.

(7) Hold the colorimeter or spectrophotometer at the specified position on the screen.

(8) Follow up and store the measured data and ICCProfile.

The above are the steps for general screen calibration. The following explains the actual working situation. First, use AppleClolrSync's DefaultCalibrator, which is a free and simple screen calibration tool that helps you to calibrate the gamma and white point of the screen. The method of use is very simple, as long as you follow the instructions of the software, because the single * eye observation to correct, the accuracy will be poor, if you want more accurate screen calibration, you may need some equipment, these equipment include colorimeter, It uses an instrument attached to the screen to measure the color of the light emitted by the screen. The screen calibration software commands different colors on the screen. The color emitted by the color measurement screen is sent back to the computer, and the actual measured color is compared with the color that should display the ideal color, so that you can adjust the color temperature and gamma settings to obtain a certain set of goals.

Finally, how to verify whether the color and darkness of the screen display are appropriate, teach you a simple method, open a blank window on the screen, then put a piece of white paper under the color light source, and then use a card to open two Use a card to observe the color and darkness of the two holes. If the color temperature is not correct, you can pull the color temperature control in the software to correct it. If the darkness is not correct, you must change the intensity of the light source, so you need to have adjustable light and dark The light box is easier to get the desired effect. If you want a more accurate reading, you can use the easy-to-use key-type light meter to measure the white level on the screen and see if the white paper reading under the color light source is consistent, and the color temperature can be measured with a color temperature meter.

Finally, let ’s remind you that if you have a special program for screen calibration on your system, you ca n’t use other calibration software such as AdobeGamma or AppleClolrSyncDefaultCalibrator at the same time.

After the screen calibration is completed, it is only necessary to re-calibrate it when the conditions change, or if its luminous body "drift" changes, it is proposed to re-calibrate once a month. A good way is to fix the brightness and contrast adjustment device of your screen with adhesive tape after the calibration is completed, and keep the lighting conditions unchanged.

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