Why are colors reproduced differently between devices?

Let’s take a look at the four photos shown below. Each of the photos is shown on four different screen monitors. Note how different the colors look on the monitors. Before color management is implemented on the four devices, there are visible color differences due to varying hardware technologies and color settings. The default color settings, for example, color temperature, saturation and contrast, you find on your home’s display will generally cater to the color needs of typical use. However, for commercial printing companies and for freelancers and professionals whose work requires color precision, color management becomes essential in their workflow.

LCD monitors of the same model will also exhibit color mismatch due to deviations in backlight modules and color filters. Calibration can reduce the color differences between displays.

Below are devices that use different color systems to produce color. Optical devices use additive color mixing while print devices use subtractive color mixing.

1. Optical input devices: cameras, scanners
2. Optical output devices: monitor displays, projectors
3. Print device: printers

Additive Color

Additive color theory states that colors are produced by mixing light, specifically red, green and blue light. These three colors are called the primary colors for additive color model. Other colors can be produced by mixing various amounts of red, green and blue light to create secondary colors: cyan, magenta, and yellow. Mixing red and green light gives you yellow light. The overlap of green and blue produces cyan. By combining blue light and red light, magenta is produced. When all three primary colors are added together, white light is created.

The commonly used RGB color space uses the additive color model where red, green and blue light are mixed in various amounts to create a broad range of colors.

Subtractive Color

In the subtractive color system, colors are produced by mixing colorants. Certain colors of light are absorbed (subtracted) by the colorants whereas others are reflected and seen by the viewer. The subtractive primary colors are cyan (C), magenta (M), and yellow (Y). If we mixed yellow and cyan, we would get green; mixing yellow and magenta gives us red; and combining magenta and cyan produces blue. Theoretically, the combination of all three primary colors would give us black; however, in reality, a dark brown results. Hence, a fourth color, black (K), is added to color printing to compensate for the imperfect color produced from the primary color trio.

This subtractive color model is referred as the CMYK color space comprising of cyan (C), magenta (M), yellow (Y) and black (K).

What is Color Management?

Color management is the process by which color standards and hardware/software calibration devices are used to reduce the color differences among devices so colors are reproduced accurately.

The benefits of color management:

• Colors on the monitor reflect the colors that are similar to the colors in real world
• Monitor accurately displays all the necessary details
• Allows authors to effectively communicate the right colors with the audience
• International standards allow effective communication with customers, suppliers and employees

3Cs of Color Management

1. Calibration

   Calibrating a device involves adjusting display properties (e.g. brightness, black level, white point, gamma) to a standardized value so there is conformity between devices.
   
   

2. Characterization

   Characterization refers to the profiling process. Each device has a characteristic color response which is measured with a color measuring device and recorded in ICC profile.
   
   

3. Conversion

   Conversion translates color from the original device’s ICC profile to the target device’s ICC profile.

There are two methods of calibration: software calibration and hardware calibration.

1. Software calibration

•  Advantages
  Software calibration is a common calibration method used by typical monitors on the market. An ICC profile is generated and the monitor’s color data is modified by altering the values such as white point, brightness and gamma in the video card’s look up table (LUT).
  
  
•  Disadvantages
  Software calibration requires manual adjustments of color settings, hence problems with precision can occur. Since there are several settings that need adjusting, it may take some time to familiarize with how the calibration works. The biggest downside to software calibration is that slight banding and gradation damage can occur.
  
  

2. Hardware Calibration

•  Advantages
  Hardware calibration is easy to set up and can be completed within a short period of time. Adjustments are made directly to the monitor’s hardware LUT so colors reproduced have high accuracy and smooth gradient transitions. Since hardware calibration is an automatic process, repeating this procedure would render precise results every time, whereas software calibration would produce slight minor differences each time the process is conducted.
  
  
•  Disadvantages
  Monitors offering hardware calibration are often priced higher than standard monitors without hardware calibration.

Calibration devices and calibration software accomplish the first two steps of the 3C calibration procedure: calibration and characterization. This creates a profile that is used in the conversion step, enabling monitors with hardware calibration capability to correctly display the recalculated color values.