A pixel is commonly misunderstood as solely a unit of area, like a tiny square on a screen. However, it's more accurate to consider a pixel as having both length and area. The length of a pixel refers to the distance between two adjacent pixel centers, influencing measurements like DPI (dots per inch). Pixel area is derived from this length, representing the visible square or rectangular region on the display. While often used interchangeably, distinguishing between pixel length and area is important for calculations involving display resolution, image scaling, and other graphical computations, ensuring accuracy and preventing potential confusion.
The concept of a "pixel" often leads to confusion due to its dual nature as both a unit of length and a unit of area. This ambiguity stems from the discrete and quantized nature of digital images, unlike continuous analog representations. A digital image is fundamentally a grid of individual picture elements, each representing a single color or shade. Each of these elements, a pixel, occupies a specific location and has a finite, albeit small, physical size.
When we discuss pixel dimensions, such as the width or height of an image, we are implicitly referring to a count of pixels along that dimension. For instance, an image declared as 800 pixels wide signifies it comprises 800 individual pixel elements arranged horizontally. In this context, the "pixel" acts as a unit of length, akin to saying an object is 800 units wide. However, it's crucial to recognize that this length is not expressed in absolute physical units like millimeters or inches; rather, it represents a count of discrete elements.
Simultaneously, a pixel also represents a unit of area. Each pixel occupies a physical space on the display, and the overall area of the image is the sum of the areas of all its constituent pixels. A single pixel can be visualized as a tiny square or rectangle on the display surface. Therefore, when discussing the total number of pixels in an image, we effectively describe its area in terms of "square pixels." For example, an 800 by 600 image has an area of 480,000 square pixels. Again, this area isn't in absolute units like square millimeters; it's a quantized measure based on the number of individual pixel elements.
The potential for misunderstanding arises from the common practice of omitting the "square" prefix when discussing pixel area. While technically imprecise, it's often understood through context. The article emphasizes that understanding this duality – pixel as a unit of length and a unit of area – is essential for clear communication and accurate calculations related to digital images and display resolutions. This comprehension helps avoid errors and ambiguities when working with image scaling, aspect ratios, and other image-related computations. The precise physical dimensions of a pixel depend on the specific display device and its resolution, introducing another layer of complexity when translating pixel counts to real-world measurements.
Summary of Comments ( 91 )
https://news.ycombinator.com/item?id=43769478
HN commenters largely agree with the article's premise that "pixel" can refer to both length and area. Some point out the context usually makes the meaning clear, similar to how "foot" can describe length or square footage. Others discuss the distinction between device pixels, CSS pixels, and other pixel variations, highlighting the importance of specifying which type of pixel is being discussed. A few commenters suggest the ambiguity arises from conflating the pixel count (area) with the physical size it represents (length). One commenter humorously likens using pixels for area to ordering a screen by the number of pixels instead of physical dimensions, imagining ordering a 1920x1080 inch screen instead of a standard size. Finally, some users offer alternative ways to express length in web design, like using relative units such as
remandem.The Hacker News post "Pixel is a unit of length and area" generated a moderate amount of discussion, with several commenters exploring nuances and offering differing perspectives on the article's premise.
One of the most compelling threads began with a user pointing out that the article overlooks the context of "device pixels" versus "CSS pixels". They explained that CSS pixels are abstract units designed for layout, while device pixels represent the physical hardware. This distinction is crucial for understanding how browsers handle scaling and resolution differences. Other users built upon this, elaborating on the roles of
devicePixelRatioand the complexities of achieving consistent rendering across diverse devices. This discussion highlighted the practical considerations that web developers face when working with pixels in a real-world environment.Another commenter raised the issue of square versus non-square pixels. They noted that while often assumed to be square, pixels can be rectangular, particularly in older or specialized display technologies. This observation added another layer to the discussion, reminding readers that the simple concept of a "pixel" can have subtle variations.
Several users expressed appreciation for the article's clarity in explaining a commonly misunderstood topic. They found the explanations of pixel density and the relationship between length and area in the context of pixels to be helpful.
Some users mentioned the challenges of working with different coordinate systems, highlighting the differences between screen coordinates and pixel coordinates. This tied back to the earlier discussion on device pixels versus CSS pixels, reinforcing the importance of context when discussing pixel measurements.
Finally, a few comments focused on the historical context of pixels, referencing early computer graphics and the evolution of display technology. This historical perspective provided an interesting backdrop to the more technical points raised in other comments.
Overall, the comments on the Hacker News post enriched the discussion around the concept of pixels, moving beyond the article's core points to explore practical implications, historical context, and the complexities of modern display technologies.