The word pixel is a portmanteau of the words picture and element. Sometimes abbreviated as “px”, a pixel is the smallest possible unit of an image displayed on a digital screen. They’re the small, colored squares that blend together to make up the images you see on your computer screen or mobile device.
Pixels are an important technical aspect of digital creative, especially when it comes to designing websites that follow modern web design best practices. Web designers leverage their technical understanding of pixels to build responsive websites that scale automatically to fit the user’s device, regardless of screen size or display resolution.
Digital displays like computer monitors, mobile phones, and tablets use pixels and the RGB color model to represent images on a digital screen. RGB is an additive color model where the light source within the display device creates the desired color by mixing red, green, and blue, and varying their intensity.
An RGB display is made up of millions of pixels. When it’s time to display an image, each of those pixels receives a small segment of binary code that tells it how to display a certain color. When every pixel is displaying the right color, the colors blend together and the bigger picture becomes discernible for users.
Here’s what you need to know about how pixels work:
A pixel is a logical unit – not a physical unit – so there is no standard size for the pixels that make up a digital display. Different digital products implement pixels in different sizes, though they are ordinarily square or rectangular in shape.
In an RGB display, each pixel has red, blue, and green color elements. Each of these color elements can be expressed at a different intensity (also called saturation), from 0 (least saturated) to 255 (most saturated).
By combining different saturation levels of these three color elements, a pixel can be made to represent over 16 million different colors.
The pixels on a typical digital display are arranged in a grid, with rows of pixels from left to right and columns of pixels from top to bottom. Every pixel in the grid has its own unique address or coordinates. This address is used to transmit the code that determines which color the pixel should display.
A digital camera takes pictures by focusing light on a silicon sensor. This sensor consists of a grid of light-sensitive photosites known as pixels. When you snap a photo, the sensor measures the color and brightness of each pixel and stores it as a number.
Thus, a digital photograph is really just a long string of numbers with the address and color information for every pixel needed to reconstruct the image.
Pixels are the building blocks of every image we see on a digital display. The quality of those images depends on:
A vector image uses point-to-point mathematical calculations to form lines and shapes. As a result, vector images can maintain the exact same quality when scaled up or down. In contrast, a raster or bitmap image is made of colored pixels. Zooming in on such an image creates an effect known as “pixelation” where users can see the rectangular outlines of the pixels. A low-resolution image shown on a high-resolution screen will also appear blurry or pixelated.
The quality of image on a digital display depends on Pixel Density – the number of pixels that fit into a square-inch of the screen. Pixel Density depends on both the screen size and the display resolution.
A smaller screen with higher display resolution (more total pixels on screen) will have a greater pixel density and images will appear clear, crisp, and refined. As screens get larger and display resolution smaller, pixel density decreases and high-resolution images can start to appear blocky or pixelated.
The following table lists some common devices, along with their screen sizes, display resolution, and pixel density:
| Device | Screen Size | Display Resolution | Total Pixels | Pixel Density (PPI) |
| Apple iPhone 12 | 6.1” | 2532 x 1170 px | 3 MP | 460 PPI |
| Google Pixel 6 | 6.4” | 1080 x 2400 px | 2.6 MP | 512 PPI |
| 4th Generation iPad | 9.7” | 2048 x 1536 px | 3 MP | 264 PPI |
| Standard 21-inch Monitor | 21” | 1920 x 1080 px (1080p Resolution) | 2 MP | 105 PPI |
| Modern 27” LED Monitor | 27” | 3840 x 2160 px (4K Resolution) | 8.3 MP | 163 PPI |
Web designers depend on their knowledge of pixels to build functional and attractive websites that deliver an optimized user experience (UX). So far, our discussion of pixels has been focused on hardware pixels – the pixels that make up digital displays. But web designers actually work directly with software pixels, also known as CSS pixels.
Before the widespread release of high-density displays, life was easy for web designers because 1 CSS pixel = 1 hardware pixel. When a developer wrote a CSS rule that set the width of a website element at 300 px, that declaration mapped directly to 300 pixels on the screen of the user device.
Now that we have high-density displays, each device manufacturer sets a Device Pixel Ratio that determines how many hardware pixels equal a single software pixel. For example, the Device Pixel Ratio of the Samsung Galaxy S20 is around 4.0 (1 CSS Pixel = 4 Hardware Pixels). When a developer writes a CSS rule that sets the width of a website element to 300px, that element would render on the S20 with a width of 1200 px.
This is all part of responsive design, a modern design approach that makes a well-designed website render well and function correctly on all devices, regardless of their screen size, display resolution, or device pixel ratio.
At Directive Consulting, we leverage our expertise in website design as part of our Customer Generation methodology, helping our B2B SaaS clients build dynamic and responsive websites that look amazing and perform exceptionally across the full range of user devices.
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