Summary
- Each pixel in a digital display has subpixels that impact image quality, sharpness, cost, and color accuracy.
- Subpixel arrangements like pentile and RGBW affect how colors are displayed, resolution, and viewing angles.
- Understanding subpixel structures can help you choose a screen that minimizes color distortion and maximizes image clarity.
Every modern flat panel display consists of physical “pixels” or “picture elements” that make up the image as a whole. Pixels are already tiny, but each one is a complex machine in its own right, with numerous independent parts.
There are different ways to put together a display at the subpixel level, and these tiny differences can have significant effects on how your screen looks and performs. So let’s cover the basics of subpixels, and how they might influence your next gadget purchase.
What Are Subpixels?
A pixel is the smallest component of a digital image. Each pixel has a color value, and so when you set the color of each one just right, you get a reproduction of the original image.
Using the macro mode of my iPhone, you can just barely see the subpixels of each pixel in an iPad Pro mini-LED screen.
The physical pixels in a flat panel display have subcomponents known as subpixels. Typically, but not always, there are three subpixels. One for red, one for green, and one for blue. The predecessor to flat panel displays, CRT screens, used three electron beams instead, corresponding to each color.
By adjusting the intensity of each subpixel, you can recreate just about any color. This is why you can sample a color from a digital image and get its RGB value. These are literally the numerical values for each subpixel.
How Subpixels Affect Display Quality
There are a few different ways to construct and arrange subpixels and this subpixel structure affects how sharp or color-accurate a display is, as well as how much it costs to make.
Resolution and Sharpness
A great example of how much subpixel structure matters is the pentile subpixel arrangement. While you’d usually expect each pixel to have its own set of three subpixels in a standard RGB arrangement, pentile displays actually share subpixels between pixels. For example, you can have two green and two red subpixels for each blue subpixel. The main advantage of this is that you can pack more pixels into a small space, which is why most mobile phone screens use this arrangement.
Pentile displays work because of how our eyes perceive red,blue, and green light differently. In short, we have significantly fewer cone cells for blue light than red or green, and so reducing the number of blue subpixels doesn’t really degrade the image, or our perception of how bright and vibrant it is. Pentile displays do have some issues with color “leakage” or image distortion that needs to be compensated for, but is less apparent on a 6-inch screen. The pixels from the image are “subsampled” onto “logical” pixels in the display that are either centered on a green or red subpixel, and these neighboring logical pixels share blue subpixels.
Color Accuracy
Some subpixel structures add a fourth subpixel. This is usually either a white (RGBW) or yellow (RGBY) subpixel. These subpixels can help enhance the brightness of the display, or how wide the color gamut is.
However, it’s not only the number and type of subpixels that matter, but also how they are arranged. Some arrangements can cause color fringing, or affect viewing angles.
Related
Viewing Angles and Uniformity
The way subpixels are aligned impacts how a display looks from different angles. Technologies like IPS (In-Plane Switching) use a specific subpixel arrangement that allows for better viewing angles compared to TN (Twisted Nematic) panels, which may shift in color when viewed from the side.
One good example is Samsung’s “dual pixel” layout in its QLED TVs, which splits a pixel into two domains and drives them slightly differently to improve the viewing angles of the display. Something that’s pretty important in a TV compared to a monitor.
Text Rendering and Clarity
A macro shot of text rendered on an LCD in Windows. Notice how the subpixels around the edges of the text are used to smooth out each letter.
Text clarity is also influenced by subpixel rendering techniques like ClearType (Windows) and Subpixel Anti-Aliasing (in macOS before Mojave). These methods take advantage of the human eye’s perception of color to smooth out text edges, making it more readable on LCD screens. This is why ClearType only works properly on an LCD and not on a CRT, because it compensates for the specific pixel geometry of that display technology. With modern displays that have extremely high pixel densities (e.g. Apple’s Retina Displays) this isn’t necessary anymore since the pixels are so tiny.
Subpixels and Display Technologies
Different display technologies use subpixel geometry in unique ways to optimize for the strength of that technology:
- LCD (Liquid Crystal Display): Uses a backlight and liquid crystal layer to control RGB subpixels. Variations like IPS, TN, and VA affect color accuracy and viewing angles.
- OLED (Organic Light-Emitting Diode): Each subpixel emits its own light, allowing for true blacks and infinite contrast. OLED screens often use WRGB subpixels to improve brightness.
- MicroLED: Functions like OLED but with even better efficiency and longevity, using self-emissive RGB subpixels that are each an independent LED. So there’s no backlight.
- E Ink (Electronic Ink): Found in e-readers, some E Ink displays use a form of grayscale subpixel manipulation to create sharper text and images.
Why Subpixels Matter to You
So this is all interesting for display nerds, but what does it matter to the average person? The long and short of it is that if you’re looking to buy a new monitor, TV, or device with a screen, it’s worth looking up what the subpixel geometry of that device is. This can help you understand if you’re going to face specific shortcomings or advantages in that device.
For example, some people simply don’t like how some of Samsung’s past pentile phone displays looked, and that was enough reason to avoid them and go for something else. It also helps you understand why OLED or microLED technology can outperform backlit LCD displays, or why QLEDs manage such good color vibrancy.
If you want to dig into all the different subpixel layouts. I suggest checking out Geometrian’s Subpixel Zoo, which has numerous excellent microscopic photos of pixel layouts along with the pros and cons of each.
