A Closer Look at the Surface Pro 3 Screen
Reflectivity and Ambient Contrast
Consider the following analogy – When you look up at the night sky how many stars do you see? The answer to that question depends largely on where you are. In a brightly lit city setting you’ll see a limited number of starts. If you leave civilization and find a place in the country with much less light pollution, the night sky will light up with stars. In both places you’re looking at the same sky, but the contrast in the city is low due to ambient light pollution. As a consequence the tiny dots in the sky are hidden. Even the color in the night sky will look more washed out in the city.
For Surface Pro 3, the team wanted the images displayed to appear clear and with pure color, like the sky to the star-gazers in the countryside. Building a great display isn’t a simple task, and for a touch-screen device, this challenge increases because there are materials, e.g., glass, plastic films, air, adhesives, etc. required to create that experience that are all potential sources of “light pollution” that will get between the stargazer and the sky. To accomplish their goal, the team reduced ambient reflected light by engineering a screen with 10% less reflection – both diffuse and specular (mirror-like) – than competitive 10” and 12” touch-screen tablets. The result is great contrast ratio in bright office environments where it’s needed for maximum productivity. When contrast is measured in an actual 500 lux ambient lighting environment (equivalent to what you would find in a bright office) the Surface Pro 3 offers 20% greater contrast ratio than a competitive 12” tablet. Independent analysis by DisplayMate shows very good reflection values and contrast rating (similar to ambient contrast ratio).
Table 1. Comparison of reflection and ambient contrast ratio of Surface Pro 3 vs. a competing product. The reflectance and ambient contrast measurements presented were obtained in Microsoft’s laboratory. Reflectance values may differ depending on angle, light source, etc.
In addition, as shown in Figure 1, the contrast ratio of the Surface Pro 3 remains higher than the competitive device screen over a wide range of angles.
Figure 1. The contrast ratio over horizontal viewing angle of the Surface Pro 3 relative to a competitive 12” touch-screen competitive tablet.
Optical Bonding
From the beginning, the screen on each and every Surface has been optically bonded. This means that the pieces (glass, LCD…) that make up the screen are bonded to each other and that there is no empty space. Optical bonding has three main benefits – increased contrast (reduced glare/reflectance), reduced parallax and increased touch accuracy (described below), and increased mechanical strength and rigidity. Contrast is increased by the fact that there are fewer distinct surfaces to reflect light back at you on an optically bonded display, so images look better as shown in following images.
The optically bonded screen on the right appears much clearer because of reduced reflectivity.
The following three images illustrate how an optically bonded screen creates a crisp and clear image free of reflections on the screen. The multiple reflections of a single touch-point seen on the two images on the left are the result of separation between the LCD and the cover glass.
Text and Image Clarity
Resolution is also important for a high quality display, and the Surface Pro 3 resolution is optimized for the typical viewing distance of approximately 15 – 18 inches. As Figure 2 shows, the average person cannot resolve individual pixels – meaning they can’t distinguish the individual points of color but instead see smooth lines and shapes – when using the Surface Pro 3. This results in sharp and clear text, images, and pictures.
Figure 2. The viewing distance required for an average person to resolve the pixels of a display vs. the pixels-per-inch (PPI) of the display. For the 18” typical viewing distance, the Surface Pro 3 pixels are not resolvable, so lines and shapes appear smooth.
Color Accuracy and Consistency
Not only does the Surface Pro 3 screen offer optimal viewing in ambient lighting and a great clarity, each and every screen is individually calibrated at the factory to ensure the accuracy and consistency of colors. While tablet displays have been achieving ever increasing color gamut (the range of color they can display), we found it best to aim for not only wider color gamut, but for very accurate color in every device.
In camera testing, it is common to use the MacBeth color charts like those shown in Figure 3 to tune the accuracy of color representing most real world images. We use similar color checking methods to ensure that the Surface Pro 3 screen displays images with the intended colors. It is also important that colors are consistent when viewed from different angles. By using a wide-viewing angle LCD, the relative differences between darker and lighter tones (display gamma) and color (chromaticity) appear the same at all viewing angles (see Fig. 3), so that the highly accurate colors do not change over viewing angle. For comparison, DisplayMate measures a JNCD (Just Noticeable Color Difference) average of 2.1, well below their desired threshold of JNCD = 3. The JNCD between normal viewing and 30 degree angle in either portrait or landscape is < 1, giving it very good color accuracy over wide viewing angles.
Parallax and Touch Accuracy
When writing on paper there is no physical separation between pen tip and inking on paper. When writing on a display with a touch screen, there is physical separation between where the stylus/pen tip is touching the glass and where the inking happens on inner layer of the display stack. Parallax is the effective distance between the location a pen touches the top of the device cover glass and the location of the image it generates on the LCD, Figure 3. Figure 3 shows the thin stack-up of the cover glass with integrated touch, the optically clear adhesive (OCA), and the top polarizer and color filter glass of the LCD.
For the user to enjoy a true pen-inking experience we used the thinnest cover glass and touch sensor stack for 12” devices resulting in a 24% thinner “parallax” than a competing 12” touchscreen device with pen. Along with optical bonding of touch screen to LCD, Figure 4, the end result is that the Surface Pro 3 user sees the pen tip meet the resuling image so closely that it appears ink is flowing from the pen on the writing surface.
Figure 3 – Illustration of how the perceived ink location changes from different viewing angles based on the combined thickness of the parts that make up the screen
Figure 4. Schematic of light propagation within the display/touch sensing stack-up. Light deflection occurs at each interface. Note how the absence of an air layer creates a more consistent flow of light and less distance between and actual touch point and perceived touch point. (OCA refers to “Optically-clear adhesive”, which bonds the touch and LCD together.)
You’ll notice the inking accuracy of the pen when you use it, and will love the ease of writing and drawing on your Surface Pro 3. It’s been fun to see the digital art created on Surface Pro devices already, and collectively this art is a great illustration (pun intented) of the accuracy of the pen.
When you pick up a Surface Pro 3, you’ll notice that the screen looks beautiful. There is low reflectivity and high contrast, the colors are accurate from a variety of viewing angles. You’ll notice that the touch and pen experiences are very accurate and very responsive. If you’ve read this far, then you’re interested in the science and engineering that goes in to creating a great screen, and we love sharing the details. In the case of screen performance, however, seeing really is believing. So get to a store and check out the Surface Pro 3 for yourself.
The Surface Screen Team –Stevie, Rajesh, Vicky, Abhijit, Ying, & Andy
P.S. To learn more about the many other product level considerations that drive the Surface Screen Team, check out the invited Society for Information Display paper at: http://onlinelibrary.wiley.com/doi/10.1002/j.2168-0159.2013.tb06141.x/abstract (subscription required)