3 ms·

Then how come a column of white pixels next to a column of black pixels looks perfectly sharp, as sharp as a black sheet of paper on a white background? Whatev

by geofft 6y ago

Then how come a column of white pixels next to a column of black pixels looks perfectly sharp, as sharp as a black sheet of paper on a white background? Whatever pixels "are", they are certainly tools for inducing a certain perception in the eye of the viewer, so we should go by how that works. We're used to this from color itself - no one denies that 0xffff00 is "yellow", despite the physical emission containing no yellow light, because red + green in certain proportions induces the same response in our eyes as light whose wavelength is actually yellow. So why can't we apply the term "squares" to things that our eyes see as squares even if they are not physically squares?

sudosysgen 6y ago
Simple, it absolutely does not at all. Here: https://i.stack.imgur.com/n6snK.png https://i.stack.imgur.com/n6snK.png. Open this in IrfanView, set the magnification to 100%. It looks about 75%-25% dark grey to light grey unless you really focus on it. This is exactly what you would expect if you conceptualize pixels as points. So no, a column of white pixels next to a column of black pixels does not look perfectly sharp. If it did, the image above would look perfectly black and white, with no grey. And by the time I approach the pixels enough to see perfect black vs perfect white, I also notice the black gaps between pixels, and very soon the sub-pixels themselves! This is also why you don't see individual sub-pixels, by the way. Your eyes largely cannot distinguish the individual squares that pixels are if you are using a non-ancient screen. Your eye does not form an image of the square pixel. It largely loses them as they blend into each other to form an image, in which pixels are much, much closer to points than they are to squares.
- Dylan16807 6y ago
  Not 'perfectly' sharp, but if you have a bunch of objects where the edges go from 0 to 200, and you have a bunch of objects where the edges go from 0 to 100 to 200, there is a significant difference in sharpness on most screens.
  - sudosysgen 6y ago
    Sure. And that is also perfectly consistent with considering pixels are dimensionless points forming an image, which they really are in practice much more than they are simply squares. Indeed, an edge that goes from 0 to 100 can be considered as part of a wave of twice the frequency but the same amplitude as compared to an edge that goes from 0 to 200. Which is, by the way, why increasing the contrast in an image, especially micro-contrast, in practice increases resolution.
    - Dylan16807 6y ago
      This is supposed to be an edge with nearly perfect sharpness. If you take a single point sample, then slowly moving objects will appear to jump an entire pixel at a time, looking awful. If you antialias, then movement will look smooth, but you'll also notice than when you align to the pixel squares the edge will preserve its sharpness better. You have to be really careful when you're applying wave equations to resolution, especially when declaring that a certain number of samples fully captures an image. If you want to display a perfect image with point samples, you may need to go as far as 10x the 'retina' density. https://en.wikipedia.org/wiki/Hyperacuity_(scientific_term) https://en.wikipedia.org/wiki/Hyperacuity_(scientific_term)
- geofft 6y ago
  Take a sheet of white paper 10 inches wide and draw 480 evenly spaced vertical lines on that paper. Do you see the lines? Or do you see a gray sheet of paper? Does that mean the lines don't exist?
  - sudosysgen 6y ago
    I don't care that they exist, I care that they >looks perfectly sharp, as sharp as a black sheet of paper They don't. Pixels are so small that they they start looking like (or are well into looking like) a sample that is used to from an image. If pixels "looked perfectly sharp, as sharp as a black sheet of paper", this wouldn't be the case. As far as your eyes, the sharp lines might as well be blurry waves of an appropriate contrast. So in an image sense, the lines don't really exist anymore, all that exists is a blurry brightness function and not infinitely sharp lines.

by geofft 6y ago

sudosysgen 6y ago

Simple, it absolutely does not at all. Here: https://i.stack.imgur.com/n6snK.png https://i.stack.imgur.com/n6snK.png. Open this in IrfanView, set the magnification to 100%. It looks about 75%-25% dark grey to light grey unless you really focus on it. This is exactly what you would expect if you conceptualize pixels as points. So no, a column of white pixels next to a column of black pixels does not look perfectly sharp. If it did, the image above would look perfectly black and white, with no grey. And by the time I approach the pixels enough to see perfect black vs perfect white, I also notice the black gaps between pixels, and very soon the sub-pixels themselves! This is also why you don't see individual sub-pixels, by the way. Your eyes largely cannot distinguish the individual squares that pixels are if you are using a non-ancient screen. Your eye does not form an image of the square pixel. It largely loses them as they blend into each other to form an image, in which pixels are much, much closer to points than they are to squares.

Dylan16807 6y ago
Not 'perfectly' sharp, but if you have a bunch of objects where the edges go from 0 to 200, and you have a bunch of objects where the edges go from 0 to 100 to 200, there is a significant difference in sharpness on most screens.
- sudosysgen 6y ago
  Sure. And that is also perfectly consistent with considering pixels are dimensionless points forming an image, which they really are in practice much more than they are simply squares. Indeed, an edge that goes from 0 to 100 can be considered as part of a wave of twice the frequency but the same amplitude as compared to an edge that goes from 0 to 200. Which is, by the way, why increasing the contrast in an image, especially micro-contrast, in practice increases resolution.
  - Dylan16807 6y ago
    This is supposed to be an edge with nearly perfect sharpness. If you take a single point sample, then slowly moving objects will appear to jump an entire pixel at a time, looking awful. If you antialias, then movement will look smooth, but you'll also notice than when you align to the pixel squares the edge will preserve its sharpness better. You have to be really careful when you're applying wave equations to resolution, especially when declaring that a certain number of samples fully captures an image. If you want to display a perfect image with point samples, you may need to go as far as 10x the 'retina' density. https://en.wikipedia.org/wiki/Hyperacuity_(scientific_term) https://en.wikipedia.org/wiki/Hyperacuity_(scientific_term)
geofft 6y ago
Take a sheet of white paper 10 inches wide and draw 480 evenly spaced vertical lines on that paper. Do you see the lines? Or do you see a gray sheet of paper? Does that mean the lines don't exist?
- sudosysgen 6y ago
  I don't care that they exist, I care that they >looks perfectly sharp, as sharp as a black sheet of paper They don't. Pixels are so small that they they start looking like (or are well into looking like) a sample that is used to from an image. If pixels "looked perfectly sharp, as sharp as a black sheet of paper", this wouldn't be the case. As far as your eyes, the sharp lines might as well be blurry waves of an appropriate contrast. So in an image sense, the lines don't really exist anymore, all that exists is a blurry brightness function and not infinitely sharp lines.