4 ms·

The why's in the second to last paragraph of the Quora/Slate article.

ColinWright 8y ago
I disagree. That's still talking about the "how". It's talking about how the scanner works, and how that gives you the result you see. I contend that the statement in that article is still not the "why". I've tried many times to make it clear why I think the Quora article is giving the "how" and not the "why", but I've never been able to convince people of the difference. So why is the scanner designed like this? Even if you didn't know how the scanner works, why is this result an unavoidable consequence of how you want a photocopier to behave? I'd be happy to try to explain this distinction further in an email, but to do so would require giving away the answer, and some people may still want to think about it. My email is (sort of) in my profile. Added in edit: Quoting the article: > To understand why we got the result we did, we first need to look at how a scanner works. My contention is that this statement is wrong, and the result can be deduced from first principles of how a photocopier must behave.
- Anarch157a 8y ago
  My guess is that the paper scaters the light, so the image can bounce on the scanner's mirror, even with a small offset. The mirror, on other hand, reflects in a coherent way, so the light doesn't hit the scanner's reflector.
  - ColinWright 8y ago
    That is what's happening, yes. But that still doesn't explain the why. It would seem that people really don't understand the question I'm asking, and I'm at a loss to find another way of asking it that makes it clearer. Everyone is answering the how, no one is answering the why. Here's another way of asking the question: Based purely on what a photocopier does, and without knowing anything about how it works, can you deduce the result of photocopying a mirror?
    - gus_massa 8y ago
      Let's imagine a photocopier that has a camera that looks at each "pixel" and then it prints the color of the "pixel" to a paper. In this case you can align the light source and the camera and put them perpendicular to the surface of the paper/mirror. So, the mirror will be white instead of black. It's a less efficient design than the standard photocopier model, so nobody uses it. Anyway, this is the main idea of the confocal microscopy. You want to illuminate a very small point with a lot of light, but keep the surrounding parts as dark as posible. You want to see that point. And it's very difficult to aim two optical systems to the same point, so you use the same lens for illumination and for detection. https://en.wikipedia.org/wiki/Confocal_microscopy https://en.wikipedia.org/wiki/Confocal_microscopy
      - ColinWright 8y ago
        Again, that's all true, and all interesting, but it's not answering the question. I'm starting to wonder if this is a difference/distinction that people don't see, and perhaps can't understand[0]. People don't seem to understand the question I'm asking, and I genuinely don't know how to ask it differently. Try to answer the question without referring to how the photocopier/scanner works, and only refer to what it does. If anyone can see the difference, I'd welcome suggestions as to how better to ask the question. [0] Experiments have been done with infants and adults, native French speaking and native English speaking[1]. There are vowel sounds which when played to the infants or the French-speaking adults cause different parts of the brain to light up, but when played to the English speaking adults cause the same place to respond. Not learning French seems to have resulted in the loss of ability to hear the difference between the sounds. Perhaps that ability can be trained and thus regained, but this is an example where not doing something (hearing and recognising the sounds) results in a physiological reason why an ability is lost. Perhaps this distinction between "how" and "why" is an analogous one. [1] For the infants this distinction is moot.
        gus_massa 8y ago
        A mirror has no intrinsic color. The "color" of the mirror is whatever is reflected in it from the camera point of view. If you take a photo of a mirror in a room where there is a single puntual source of light and the walls are far away, and dark to avoid reflection, the mirror will appear black in the photo. If you take a photo of a mirror in a room where there is a very diffuse source of light (like the sky, or a professional diffuse illumination equipment) the mirror will appear white (or sky blue) in the photo. --- My wife make artistic paintings and sometimes she uses shiny mirror-like materials in parts of the frame. It's difficult to take good pictures of them, because you want to make these parts appear shiny, but not too shiny. Also, you don't want too much light reflection in the normal part of the frame. So you must carefully select the angle to take the photo and the position of the lights and how puntual/diffuse they are. (Photographs of a real mirror are also difficult, if you want it to appear like a mirror. There is some reflection of light in the borders, where the glass is cut. And that reflections make it appear as a mirror instead of a plain surface.)

