Green lines are fascinating

[discothefunkyhippo]

A small percentage of the population (mainly women) are tetrachromats. In other words, they have a 4th cone and can perceive more colors.

This topic was only briefly mentioned in my intro to perception science course in college, so I don't know much more on the subject. The wikipedia article on tetrachromacy mentions that "at low light intensities the rod cells may contribute to color vision, giving a small region of tetrachromacy in the color space", which could account for the phenomena that Steve mentioned. Not sure if the citation in wikipedia is accurate, but I thought it interesting.

Here is the link for you own perusal: http://en.wikipedia.org/wiki/Tetrachromacy

[absolom7691]

I have good reason to believe there are genetic differences in color vision besides color blindness.

There must be.

I am going to try this again against other colors next side by side with 520 just to see how the perception of the color changes when paired with 445, 450, 473, 632, 642.

[The_Doctor]

It gets more fun when you toss in Mesopic, photopic, and scotopic vision.

The more the merrier. I used the word advisedly.. I so hope I am a tetrachromat. I also am certain that differences in colour perception will be genetic, not just in the sense of a vision disorder. And given that 'epigenetics' is a formal aknowledgement that changing genomes only at the point of conception is a fairly stupid way for life to adapt to anything, I bet we can actually train ourselves to perceive colour, as I'm sure many artists can and do, and if persistent enough, pass on that ability to further generations, either directly, or by guiding in how to do it. Just looking at a thesaurus shows ancient words for 'red' the way Inuit have words for 'snow'. From which I go 635=vermillion, 650=scarlet, 660=crimson, 690=ruby (no surprise there...) and so forth.. But when it comes to paint swatches, I stop right there. One person's 'pale goldenrod' is another person's pee. Got to love House...

[SaltyRobot]

A small percentage of the population (mainly women) are tetrachromats. In other words, they have a 4th cone and can perceive more colors.

Is that why my wife says she needs 5 different hand bags that I call brown, but she calls tan, brown, mahogany, burnt sienna, and chocolate.

[absolom7691]

One person's 'pale goldenrod' is another person's pee.

Snagged for sig. That literally has me LOL. My co-workers were looking over my should to see what I was doing.

[The_Doctor]

Nice. I got sigged once before, said something about squid being intelligent, but I love eating them. Good, warped times. But for this latest, all credit goes to the writers of House, or whichever one came up with its original form.

[absolom7691]

I took a few more pics tonight and rediscovered how difficult it is to take decent pictures of lasers.

Context is everything. Side by side, 520 looks like a pretty bad green choice when stacked up against 532 and 543. When side by side with blue, 520 looks just as green as any of the others. Up against 473, I couldn't really see that it was 520nm that I was looking at until I brought in my 532 again. Even then, with the blue added, it looked fine. There is probably a lot more at work here but I am tired and heading off to bed. I guess this isn't such a bad color for green after all. When I get my projector finished, I'll have to get some pics of the color palette and white balance.

520, 532, and 543:


520 and 473:



520, 532 and 473:

[Galvonaut]

In hand printing of colour photographs, fine tuning of colour perception is a prerequisite. It takes a while but once you learn how to do it, it is pretty easy.

In photography we used an 18% grey card as a reference and all you should need for lasers is a standard reference white, as grey is pretty difficult with lasers. I wonder if illuminating an 18% grey card with the reference laser and the colour you want to perceive correctly would work better?

Having learnt to perceive colour using a grey card you can easily pick a neutral colour in a scene, assess whether there is a colour cast within the 'neutral' and adjust appropriately.

Photographing lasers with digital will always skew the colour. Even with film, the difference could be marked but I'm sure, much better. Even with a reference grey card in the shot illuminated with a known white colour source, digital will be more sensitive to certain colours, depending on the brand, model and settings of the camera.

I'm only just learning to photograph lasers properly and it is certainly tricky, especially with scanned and mixed RGB lasers, where shutter speed is so critical to scan speed. If anyone has any tips, they would be appreciated

Keith

[142laser]

Who here has shot a red HeNe through a green HeNe tube to make a yellow looking laser? Then use a fast shutter fior some fun in between the tubes...this can work very well. Fun...Phil

[The_Doctor]

Who here has shot a red HeNe through a green HeNe tube to make a yellow looking laser? Then use a fast shutter fior some fun in between the tubes...this can work very well. Fun...Phil

Damn! You know this might result in me risking a perfectly good HeNe tube in a very nice case now, don't you? How powerful would the red have to be though, to match 2mW of green?

Galvonaut, agreed, photos are weird. One of the hardest I remember wasn't a laser, though light colours are demanding enough, specially shortwave blues. (Deep reds aren't because they just can't be rendered on CRT or LCD monitors anyway, which is where I usually see photos now). Hardest one I did was a Peavey PC1600X MIDI controller (well worth mentioning any time in the context of music and lasering). The first one I had was purple, a strange paint, sort of metallic. It was a colour that totally defeats a CCD camera. Trying to get that faintly irridescent purple out of the dull grey-blue a camera catches took hue shifting, contrast, several things in careful sequence, and it's still not great.

For what it's worth, when I had nothing but a red diode or two, I wanted to see what glass-scattered patterns (like lumia stills) would look like if I had more lasers. I came up with this in PaintShop:
Convert to greyscale...
Diode 405 nm: Gamma 2.40,0.20,1.00; RGB -72,0,0
Argon 488 nm: Gamma 0.20,0.72,1.00; RGB -32,0,0
Argon 514 nm: Gamma 0.20,1.00,0.78; RGB -42,0,-36
DPSS 532 nm: Gamma 0.28,1.00,0.28; RGB -56,0,-64
Sodium 589 nm: Gamma 0.96,0.28,0.20; RGB 0,-32,-100
HeNe 633 nm: Gamma 1.00,0.20,0.20; RGB 0,-72,-100

If you have PaintShop or can convert scale to whatever you do have, you might get some fun out of those. The 405 was the most rewarding effort, some subtle shifts between bright and dark that are very close to the real thing (in the context of very weakly fluorescent white paint, which a lot of it is), which I only discovered a lot later when I actually had one. If enough of those colours are accurate, then they could be used to create a guide to what results to aim at in adjusting real images too. Not that it would be easy if more than one colour is present.. What may be possible is to separate to R,G,B, frames and adjust separately having first calculated intensity adjustment for the colours that most need it, then mix them back. Which is more work than I'll ever want to do.

Absolom, that rendering of 520 is as good as I've ever seen. Also, while the difference between the other two is a little bit stronger in life than it is in your picture, the character is there. My guess is just two adjustments will be enough to bring out more: saturation up by 14%, perhaps 24%, and brightness down 9% and contrast up 14% at same time, both after the saturation, not before. (Too much saturation, especially on strong contrasts, does Weird Things in Paintshop, and likely other digital tools...)

PS I have never had an 18% grey card, but it sounds like a thing worth trying. For one thing, shining lasers obliquely across a large part of its surface might be a great way to examine beam profiles. But is it 18% up from black? Or 18% down from white? Which might not be so useful for that test..