What is PPI? Decoding the Index and Its Meaning in Display Technology

In the world of display technology, PPI is a term that frequently appears, especially when comparing devices like smartphones, tablets, or computer monitors. But exactly what isWhat is PPI and what does it signify for our viewing experience? This article will delve into the concept of PPI, how it is calculated, and its importance.

What is PPI? Understanding the concept of Pixels Per Inch

PPI stands for "Pixels Per Inch." This is an index that measures the pixel density of a screen, indicating how many pixels are displayed per square inch of that screen. The higher the pixel density, the sharper and smoother the image displayed on the screen.

To visualize it easily, imagine a picture made up of millions of tiny dots. The denser these dots are, the more detailed and clear the picture will be. PPI is similar; the closer the pixels are, the harder it is for the human eye to distinguish individual pixels, giving the image a more seamless and realistic feel.

Phân biệt PPI và DPI

When talking about pixel density, we sometimes also hear the term DPI (Dots Per Inch). While seemingly similar, PPI and DPI are not entirely the same.

• PPI (Pixels Per Inch):Used to refer to the pixel density of digital display devices such as phone screens, computers, and TVs. This is the number of physical pixels per inch of the screen.
• DPI (Dots Per Inch):Commonly used to refer to the density of ink dots per inch of a printout. It relates to the printing capability of the printer and the quality of the printed document.

In the context of display technology, when we talk about display quality, the precise term to use is PPI.

Calculating the PPI

To calculate a screen's PPI, we need two parameters: the screen resolution (number of pixels horizontally and vertically) and the screen's diagonal size (measured in inches).

The formula for calculating PPI is as follows:

PPI = √ (Horizontal Resolution² + Vertical Resolution²) / Diagonal Size

For example, a Samsung Galaxy S24 Ultra phone has a 6.8-inch screen with a resolution of 3120 x 1440 pixels.

• Horizontal Resolution = 3120
• Vertical Resolution = 1440
• Diagonal size = 6.8 inches

Apply the formula:

PPI = √ (3120² + 1440²) / 6.8PPI = √ (9734400 + 2073600) / 6.8PPI = √ (11808000) / 6.8PPI = 3436.27 / 6.8PPI ≈ 505 PPI

With a PPI of 505, the Galaxy S24 Ultra delivers an extremely sharp display experience, making it difficult to distinguish individual pixels with the naked eye at normal viewing distances.

The importance of PPI for user experience

The PPI directly affects the display quality and the user's visual experience.

Image sharpness and detail

A screen with high PPI will display images, text, and graphics with higher sharpness and detail. Edges will be smoother, without jaggedness. This is especially important for those whose work demands high image precision, such as graphic design, photo editing, video editing, or playing graphics-intensive games.

For example, a user working in graphic design in HCMC would typically look for a computer monitor with high PPI, such as the Dell UltraSharp U2723QE (27-inch, 4K, approximately 163 PPI) or the LG UltraFine 5K (27-inch, 5K, approximately 218 PPI) to ensure color accuracy and detail when working.

Reading and content viewing experience

With high PPI, text on the screen will be clearer and easier to read, reducing eye strain during long reading sessions. This is extremely useful for those who frequently read e-books, online newspapers, or work with text documents on phones and tablets.

Suppose you are comparing two mid-range mobile phones in Vietnam, such as the Xiaomi Redmi Note 13 Pro+ (6.67 inches, 2712 x 1220 pixels resolution, PPI around 446) and another phone model with a lower PPI, you will notice a distinct difference in the smoothness of letters and the sharpness of application icons.

Retina Display

The term "Retina Display," introduced by Apple, is not a specific screen technology but rather a PPI standard. It refers to a display with a pixel density high enough that the human eye cannot distinguish individual pixels at a normal viewing distance. For phones, this threshold is typically around 300 PPI or more. For tablets, it can be slightly lower due to a longer viewing distance.

Apple products like the iPhone 15 Pro Max (460 PPI) or the MacBook Pro 16 inch (254 PPI) both meet Retina standards, providing an excellent visual experience for users in Vietnam and worldwide.

Ideal PPI for each device type

There isn't a "best" PPI number that applies to all types of devices. The ideal PPI depends on the screen size and the user's typical viewing distance.

• Smartphone:Held close to the eyes, phones require a very high PPI for sharp images. Around 300-500 PPI is considered ideal, with many current flagship models exceeding 400 PPI. For example, the 6.7-inch iPhone 15 Pro Max with a resolution of 2796 x 1290 pixels has a PPI of approximately 460.
• Tablets:With a viewing distance slightly further than a phone, a PPI of 250-350 is good enough. The iPad Pro M4 13-inch (2752 x 2064 pixels) has a PPI of around 264, delivering detailed and sharp images.
• Computer screen:Because users sit further from the screen, PPI can be lower. A 24-inch Full HD (1920x1080) monitor has a PPI of about 92, while a 27-inch 4K (3840x2160) monitor has a PPI of about 163, providing superior sharpness.
• TV:With long viewing distances, TVs don't need very high PPI. A 55-inch 4K TV has a PPI of around 80, but still provides an excellent viewing experience due to the long viewing distance.

Conclusion

PPI is an important indicator for evaluating screen display quality. The higher the pixel density, the sharper, more detailed, and easier to view the image, providing a better visual experience for users. When choosing to buy a phone, tablet, computer monitor, or TV, considering the PPI index, alongside resolution and size, will help you make a decision that suits your needs and usage purposes. A good visual experience not only helps you work more efficiently but also provides comfort and enjoyment when entertaining.