I disagree. That's still talking about the "how". It's talking about how the scanner works, and how that gives you the result you see. I contend that the statement in that article is still not the "why". I've tried many times to make it clear why I think the Quora article is giving the "how" and not the "why", but I've never been able to convince people of the difference. So why is the scanner designed like this? Even if you didn't know how the scanner works, why is this result an unavoidable consequence of how you want a photocopier to behave? I'd be happy to try to explain this distinction further in an email, but to do so would require giving away the answer, and some people may still want to think about it. My email is (sort of) in my profile. Added in edit: Quoting the article: > To understand why we got the result we did, we first need to look at how a scanner works. My contention is that this statement is wrong, and the result can be deduced from first principles of how a photocopier must behave.

Anarch157a 8y ago
My guess is that the paper scaters the light, so the image can bounce on the scanner's mirror, even with a small offset. The mirror, on other hand, reflects in a coherent way, so the light doesn't hit the scanner's reflector.
- ColinWright 8y ago
  That is what's happening, yes. But that still doesn't explain the why. It would seem that people really don't understand the question I'm asking, and I'm at a loss to find another way of asking it that makes it clearer. Everyone is answering the how, no one is answering the why. Here's another way of asking the question: Based purely on what a photocopier does, and without knowing anything about how it works, can you deduce the result of photocopying a mirror?
  - gus_massa 8y ago
    Let's imagine a photocopier that has a camera that looks at each "pixel" and then it prints the color of the "pixel" to a paper. In this case you can align the light source and the camera and put them perpendicular to the surface of the paper/mirror. So, the mirror will be white instead of black. It's a less efficient design than the standard photocopier model, so nobody uses it. Anyway, this is the main idea of the confocal microscopy. You want to illuminate a very small point with a lot of light, but keep the surrounding parts as dark as posible. You want to see that point. And it's very difficult to aim two optical systems to the same point, so you use the same lens for illumination and for detection. https://en.wikipedia.org/wiki/Confocal_microscopy https://en.wikipedia.org/wiki/Confocal_microscopy
    - ColinWright 8y ago
      Again, that's all true, and all interesting, but it's not answering the question. I'm starting to wonder if this is a difference/distinction that people don't see, and perhaps can't understand[0]. People don't seem to understand the question I'm asking, and I genuinely don't know how to ask it differently. Try to answer the question without referring to how the photocopier/scanner works, and only refer to what it does. If anyone can see the difference, I'd welcome suggestions as to how better to ask the question. [0] Experiments have been done with infants and adults, native French speaking and native English speaking[1]. There are vowel sounds which when played to the infants or the French-speaking adults cause different parts of the brain to light up, but when played to the English speaking adults cause the same place to respond. Not learning French seems to have resulted in the loss of ability to hear the difference between the sounds. Perhaps that ability can be trained and thus regained, but this is an example where not doing something (hearing and recognising the sounds) results in a physiological reason why an ability is lost. Perhaps this distinction between "how" and "why" is an analogous one. [1] For the infants this distinction is moot.
      - gus_massa 8y ago
        A mirror has no intrinsic color. The "color" of the mirror is whatever is reflected in it from the camera point of view. If you take a photo of a mirror in a room where there is a single puntual source of light and the walls are far away, and dark to avoid reflection, the mirror will appear black in the photo. If you take a photo of a mirror in a room where there is a very diffuse source of light (like the sky, or a professional diffuse illumination equipment) the mirror will appear white (or sky blue) in the photo. --- My wife make artistic paintings and sometimes she uses shiny mirror-like materials in parts of the frame. It's difficult to take good pictures of them, because you want to make these parts appear shiny, but not too shiny. Also, you don't want too much light reflection in the normal part of the frame. So you must carefully select the angle to take the photo and the position of the lights and how puntual/diffuse they are. (Photographs of a real mirror are also difficult, if you want it to appear like a mirror. There is some reflection of light in the borders, where the glass is cut. And that reflections make it appear as a mirror instead of a plain surface.)