A Pixel Is Not a Little Square (1995) [pdf]
alvyray.com
A Pixel Is Not a Little Square (1995) [pdf]
1–10 of 31 posts
Re: A Pixel Is Not a Little Square (1995) [pdf]
#2See also: Pixel is a unit of length and area - https://news.ycombinator.com/item?id=43769478 - 1 hour ago (11 points, 20 comments)
Re: A Pixel Is Not a Little Square (1995) [pdf]
#3Never really convinced me; I've done lots of graphics stuff, and I find thinking about pixels as squares works fine. Under magnification, LCD pixels are usually square blocks of rectangular RGB segments (OLED and phone screens can be stranger geometry), and camera sensors are usually made of square (ish) pixel sensor blocks in a Bayer colour array pattern. They're not point sources or point samples, they emit or sense light over an area. Maybe I'm missing something.
Lots of past discussions:
https://news.ycombinator.com/item?id=35076487 74 points, 2 years ago, 69 comments
https://news.ycombinator.com/item?id=26950455 81 points, 4 years ago,70 comments
https://news.ycombinator.com/item?id=20535984 143 points, 6 years ago, 79 comments
https://news.ycombinator.com/item?id=8614159 118 points, 10 years ago, 64 comments
https://news.ycombinator.com/item?id=1472175 46 points, 15 years ago, 20 comments
Re: A Pixel Is Not a Little Square (1995) [pdf]
#4This classic article is wrong, BTW, there's no nicer way to put it. It applies the wrong theory. It was already wrong in 1995 when monitors where CRTs, and it's way wrong in 2025 in the LCD/OLED era where pixels are truly discrete.
Audio samples are point samples (usually). This is nice, because there's a whole theory on how to upsample point samples without loss of information. But more importantly, this theory works because it matches how your playback hardware functions (for both analog and digital reasons that I won't go into).
Pixels, however, are actually displayed by the hardware as little physical rectangles. Take a magnifying glass and check. Treating them as points is a bad approximation that can only result in unnecessarily blurry images.
I have no idea why this article is quoted so often. Maybe "everybody is doing it wrong" is just a popular article genre. Maybe not everyone is familiar enough with sampling theory to know exactly why it works in audio (to see why those reasons don't apply to graphics).
Re: A Pixel Is Not a Little Square (1995) [pdf]
#5Except pixels are little squares. Sure, if you look under a microscope, they have funny shapes, but they are always laid out in a rectangular grid. I've never seen any system where the logical pixels are staggered like a hex grid, for example. No matter how the actual light emitters are arranged, the abstraction offered to the programmer is a rectangular grid.
If you light up pixels in a row, you get a line - a long thin rectangle - and not a chain of blobs. If you light them up diagnoally, you get a jagged line. For me that is proof that they squares - at least close enough to squares. Heck even on old displays that don't have a square pixel ratio they are squished squares ;-). And you have to treat them like little squares if you want to understand antialiasing, or why you sometimes have to add (0.5, 0.5) to get sharp lines.
(And a counterpoint: The signal-theoretical view that they are point samples is useful if you want to understand the role of gamma in anti-aliasing, or if you want to do things like superresolution with RGB-sub-pixels.)
Re: A Pixel Is Not a Little Square (1995) [pdf]
#6This classic article is wrong, BTW, there's no nicer way to put it. It applies the wrong theory. It was already wrong in 1995 when monitors where CRTs, and it's way wrong in 2025 in the LCD/OLED era where pixels are truly discrete. Audio samples are point samples (usually). This is nice, because there's a whole theory on how to upsample point samples without loss of information. But more importantly, this theory work…
I think you're wrong. According to my knowledge the pixels on CRT were rectangular and were throwing their color on neighbouring pixels. Graphics created for CRT were shown nicely on those screens, had much better visuals than displayed on LCD/LED and were antialiases by default (i.e. by the display technology)
Re: A Pixel Is Not a Little Square (1995) [pdf]
#7Except pixels are little squares. Sure, if you look under a microscope, they have funny shapes, but they are always laid out in a rectangular grid. I've never seen any system where the logical pixels are staggered like a hex grid, for example. No matter how the actual light emitters are arranged, the abstraction offered to the programmer is a rectangular grid. If you light up pixels in a row, you get a line - a long…
There are some screen types with variations on the geometry, like some sub-pixels shared between logical pixels. E.g. Samsung's diamond pixel https://global.samsungdisplay.com/29043/, Apple watch https://imgur.com/GkKjjwy. They are still programmed as squares, but the light isn't emitted exactly like that (still coming from discrete areas, not points).
See also https://www.reddit.com/r/apple/comments/9fp1ty/did_you_ever_....
Re: A Pixel Is Not a Little Square (1995) [pdf]
#8Except pixels are little squares. Sure, if you look under a microscope, they have funny shapes, but they are always laid out in a rectangular grid. I've never seen any system where the logical pixels are staggered like a hex grid, for example. No matter how the actual light emitters are arranged, the abstraction offered to the programmer is a rectangular grid. If you light up pixels in a row, you get a line - a long…
I don't remember the manufacturer (may have been Fuji[0]), but someone made a camera sensor that was laid out around a 45-degree angle.
Re: A Pixel Is Not a Little Square (1995) [pdf]
#9This classic article is wrong, BTW, there's no nicer way to put it. It applies the wrong theory. It was already wrong in 1995 when monitors where CRTs, and it's way wrong in 2025 in the LCD/OLED era where pixels are truly discrete. Audio samples are point samples (usually). This is nice, because there's a whole theory on how to upsample point samples without loss of information. But more importantly, this theory work…
I think you're wrong. According to my knowledge the pixels on CRT were rectangular and were throwing their color on neighbouring pixels. Graphics created for CRT were shown nicely on those screens, had much better visuals than displayed on LCD/LED and were antialiases by default (i.e. by the display technology)
Pixels displayed on CRT displays are not squares, but they are not infinitely small dots either. They are much less well-defined blobs, that even overlap with each other.
There is also the complication of composite video signals, where you can't treat pixels as linearly independent components.
Re: A Pixel Is Not a Little Square (1995) [pdf]
#10This classic article is wrong, BTW, there's no nicer way to put it. It applies the wrong theory. It was already wrong in 1995 when monitors where CRTs, and it's way wrong in 2025 in the LCD/OLED era where pixels are truly discrete. Audio samples are point samples (usually). This is nice, because there's a whole theory on how to upsample point samples without loss of information. But more importantly, this theory work…
> Audio samples are point samples (usually). This is nice, because there's a whole theory on how to upsample point samples without loss of information.
This signal processing applies to images as well. Resampling is used very often for upscaling, for example. Here's an example: https://en.wikipedia.org/wiki/Lanczos_resampling
> It was already wrong in 1995 when monitors where CRTs, and it's way wrong in 2025 in the LCD/OLED era where pixels are truly discrete.
I don't think it has anything to do with display technologies though. Imagine this: there is a computer that is dedicated to image processing. It has no display, no CRT, no LCD, nothing. The computer is running a service that is resizing images from 100x100 pixels to 200x200 pixels. Would the programmer of this server be better off thinking in terms of samples or rectangular subdivisions of a display?
Alvy Ray Smith, the author of this paper, was coming from the background of developing Renderman for Pixar. In that case, there were render farms doing all sorts of graphics processing before the final image was displayed anywhere.