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On NTSC Video, Blue Blurring, Chroma Subsampling

Posted by simoniker on from the nothing-a-knock-on-the-head-won't-fix dept.

NEOGEOman writes "Something I've been fascinated with for a long time is video signals. On my website I've spent over six years collecting video and other hacks for game consoles. I've recently put together the fourth revision of my video signal primer and it's expanded to six pages now, including strange subjects like chroma subsampling, horizontal colour resolution and rather interesting revelation: your eyes suck at blue."

6 of 308 comments (clear)

  1. Suck at blue something horrid. by danamania · · Score: 4, Interesting

    My eyes suck especially badly at blue. a pure-blue image is something my eyes completely refuse to focus on. I can see the image is there, see that it's blurry, but whatever makes my eyes focus just doesn't work on blue. Light a room with pure blue light and I'm almost blind. gah!.

    Add some other colours and I'm fine. Curiously, given a red line of text, a green line of text and an off blue line of text, I have to focus differently for all three. (Fully blue is, of course, a complete waste of time :)

  2. Wow. by TheSHAD0W · · Score: 4, Interesting

    I'm red-green colorblind, and the pictures on the LEFT, with the low-resolution red images, look as good to me as the original or the one with the low-res blue. Does anyone else notice this?

  3. Even better reason... by K8Fan · · Score: 4, Interesting

    Our eyes suck at seeing blue for an even better reason - there are very few blue things that:


    1. You can eat.
    2. Can eat you.

    From an evolutionary perspective, that's the most important thing. We're get good at seeing green, because many green things are edible, and some things that want to kill us are good at hiding in green areas. So people who were especially good at seeing movement in green areas, and finding edible green things tended to survive, while those who didn't died out.

    --
    "How perfectly Goddamn delightful it all is, to be sure" Charles Crumb
  4. Re:Obvious Physics by Anonymous Coward · · Score: 5, Interesting

    You have been misled.

    It is in fact BLUE at 445nm that the eye is most sensitive to. Blue receptors are the most sensitive.
    This "sucking at blue" thing has nothing to do with sensitivity of the receptors, but with the fact that only 2% of the cone receptors are the blue sensitive ones, so you have no resolving capability in the blue part of the visible spectrum.

    This is an issue of resolution NOT sensitivity.

    Furthermore, I have been researching vision for about 10 years now, and I can tell you that the curve you linked to is totally fucked up. The leftmost curve is not far enough to the left at all. 445nm, which is what your blue cones are sensitive to is far more purple than that stupid graph would have you believe.

    You need more reputable sources.

  5. Re:Good explanation but... by NEOGEOman · · Score: 4, Interesting

    The author knows he knows nothing, but knows more than the hundreds of info-starved fanboys on forums the world over, and knows enough to put together a primer (And I'm repeating myself here) that is an introduction to a subject, not a comprehensive guide.

    Also, as far as I know no one pumps "NTSC DV" through an svideo cable, unlress they're way off spec. Svideo is analogue, not digital. Or are you using a non-spec definition of "DV"? ;)

  6. It's due to wavelengths by SirNarfsALot · · Score: 5, Interesting

    You have to focus on different colors differently because red, green, and blue light are all different wavelengths and therefore are refracted slightly differently by your eye (shorter wavelengths, i.e. blue, refract more, longer wavelengths - red - refract less). You have to focus closer in on a red light than a blue light for it to be sharp, if you can even do so.

    Something I don't understand is that blue light seems to exaggerate my mild astigmatism; I have a Logitech mouse that drives me crazy if I try to focus on the blue taillight. Red lights I can focus on quite clearly and from further away (I am also nearsighted) than any other color lights.

    Fun related trivia bit (and forgive me if this is common knowledge):
    If you have a decent old 35mm SLR camera with a normal lens (other lenses may have this too) look at the focus ring. There is a marker for where to line up the focus ring in normal conditions, and then there should also be a little red dot a fraction of an inch to the side of it to show where to line up the ring when shooting on infrared film. You have to focus the lens closer for infrared than for visible light, because longer wavelengths refract less.

    This is all related the prism rainbow effect, too.