by anitil on 4/23/25, 7:20 AM with 176 comments
by Laremere on 4/23/25, 8:38 AM
If I have a bin of apples, and I say it's 5 apples wide, and 4 apples tall, then you'd say I have 20 apples, not 20 apples squared.
It's common to specify a length by a count of items passed along that length. Eg, a city block is a ~square on the ground bounded by roads. Yet if you're traveling in a city, you might say "I walked 5 blocks." This is a linguistic shortcut, skipping implied information. If you're trying to talk about both in a unclear context, additional words to clarify are required to sufficiently convey the information, that's just how language words.
by RedNifre on 4/23/25, 2:41 PM
Isn't a pixel clearly specified as a picture element? Isn't the usage as a length unit just as colloquial as "It's five cars long", which is just a simplified way of saying "It is as long as the length of a car times five", where "car" and "length of car" are very clearly completely separate things?
> The other awkward approach is to insist that the pixel is a unit of length
Please don't. If you want a unit of length that works well with pixels, you can use Android's "dp" concept instead, which are "density independent pixels" (kinda a bad name if you think about it) and are indeed a unit of length, namely 1dp = 158.75 micro meter, so that you have 160 dp to the inch. Then you can say "It's 10dp by 5dp, so 50 square dp in area.".
by tomhow on 4/23/25, 12:31 PM
A Pixel Is Not a Little Square (1995) [pdf] – http://alvyray.com/Memos/CG/Microsoft/6_pixel.pdf
by otikik on 4/23/25, 2:17 PM
And the end pixels are "physical things". Like ceramic tiles on a bathroom wall.
Your wall might be however many meters in length and you might need however squared meters of tile in order to cover it. But still, if you need 10 tiles high and 20 tiles width, you need 200 tiles to cover it. No tension there.
Now you might argue that pixels in a scaled game don't correspond with physical objects in the screen any more. That's ok. A picture of the bathroom wall will look smaller than the wall itself. Or bigger, if you hold it next to your face. It's still 10x20=200 tiles.
by justin_ on 4/23/25, 9:09 AM
> This is an issue that strikes right at the root of correct image (sprite) computing and the ability to correctly integrate (converge) the discrete and the continuous. The little square model is simply incorrect. It harms. It gets in the way. If you find yourself thinking that a pixel is a little square, please read this paper.
> A pixel is a point sample. It exists only at a point. For a color picture, a pixel might actually contain three samples, one for each primary color contributing to the picture at the sampling point. We can still think of this as a point sample of a color. But we cannot think of a pixel as a square—or anything other than a point.
Alvy Ray Smith, 1995 http://alvyray.com/Memos/CG/Microsoft/6_pixel.pdf
by blenderob on 4/23/25, 10:48 AM
When you multiply 3 meter by 4 meter, you do not get 12 meters. You get 12 meter squared. Because "meter" is not a discrete object. It's a measurement.
When you have points A, B, C. And you create 3 new "copies" of those points (by geometric manipulation like translating or rotating vectors to those points), you now have 12 points: A, B, C, A1, B1, C1, A2, B2, C2, A3, B3, C3. You don't get "12 points squared". (What would that even mean?) Because points are discrete objects.
When you have 3 apples in a row and you add 3 more such rows, you get 4 rows of 3 apples each. You now have 12 apples. You don't have "12 apples squared". Because apples are discrete objects.
When you have 3 pixels in a row and you add 3 more such rows of pixels, you get 4 rows of 3 pixels each. You now have 12 pixels. You don't get "12 pixels squared". Because pixels are discrete objects.
Pixels are like points and apples. Pixels are not like metres.
by jefftk on 4/23/25, 5:16 PM
* A small city might be ten blocks by eight blocks, and we could also say the whole city is eighty blocks.
* A room might by 13 tiles by 15 tiles, or 295 tiles total.
* On graph paper you can draw a rectangle that's three squares by five squares, or 15 squares total.
by ChrisMarshallNY on 4/23/25, 9:26 AM
The dot may be physically small, or physically large, and it may even be non-square (I used to work for a camera company that had non-square pixels in one of its earlier DSLRs, and Bayer-format sensors can be thought of as “non-square”), so saying a pixel is a certain size, as a general measure across implementations, doesn’t really make sense.
In iOS and MacOS, we use “display units,” which can be pixels, or groups of pixels. The ratio usually changes, from device to device.
by dusted on 4/24/25, 5:15 PM
So, I don't think it's entirely valid to talk about pixels as if they are pure, one dimensional units..
They're _things_ and you can talk about how many things wide or tall something is, and you can talk about how many things something has. Very much the same way you can with bricks (which are mostly never square) (though tiles are, you never talk about how many kilotiles is in your bathroom either, yet you can easily talk about how many tiles wide or tall a wall is).
