Background

Mobile Display Technology ~ Color Theory

All mobile devices are direct view devices that are flat-panel, according to Louis Silverstein, who wrote Color Display Technology: From Pixels to Perception in 2006. He also states that one of the most active application markets driving advances to enhance color performance and improved image quality is the small, high-performance color displays for mobile devices. Combining successful technologies or creating new innovations has lead to many different display technologies with significantly different color characteristics to provide manufacturers with more competitive display solutions to provide a more positive user experience (Safaee-Rad, 2012). These technologies include:

• Thin Film Transistor (TFT ) LCDs are the most common type of display units used across mobile phones. TFT LCD offer better image quality and higher resolutions compared to earlier generation LCD displays but their limitation lies in narrow viewing angles and poor visibility in direct light or sunlight (Nairaland, 2012). Pros - most mature technology with excellent color. Cons - not power efficient, poor outdoor readability (Huang, 2010).

• In-Place Switching  (IPS) LCDs are superior to normal TFT LCD displays with wider viewing angles and lower power consumption, which leads to a much improved battery life. IPS-LCDs are costlier than normal TFT LCD and hence are found only on higher end smart phones (Nairaland, 2012).

• Super Liquid Crystal Display (S-LCD) differs from a regular LCD in that it does not have an air gap between the outer glass and the display element and makes the user feel "closer" to the display (What is Super LCD?, n.d.).

• Organic Light Emitting Diode (OLED) is a display technology based on LED which uses a thin film of organic compound as its emissive layer (Huang, 2010). OLED is much better compared to LCDs because of their exceptional color reproduction, blazing fast response times, wider viewing angles, higher brightness and extremely light weight designs (Nairaland, 2012).

• Active-Matrix Organic Light-Emitting Diode (AMOLED) displays have all the attributes of an OLED display like brilliant color reproduction, light weight, better battery life, higher brightness and sharpness and light weight designs.

• SUPER AMOLED or Active Matrix OLED, is a hybrid display technology that allows faster pixel switching response times (What is Super LCD?, n.d.).

• Retina Display is a term used by Apple for its high resolution (640 x 960 pixels) IPS LCD (with backlit LED) used by them in iPhone 4 and 5. Retina display is named relates to its pixels cannot be individually identified by the human eye, thus making the display super sharp and brilliant (Nairaland, 2012).

• High Definition (HD) standards are 720 pixels HD &1080 pixels for FULL HD LCD.

• HD+ 720 pixels, which is 7% more pixels than HD (Nokia, n.d.).

 



(Bleicher, S., 2012)

Color Theory

Three essentials needed to produce color: Light source, an object, and an observer.  It is light that has been modified by an object in such a manner that the viewer—such as the human visual system—perceives the modified light as a distinct color (X-Rite, Inc., 2004). Light is the part of the electromagnetic spectrum and is transformed into colors through wavelengths. Objects can reflect and transmit light, but this study focuses on the emissive light source of the mobile device displays. They have their own unique wavelength composition. This arrangement of wavelengths that leave the object is called spectral data or reflectance intensity and is measured with a spectrophotometer (X-Rite, Inc., 2004). The resulting measurement is the most accurate of the object’s actual color.

In 1931, the CIE established a color model that represents the visible spectrum based on the visual capabilities of a Standard Observer, a hypothetical viewer and common light sources. Using this model, we can compare the varying color spaces of different viewers and devices against repeatable standards. These two variables allow device- and illuminant-dependence. This model was limiting its chromatic definition. The new approach involved an opponent theory of color vision, which states that two colors cannot be both green and red at the same time, or blue and yellow at the same time (X-Rite, Inc., 2007). As a result, single values can be used to describe the opponent attributes.
This approach was named the CIE 1976 L*a*b* color model and is presently one of the most popular spaces for measuring object color and is widely used in virtually all fields (Konica Minolta, 2003). The L* defines lightness or the gray-scale component of the color, a* denotes the red/green value and b* the yellow/blue value. Spectral data measures the composition of light reflected from an object before a view or device interpreted the color (X-Rite, Inc., 2004).

The assessment of color is usually an assessment of the difference or delta from a known standard. The CIE L*a*b* model illustrates the distance of the compared colors on the model diagram. The expressions for these coordinate color differences are:

• ∆L* - the lightness difference
• ∆a* - red/green difference
• ∆b* - yellow/blue difference (Datacolor, 2009)

Given coordinate values, the total difference or distance on the CIE L*a*b* diagram can be stated as a single value known as Delta E (∆E). ∆Eab = [(∆L2 )+( ∆a2 )+( ∆b2 )]½ (X-Rite, Inc., 2007).