What did you see in the sky tonight?

[Chris Peterson]

Yeah. Arguably, green has long overlapped with dark, muddy yellow. Take this painting, Nymphs and Satyr, by William Bouguereau:
http://upload.wikimedia.org/wikipedia/c ... uereau.jpg

Ask anyone at all what color those leaves are. What color are they? They're green, of course. And yet there isn't a lick of green in that painting. Not even the greenest looking leaves are green.

Point taken, to a degree. But you'd need to define "green". Certainly, there are many pixels in the green appearing sections that have a substantially greater green component than red or blue. Colors that in any Pantone booklet would be classified as greens, and which most people would call green.

Perhaps you mean there are not saturated greens?

[geckzilla]

Perhaps you mean there are not saturated greens?

No, I meant there are no greens at all. There are some very small areas of very low saturation greens. The point is that the majority of green in this image is not at all green.

[Chris Peterson]

Perhaps you mean there are not saturated greens?

No, I meant there are no greens at all. There are some very small areas of very low saturation greens. The point is that the majority of green in this image is not at all green.

Well, without a better definition of green, I'm not sure I agree with that assessment. Color is, of course, a perceptual quality, not a physical one.

[geckzilla]

Perhaps you mean there are not saturated greens?

No, I meant there are no greens at all. There are some very small areas of very low saturation greens. The point is that the majority of green in this image is not at all green.

Well, without a better definition of green, I'm not sure I agree with that assessment. Color is, of course, a perceptual quality, not a physical one.

We'll give it a broad one: Anything between pure yellow (FFFF00) and pure cyan (00FFFF). It's a little hazy when we're talking super low saturation greens but there even allowing those there are still very few in that picture.

[Chris Peterson]

Well, without a better definition of green, I'm not sure I agree with that assessment. Color is, of course, a perceptual quality, not a physical one.

We'll give it a broad one: Anything between pure yellow (FFFF00) and pure cyan (00FFFF). It's a little hazy when we're talking super low saturation greens but there even allowing those there are still very few in that picture.

I'm not sure how to interpret your definition, since it's a 3D colorspace.

I will say that I think most of the vegetation is reasonably called green. If you simply pick pixels at random in the leaves and grass, the resulting colors- in isolation- usually fall in the range that most people call green or that you'd find in the green row of paint chips at the hardware store.

[geckzilla]

I think most people, outside of context, would consider the paint chips to be "olive" colored at best and more likely brown. I have put together a picture to illustrate the color illusion.
http://geckzilla.com/stuff/bouguereau_n ... colors.jpg

[Beyond]

I think most people, outside of context, would consider the paint chips to be "olive" colored at best and more likely brown. I have put together a picture to illustrate the color illusion.
http://geckzilla.com/stuff/bouguereau_n ... colors.jpg

Once you get past the guy's really hairy legs and cloven feet... there really doesn't seem to be much green in that forest, at least not compared to the green blocks on the sides of the picture. I wonder how those green blocks would compare to my avatar picture?

[Ann]

To me, that is clearly a green landscape. There are no saturated greens there, no. Some leaves look a muddy grayish-blue, as leaves may do in a certain kind of muted light. Others are olive-green. I don't know about you, but green olives are green to me, although most definitely not a saturated green.

I remember going home on the train several years ago and looking out at the brilliantly sunlit early September landscape. And then it just struck me that the leaves of the trees were not green. Their colors were muted, as if they were coated with dust and dirt.

But the grass on the ground was a brilliant emerald green.

Ann

[geckzilla]

Would you call these colors green on their own without them being in the shape of foliage? It's really weird because if you brighten that color in the second row, second column, it's this color. It's clearly yellow to me and is one of the dominant "green" colors of that painting.

[Ann]

Would you call these colors green on their own without them being in the shape of foliage? It's really weird because if you brighten that color in the second row, second column, it's this color. It's clearly yellow to me and is one of the dominant "green" colors of that painting.

colors.jpg

Ah, but you need to brighten it to make it look yellow.

As a kid I read somewhere that red, green and blue come in oversaturated shades, when they are very dark. But yellow, said the book, is never oversaturated. Well, maybe not oversaturated, but it can sure be darkened, in which case it often looks brown. Brown, interestingly, isn't a pure hue (if I got things correctly), but a dark version of yellow or orange.

You just showed us that a darkened shade of yellow may also look green when it is darkened.

One thing that is interesting to me is that the typical green shades of vegetation are often really quite yellow-green. And that is not because they are getting sick or dried-out or assuming their fall colors or anything. That's just their natural color. Their hue is far removed from blue, but quite close to yellow.

This picture demonstrates how much yellower the leaves of a tree are compared with the color of a green traffic light.

