Comment by gilgoomesh
5 days ago
A pixel is two dimensional, by definition. It is a unit of area. Even in the signal processing "sampling" definition of a pixel, it still has an areal density an is therefore still two-dimensional.
The problem in this article is it incorrectly assumes a pixel to be a length and then makes nonsensical statements. The correct way to interpret "1920 pixels wide" is "the same width as 1920 pixels arranged in a 1920 by 1 row".
In the same way that "square feet" means "feet^2" as "square" acts as a square operator on "feet", in "pixels wide" the word "wide" acts as a square root operator on the area and means "pixels^(-2)" (which doesn't otherwise have a name).
It is neither a unit of length nor area, it is just a count, a pixel - ignoring the CSS pixel - has no inherent length or area. To get from the number of pixels to a length or area, you need the pixel density. 1920 pixel divided by 300 pixel per inch gives you the length of 6.4 inch and it all is dimensionally consistent. The same for 18 mega pixel, with a density of 300 times 300 pixel per square inch you get an image area of 200 square inch. Here pixel per inch times pixel per inch becomes pixel per square inch, not square pixel per square inch.
CSS got it right by making pixels a relative unit. Meters are absolute. You cannot express pixels in meters. Because they are relative units.
If you have a high resolution screen the a CSS pixel is typically be 4 actual display pixels (2x2) instead of just 1. And if you change the zoom level, the amount of display pixels might actually change in fractional ways. The unit only makes sense in relation to what's around it. If you render vector graphics or fonts, pixels are used as relative units. On a high resolution screen it will actually use those extra display pixels.
If you want to show something that's exactly 5cm on a laptop or phone screen, you need to know the dimensions of the screen and figure out how many pixels you need per cm to scale things correctly. Css has some absolute units but they only work as expected for print media typically.
> The correct way to interpret "1920 pixels wide" is "the same width as 1920 pixels arranged in a 1920 by 1 row".
But to be contrarian, the digital camera world always markets how many megapixels a camera has. So in essense, there are situations where pixels are assumed to be an area, rather than a single row of X pixels wide.
The digital camera world also advertises the sensor size. So a 24MP APS-C camera has smaller pixels than a 24MP Full-frame camera, for example.
> in "pixels wide" the word "wide" acts as a square root operator on the area and means "pixels^(-2)"
Did you meant "pixels^(1/2)"? I'm not sure what kind of units pixels^(-2) would be.
pixel^(-2) is "per squared pixel". Analogously, 1 pascal = 1 newton / 1 metre^2. (Pressure is force per squared length.)
Same as if you were building a sidewalk and you wanted to figure out its dimensions, you’d base it off the size of the pavers. Because half pavers are a pain and there are no half pixels.
> A pixel is two dimensional, by definition.
A pixel is a point sample by definition.
An odd definition. A pixel is a physical object, a picture element in a display or sensor. The value of a pixel at a given time is a sample, but the sample isn't the pixel.
Definitions of technical things you aren’t familiar with tend to be odd.
You are referring to a physical piece of a display panel. A representation of an image in software is a different thing. Hardware and software transforms the dsp signal of an image into voltages to drive the physical pixel. That process takes into account physical characteristics like dimensions.
Oh btw physical pixels aren’t even square and each RGB channel is a separate size and shape.