Pixels Per Inch Explained

Photo by Dawit on Unsplash

Have you ever looked at a product’s detail and seen the words ‘Pixels Per Inch’? Why are the numbers different on each product?

In this article, I will explain what Pixels Per Inch is and why you shouldn’t overlook it when buying a product that has a PPI listed.

Understanding Pixels Per Inch

Pixels Per Inch (PPI) is a fundamental concept in the world of displays and screen technology. It plays a role in determining the sharpness and clarity of images and text on any screen.

What is PPI?

Pixels Per Inch is the number of pixels (the smallest individual units of color and light) that fit into one linear inch of screen surface. In other words, it measures the density of pixels within a given area.

For screens, higher PPI values indicate that there are more pixels per inch, which translates to a finer level of detail and greater sharpness in the displayed content. Conversely, lower PPI values result in larger, more noticeable pixels and a less sharp image.

Generally speaking, the higher the PPI, the better the image quality.

How is PPI Calculated?

PPI can be calculated using the formula:

PPI = √(Width pixels^2 + Height pixels^2) / Diagonal screen size (in inches)

This formula takes into account the total number of pixels in both the width and height of the screen and divides it by the diagonal size of the screen in inches. The square root of this value gives us the PPI.

For example, if you have a computer screen that is 1920 pixels wide by 1080 pixels high and the diagonal is 10 inches. The PPI calculation would look like this:

PPI = √(1920^2 + 1080^2) / 10 = √(3,686,400 + 1,166,400) / 10 = √4,852,800 / 10 = 220,29 PPI

So there are 220,29 pixels in a 1-inch line on the display.

The Relationship Between PPI and Resolution

Now that we’ve understood the concept of Pixels Per Inch (PPI), it’s important to understand how PPI and screen resolution are related.

Resolution vs. PPI

Before diving deeper, let’s distinguish between screen resolution and PPI. Screen resolution refers to the total number of pixels in a screen's horizontal and vertical directions. For instance, a display with a resolution of 1920 x 1080 pixels has 1920 pixels in width and 1080 pixels in height.

On the other hand, PPI is about pixel density, indicating how many pixels are packed into a single linear inch of the screen’s surface. It doesn’t directly define the resolution but rather how finely those pixels are distributed.

Does a Higher PPI Mean a Higher Resolution?

One common misconception is that a higher PPI translates to a better screen resolution. While PPI and resolution have a connection, they are not the same. Here’s how they link up:

• Higher PPI and Image Quality: An increase in PPI usually results in improved image quality and sharpness. This is because more pixels are utilized to represent the same area, which reduces the appearance of individual pixels while boosting image and word clarity.
• Resolution and Total Pixels: Resolution, on the other hand, refers to the total number of pixels on the screen. If the screen size remains constant, a higher resolution means more pixels are spread out across a bigger area. This can also improve image quality, but it does not necessarily imply a greater PPI.
• PPI’s Impact on Screen Size: When you keep the screen resolution unchanged but increase the physical screen size, the PPI decreases. As a result, the pixels become larger and more apparent, and the clarity may suffer.

The Impact of PPI on Screen Sharpness

Now that we’ve covered the fundamentals of PPI and its relationship to screen resolution, let’s go deeper into how PPI affects screen sharpness and visual quality.

What Does ‘Sharpness’ Mean in Screens?

Sharpness refers to the level of detail and clarity perceived by the viewer in images and text on screens and displays. A sharp display produces crisp and well-defined edges, smooth gradients, and brilliant colors, allowing users to read text and enjoy high-quality photos and movies more easily.

The Impact of PPI on Sharpness

Pixels Per Inch (PPI) is one of the key criteria that determines a screen’s sharpness. PPI has the following direct effect on sharpness:

• Higher PPI, Finer Details: Finer details can be displayed on screens with greater PPI values. This is due to the increased density of pixels per inch, which allows for higher precision in producing images and text. Lines appear smoother as a result, and small text is more readable.
• Reduced Pixelation: Pixelation happens when individual pixels become visible, which is most noticeable when seeing images or text up close. A higher PPI reduces the visible size of these pixels, resulting in finer curves and lines, as well as reduced pixelation.
• Enhanced Clarity: High-PPI screens produce crisper and more colorful images. They are particularly good at recreating detailed patterns, textures, and subtle color gradients, contributing to a lifelike and immersive viewing experience.

Below is an example of a low PPI vs. a high PPI image.

Low PPI vs. High PPI | Source: eizo.com

As you can see from the image above, the roughness of the pixels is visible at 96 ppi, but the quality improves dramatically at 192 ppi. The image is much smoother at 384 ppi, and the pixel grains and jagged edges of diagonal lines are no longer evident.

Issues with Increasing PPI

While increasing PPI generally results in clearer screens, there are several considerations:

• Power Consumption: As PPI increases, so does the amount of pixels that must be powered and refreshed. This can result in greater power usage, affecting battery life in portable devices such as smartphones and laptop computers.
• Cost: Because of the precision necessary in generating smaller pixels, producing high-PPI screens can be more expensive. This may have an effect on the price of devices equipped with such displays.
• Diminishing Returns: The human eye may eventually struggle to discern the additional sharpness acquired from excessively high PPI. This raises the question of whether the benefits outweigh the higher costs and power consumption.

By knowing and understanding PPI, I hope you will consider it the next time you want to buy something with a screen and not simply look at its resolution.