Ann

[geckzilla]

I'm still of the opinion that most reasonable people, when color illusions and biases are removed, would say that "olive" color is indeed green. You have to calibrate your perception when looking at these things. I often find the only way I can do it is by using a color picker and looking at numerical color values.

[Chris Peterson]

Would you call these colors green on their own without them being in the shape of foliage? It's really weird because if you brighten that color in the second row, second column, it's this color. It's clearly yellow to me and is one of the dominant "green" colors of that painting.

I would consider about half of those colors to be greens by themselves. Together here, the palette is obviously a green one.

[Ron-Astro Pharmacist]

To me, half the colors may have some green mixed in but I would say this is green.

Green.jpg (5.61 KiB) Viewed 10073 times

http://science-edu.larc.nasa.gov/EDDOCS ... olors.html


What determines a bright green from dark green as we perceive it?

Prism.jpg (8.03 KiB) Viewed 10073 times

Is it its actual wavelength? For example 510 is usually identified as green. Would 515 be light green and 505 be a darker green? I saw your discussion and also wondered how subtle differences in shades, brightness, greyscale (or any of the varibles in color) affect its detected wavelength?

[Chris Peterson]

Is it its actual wavelength? For example 510 is usually identified as green. Would 515 be light green and 505 be a darker green? I saw your discussion and also wondered how subtle differences in shades, brightness, greyscale (or any of the varibles in color) affect its detected wavelength?

In nature, we seldom see colors that are spectrally pure. Usually, we see a mixture of wavelengths that our trichromic system translates to a color. Keep in mind that color also encompasses intensity (two sources with the identical spectral makeup, but different intensities, will be seen as different colors).

[Chris Peterson]

Tonight, a 25-hour new Moon setting in the evening sky.

[Nitpicker]

Tonight, a 25-hour new Moon setting in the evening sky.

That's a nice one. (If only I could see through the epic, cyclonic rain storm that is bearing down on me at the moment.)

[Chris Peterson]

That's a nice one. (If only I could see through the epic, cyclonic rain storm that is bearing down on me at the moment.)

We've got a moderate winter storm moving in. Lots of fluffy clouds right now, the sort you see before a front. I'd love to image the conjunction tonight, but I'm not optimistic of any clear skies. But right now I can still see plenty of blue between the clouds, and both the Moon and Venus are easy with binoculars, and visible (with some difficulty) to the naked eye when you know just where to look. No sign of Mars. It's just to the right of Venus, but I think it's dimmer than the sky background. Anyway, I shot this image just a few minutes ago, shortly before local noon. Moon upper right, Venus lower left. They're drawing together, so I'll keep an eye on them until the clouds are solid.

[Ann]

Lovely image, Chris!

Thick cloud cover here, by the way.

Ann

[geckzilla]

Moon, Venus, and Mars above my neighbors' houses nestled nicely between the trees.

3 exposures at F/4 1/3s 1600iso 40mm stacked for some noise reduction

[BDanielMayfield]

Moon, Venus, and Mars above my neighbors' houses nestled nicely between the trees.

Moon_Venus_Mars.jpg

Yes, my wife, driving home looking into the west just texted me

It's beautiful!

[Chris Peterson]

Truly remarkable weather we're having. Not long after I posted the daylight image above, the clouds came in and the temperature fell 20 degrees. Then it snowed all afternoon, dropping at least an inch. At about 4:30 it started clearing up. By 5:00 there wasn't a cloud to be seen, just crystal blue twilight. The storm should be back through by midnight, and we're under a storm warning until Monday morning, with expectations of 12" or more. But perfect for the conjunction tonight.

[geckzilla]

Bruce: I hope texting and driving is not a frequent habit of hers!

Chris: Lovely photo with the moon just peeking over the tree. Nice to ring in the lunar new year with such good fortune. (can you "ring in" the lunar new year?)

[Chris Peterson]

Chris: Lovely photo with the moon just peeking over the tree. Nice to ring in the lunar new year with such good fortune. (can you "ring in" the lunar new year?)

Thanks. And for the final amazing thing, I walked out of my lab after posting the image, to head up to the house, and it was snowing again, and I couldn't see anything in the whole west side of the sky, and just a few bright stars to the east, quickly fading. Unbelievable timing.

[BDanielMayfield]

Bruce: I hope texting and driving is not a frequent habit of hers!

She uses the speaker function to do the typing. Plus, she had just got into my truck and wasn't even moving yet.

[geckzilla]

Bruce: I hope texting and driving is not a frequent habit of hers!

She uses the speaker function to do the typing. Plus, she had just got into my truck and wasn't even moving yet.

Better, but you both may want to reconsider whether it's really necessary to use the phone while driving, even hands-free.
http://www.cmu.edu/news/archive/2008/Ma ... ning.shtml

It'd be nice if we had robot cars!