Why Are Image Pixels Squares and Not Circles or Rectangles?

The question of why image pixels are square has historical, practical, and technological reasons behind it. Let's delve into the reasons why square pixels are more prevalent in digital imaging than circles or rectangles.

1. Simplicity in Design

Square pixels offer several advantages when it comes to image processing and display. Implementing square pixels simplifies the calculations involved in rendering images, especially during scaling or transformation processes. This uniformity makes the mathematical operations more straightforward, ensuring that the image quality remains intact regardless of the scale.

2. Grid Alignment

Most digital displays are inherently grid-based, with each pixel corresponding to a grid cell on the screen. Square pixels fit seamlessly into this grid structure, allowing for precise alignment and mapping of images to the display. This alignment ensures that images are displayed with the intended quality and proportions, without the need for extensive calibration.

3. Standardization

The use of square pixels has become a standard in digital imaging due to early design choices in television and computer displays. This standardization has led to widespread compatibility across devices and software. Other pixel shapes, such as circles or rectangles, might complicate this compatibility, causing issues with display and interoperability.

4. Aspect Ratio Management

Square pixels are particularly useful in maintaining consistent aspect ratios across images and displays. If pixels were not square, it would complicate the stretching or compressing of images, leading to potential distortions or other quality issues. Square pixels provide a cleaner, more uniform representation of images, ensuring that the visual experience remains consistent.

5. Performance

Processing power and memory considerations also favor square pixels. Algorithms for rendering and manipulating images are generally more efficient when working with square shapes. This efficiency translates to faster processing times and lower memory usage, which are crucial in real-time applications such as video streaming or gaming.

However, it is important to note that not all physical pixels are square. For example, in some advanced displays like AMOLED screens, individual pixels might not be square. As a close-up of an AMOLED screen or a Samsung S8 may show, the pixels can be closer to a triangular or even hexagonal shape. This can be due to the specific technology used, such as inorganic or organic materials, which allow for more varied pixel shapes.

6. The Concept of a Pixel

The term "pixel" is a contraction of "picture element," and while it is an abstract concept representing a digital image, the typical shape of a pixel is a square. In some specialized applications, such as certain types of digital imaging or specialized displays, circular or rectangular pixels might be used. However, for the vast majority of general usage, square pixels remain the most common.

The concept of a "point pixel" is often used, but it is usually mapped to a square grid. For instance, in a color CRT display, you might see small red, green, and blue dots arranged in a triangular grid. Each combination of these dots typically represents more than one pixel. In modern technologies like LCD screens, there is a much closer relationship between digital pixels and the dedicated areas of the screen itself.

When such a screen is driven by a VGA signal, it is actually converting an analog scan, so the agreement between digital pixels and physical display elements is not always precise. This conversion can introduce minor distortions or discrepancies, but in most practical applications, square pixels are used to maintain consistency and ease of use.

In conclusion, while there are exceptions in specialized applications, square pixels remain the most common and practical choice in digital imaging due to their simplicity, alignment, standardization, aspect ratio management, and performance benefits.