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Display Design and the Human Vision System

PenTile® technology is biomimetic, meaning it is designed to compliment the complex mechanics of the eye-brain system. As a simple example of eye mechanics consider how the eye utilizes the color blue. The eye has cone receptors that sense color and brightness, and discern patterns. These cones are sensitive to different wavelengths of color—primarily red, green, and blue. The blue cones detect mostly color (chroma) information, while the red and green cones do most of the work resolving images by discerning luminance, edges, and structural details of images, as well as contributing to color vision. The red and green cones are used independently, each cone seeing a "dot" of black and white—ignoring its color to produce high resolution luminance perception—and are used in opposition, comparing the amount of red versus green, to produce low resolution color perception.

The PenTile RGBW™ layout uses each red, green, blue and white subpixel to present high-resolution luminance information to the red and green cones, while using the combined effect of all the color subpixels to present lower-resolution chroma (color) information to all three cone types. Combined, this optimizes the match of display technology to the biological mechanisms of human vision.

Other human-vision factors such as the logarithmic representation of luminance values, variable resolution between the center and edge of vision, and the separation and compression of brightness and color differences are also exploited in the design of PenTile RGBW™ displays.

How are images rendered on a PenTile RGBW™ display?

The same image data drives both RGB stripe and PenTile RGBW™ displays. However, conventional RGB stripe displays render (draw) images by assigning a color and luminance (brightness) to an entire RGB-triplet as a whole pixel, adjusting its three RGB subpixels to set a single addressable point.

Images on a PenTile RGBW™ panel are subpixel rendered, meaning they are drawn at the subpixel level (the individual points of light), rather than to the whole pixels of an RGB stripe display. In fact "pixels" in the traditional sense have been eliminated in PenTile RGBW™ displays; individual subpixels are not restricted to use in one pixel group, but instead participate in multiple "logical" pixels in their surrounding vicinity.

Subpixel rendering dramatically increases addressability and enables the sophisticated image processing used in PenTile RGBW™ displays.


Why add a white subpixel?

LCDs are highly inefficient. Because RGB color filters transmit only a small band of wavelengths, only a small percentage of the light generated by an LCD’s backlight is visible to the eye, which reduces brightness. PenTile RGBW™ displays add a white subpixel to the RGB mix that is actually a clear area in the LCD with no color filter material; therefore nearly all of the light is transmitted through the white subpixel. PenTile’s sophisticated software algorithms capitalize on this efficiency to create sharp images and brighter displays.

The addition of white subpixels combined with increased subpixel width makes PenTile RGBW™ panels about twice as transmissive as comparable RGB stripe LCDs.

PenTile® technology renders the same resolution as RGB stripe with 33% fewer subpixels

The human eye perceives the resolution of the PenTile RGBW™ panel as the same as an equivalent RGB stripe panel, yet the PenTile® panel uses one-third fewer subpixels. Consider the figure below to understand how this is accomplished.

Rgb V Rgbw Circle Chart

At the top is the PenTile RGBW™ layout; at the bottom RGB stripe. The circle at the bottom center demonstrates the finest pattern of vertical black and white lines an RGB stripe display is capable of rendering. This requires three columns (R + G + B) be turned "on" and an equivalent width of three columns be turned "off" to write one cycle of a black and white line. From a suitable distance this collection of color subpixels appears to the eye as a white line.

The top center circle shows the equivalent pattern of vertical black and white lines written to the PenTile RGBW™ layout. From a distance the array of color subpixels in two columns will appear to the eye as a white line, identical to that generated by the RGB stripe layout, and the following two columns will write the corresponding black line. With only four columns being used to accomplish the same linear cycle that required six columns for legacy RGB stripe, two columns are saved. Hence, PenTile RGBW™ technology maintains the same resolution with one-third fewer columns, one-third fewer subpixels and one-third fewer transistors in the array. This results in wider columns and improved aperture ratio (ratio of transmissive area of a subpixel to the total area of that subpixel).

The circles on the right of the figure demonstrate the finest pattern of black and white lines which may be written horizontally to RGB stripe (bottom) and PenTile RGBW™ (top). Note that both layouts require the same number of rows for horizontal lines.

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