So, no, pixels is not a unit in the mathematical sense.. it's an item, in the physical sense.
There are also things like scanners, that may have only one row of pixels on the scanner sensor, it does not have an area of zero, and you don't need to specify that there's one pixel on the other axis, because it's an inherent property of pixels that they have both width and height and thus area in and of themselves.
by ivan_gammel on 4/23/25, 10:19 AM
> That means the pixel is a dimensionless unit that is just another name for 1, kind of like how the radian is length divided by length so it also equals one, and the steradian is area divided by area which also equals one.
But then for some reason decides to ignore it. I don’t understand this article. Yes, pixels are dimensionless units used for counting, not measuring. Their shape and internal structure is irrelevant (even subpixel rendering doesn’t actually deal with fractions - it alters neighbors to produce the effect).
by Sharlin on 4/23/25, 8:34 AM
The issue is muddied by the fact that what people mostly care about is either the linear pixel count or pixel pitch, the distance between two neighboring pixels (or perhaps rather its reciprocal, pixels per unit length). Further confounding is that technically, resolution is a measure of angular separation, and to convert pixel pitch to resolution you need to know the viewing distance.
Digital camera manufacturers at some point started using megapixels (around the point that sensor resolutions rose above 1 MP), presumably because big numbers are better marketing. Then there's the fact that camera screen and electronic viewfinder resolutions are given in subpixels, presumably again for marketing reasons.
by knallfrosch on 4/23/25, 8:19 AM
A chessboard is 8 tiles wide and 8 tiles long, so it consists of 64 tiles covering an area of, well, 64 tiles.
by gilgoomesh on 4/23/25, 12:47 PM
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).
by ttoinou on 4/23/25, 8:50 AM
But it does highlight that the common terminology is imperfect and breaks the regularity that scientists come to expect when working with physical units in calculations
by jmull on 4/23/25, 3:22 PM
It certainly doesn't make sense to mix different meanings in a mathematical sense.
E.g., when referring to a width in pixels, the unit is pixel widths. We shorten it and just say pixels because it's awkward and redundant to say something like "the screen has a width of 1280 pixel widths", and the meaning is clear to the great majority of readers.
by GuB-42 on 4/23/25, 9:05 AM
Sometimes, it is used as a length or area, omitting a conversion constant, but we do it all the times, the article gives out the mass vs force as an example.
Also worth mentioning that pixels are not always square. For example, the once popular 320x200 resolution have pixels taller than they are wide.
by bitwize on 4/23/25, 2:00 PM
by kazinator on 4/23/25, 8:10 PM
It is just word semantics revolving around a synecdoche.
When we say that an image is 1920 pixels wide, the precise meaning is that it is 1920 times the width of a pixel. Similarly 1024 pixels high means 1024 times the height of a pixel. The pixel is not a unit of length; its height or width are (and they are different when the aspect ratio is not 1:1!)
A syntax-abbreviating semantic device in human language where part of something refers to the whole or vice versa is called a synecdoche. Under synecdoche, "pixel" (the whole) can refer to "pixel width" (part or property of the whole).
Just like the synecdoche "New York beats Chicago 4:2" refer to basketball teams in its proper context, not literally the cities.
by webstrand on 4/23/25, 5:03 PM
The critical distinction is the inclusion of a length dimension in the measurement: "1920 pixels wide", "3 mount everests tall", "3.5 football fields long", etc.
by forrestthewoods on 4/23/25, 8:35 AM
by JimDabell on 4/23/25, 9:22 AM
by _wire_ on 4/23/25, 3:54 PM
Pixel is an abbreviation for 'picture element' which describes a unit of electronic image representation. To understand it, consider picture elements in the following context...
(Insert X different ways of thinking about pictures and their elements.)
If there is a need for a jargon of mathematical "dimensionality" for any of these ways of thinking, please discuss it in such context.
Next up:
<i>A musical note is a unit of...</i>
by rbanffy on 4/23/25, 2:43 PM
by surfingdino on 4/23/25, 8:26 AM
by thehours on 4/23/25, 8:24 AM
by tuzemec on 4/23/25, 5:33 PM
by Aldipower on 4/23/25, 9:14 AM
by scotty79 on 4/23/25, 4:11 PM
by fennecbutt on 4/23/25, 2:36 PM
by teknopaul on 4/23/25, 4:58 PM
A "megapixel" is simply defined as 1024 pixels squared ish.
There is no kilopixel. Or exapixel.
No-one doesn't understand this?
by alzamixer on 4/23/25, 6:01 PM
So an image could be 1 mega pixel, or 1000 times 1000 pixel-lengths.
by anitil on 4/23/25, 7:20 AM
by nout on 4/23/25, 7:41 PM
by jrvieira on 4/23/25, 12:39 PM
by dullcrisp on 4/23/25, 12:35 PM