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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Moire Issues

"We do see aliasing on stuff that moves " Can't say I've seen that myself - care to elucidate? Is that spatial (which is what I'm on about) or temporal aliassing?

Graeme
 
aliasing with the naked eye ?

aliasing with the naked eye ?

You can get temporal aliasing (rotating objects seem to stop or move backwards, etc.) if you have a fluorescent light, strobe light or any other light that turns on and off, but I don't understand how spatial aliasing (moire patterns) happens with your naked eye unless you are looking at a scene through a screen door, grille, cloth etc.

In theory, since your eye's retina is composed of discrete photosensitive sites it could have aliasing, but the rods and cones have no fixed pattern, and besides your eye is in nearly constant motion. I'm curious in what situation you could possibly see spatial aliasing.
 
And the brain has fantastic image algorithms!

Graeme
 
Graeme Nattress said:
And the brain has fantastic image algorithms!

Graeme
Click to expand...

This came to my mind the other day as I was driving along and noticed the wheels of a car in the lane next to me. Its wheels (spokes) looked like they were moving backwards, as in the same effect that you can notice on film. I wondered what our eyes' refresh rate is?

Oh, and no, the wheels in question weren't those funky spinners... :)
 
Yes, that's temporal aliassing.

The brain is funny too though, with optical illusions and the like!

Graeme
 
pixelchef said:
I wondered what our eyes' refresh rate is?
Click to expand...

I wrote a paper on this topic (or just how digital imaging compares to our eyes and brain) back in college. I researched and researched and at the time (nearly 10 years ago) there just wasn't much to be found. There is just so much about the human brain and our nervous system that is still a complete mystery. One of the most fascinating pieces of information I dug up in my research though was a study done on the human eye and color. I can't recall the details of the conducted by who and when or where. But they used cards with color gradients in red, green, blue, white to black, yellow, purple, orange, etc.. In an attempt to determine just how many shades of color the human brain could differentiate. What they found is that it varied drastically from one person to the next and results for males fell within one range and female results were in a slightly different, but identifiable range. But the general consensus was that the human eye can differentiate over 2000 shades of grey, nearly 1500 shades of red, 2000 shades of green and 1200 shades of blue. Human vision is essentially 4-channels, Red, Green Blue and Grey. ...The study also found that a small percentage of individuals (just a few percet like 2-3%) of those tested had vision ranges that shifted slightly into the infrared portion of the spectrum. These individuals tended to be more sensitive to various "fluorescent" colors and could see more tonal ranges where most people just saw something white. They also found that many people are blind or not sensitive to certain tonal ranges. So they may be able to see levels in a red gradient up to a certain point and then several spaces on the chart would appear as a solid color tone before it began to look like a gradient again. It was fascinating, but I can't recall much more than that.

Our eyes also don't have a "frame rate" But it seems that our brain samples the rods and cones within our eyes individually and in a semi-random order with the ones near the center of our eyes firing more rapidly. I don't recall ever reading anywhere as to what the actual "sampling rate" or "refresh rate" of the rods/cones in our eyes actually is... Or if anyone truly even knows.
 
Fascinating stuff, man.

I guess they'll figure it out the day we get our movies delivered straight into the optic nerve. :)
 
I'm waiting for the day I can dump my thoughts/dreams directly to physical media and edit them in real-time. :D
 
pixelchef said:
This came to my mind the other day as I was driving along and noticed the wheels of a car in the lane next to me. Its wheels (spokes) looked like they were moving backwards, as in the same effect that you can notice on film. I wondered what our eyes' refresh rate is?

Oh, and no, the wheels in question weren't those funky spinners... :)
Click to expand...

Hmm. The only time I've seen this in real life is in the dusk/evening when the strobing streetlamps will cause this. What time of day did you see this?
 
It was daytime. I thought it was odd, myself. My first brush with that effect was as a kid watching "To Fly" at the Smithsonian Air & Space Museum in the scene with the old car. Funny how things like that stay with you.
 
AppliedVisual said:
it seems that our brain samples the rods and cones within our eyes individually and in a semi-random order with the ones near the center of our eyes firing more rapidly.
Click to expand...

I think it's the opposite: the center of the eye is higher resolution/Lower sensitivity/Low refresh while the outer region is low resolution/Higher sensitivity/High refresh.

Seems to be an inherited "Hunter" feature, which aids us to detect enemies coming from the sides of our vision.
 
I've seen the reverse-spinning illusion with my own eyes here and there working with fast-spinning power tools and electric motors. I wouldn't think that car wheels would do it, but maybe they could. Perhaps it was an effect with the wheel design or spokes combined with turning at just the right speed.
 
Anders Holck said:
I think it's the opposite: the center of the eye is higher resolution/Lower sensitivity/Low refresh while the outer region is low resolution/Higher sensitivity/High refresh.
Click to expand...

Could be... I was basically trying to recall from something long ago. I do know that our eyes are higher resolution (more rods/cones) in the center vs. the outer regions. The brain does process peripheral vision differently too and we tend to easily notice motion there rather quickly, but not notice as much for color or detail.
 
spinning wheels

spinning wheels

Interesting that you bring up seeing the wheels spin "backwards". I have seen this several times, but not often, but a friend of mine said that was impossible unless it was done on film. (or digital.)

You see it in car ads a lot, and now, when I've seen it in real life I've been telling myself that I must be hallucinating again! :)

-Jerry
 
gcaussade said:
Interesting that you bring up seeing the wheels spin "backwards". I have seen this several times, but not often, but a friend of mine said that was impossible unless it was done on film. (or digital.)

You see it in car ads a lot, and now, when I've seen it in real life I've been telling myself that I must be hallucinating again! :)

-Jerry
Click to expand...

Hi Jerry,

I was wondering also how Jeff was, and now you, are seeing car wheels that appear to be rotating at a different speed then in real time. Was the sun low in the sky and streaming through a picket fence? Or was there some kind or light reflecting back and forth between the two vehicles causing a strobing action? I can see it happening in a machine shop with crappy old flourescent lighting, but on the open road? Mayby it was due to that exotic mushroom souffle or a misspent youth! LOL

Chuck
 
Kyle, let's rip it down I-15 and watch each others' wheels! Of course, we'll be at a crawl right about now, *sigh*.
 
kylemallory said:
I know I've seen this (car wheels thing in person) multiple times myself... Damn you all, now I'm going to obsess about it on the way home from the office!
Click to expand...

Is that the office you work at or the "office" we go to after work? Could make a difference.
 
Ah ha...the Beehive State Road Warrior Gang strikes again!
 
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