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Old 20th November 2012, 03:05 AM   #111
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This is what PWM does to digital cameras.
Click the image to open in full size.

As soon as they fix this I'm onboard.
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Old 20th November 2012, 01:29 PM   #112
AR2 is offline AR2  United States
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Originally Posted by Pano View Post
Yes, violet - how do we see it? And why is it often confused with purple?
There isn't much agreement on the subject, just lots of arguing, audio style.
But if you dig around the digital photography forums you'll find the problem pops up often, violet objects that photograph as blue - flowers frequently.

It's interesting but I've not seen a clear answer yet. I'd welcome any info you might have.
He, he, he Pano - here you could have as much as you want of purple and violet:
Purple - Wikipedia, the free encyclopedia

I think you question needs defining on how we see, or how we capture or how we reproduce, and how we reproduce has to be divided on where - screen or color photo print which is RGB reproduction or CMYK reproduction / print? All of these will skew in certain direction and in some cases shift could be dramatical.
On how we see depends very much on what are we looking at, which is proportion of absorption and reflection which is material and pigment dependent. Certain dies are very critical, particularly the ones that are created with artificial UV protections - the most common are materials for outdoor use such as luggage or outdoor furniture. They appear as one color, but they completely shift when captured ether on film or on digital. Out of those materials what is seen as pure black, when captured shift ether to magenta or to green.

As for the digital cameras, with CCD chips they are all hypersensitive on IR and red parts of spectrum. That is why they all have Cyan type of filter over the chip. In early days of digital that was separate filter placed in front or behind the lens. In very early days it was dychroic filter that caused color shifts when used on view cameras while tilting or swinging lens. Later that filter was corrected and it was installed permanently over the chip as a part of the digital chip/back. The existence of that filter produced file that is always, and still is, low in red color reproduction. This unbalance is corrected by color sync profile specific to the hardware used. In audio term file is equalized, by creating the opposite curve.

So that is first factor to consider in conversation why something is shifted in certain direction. The next factor is reproduction on screen or on paper. RGB will always reproduce much wider color gamut, as long as we are not using moronic Microsoft sRGB profile. This profile, created to equalize viewing on any screen, will dramatically map / shift particular vibrant colors to their neighbors, such as purples to blues, or violet to reds or magentas.

The same stands for CMYK printing that will further compress color gamut, and any time that is done, it will further map out certain colors. The ones that first go are the ones that are strong in saturations. In audio terms, color reproduction suffers as well as from compression. Add to that bad or wrong color sync profile used, and both purples and violets are gone.

Next is under what viewing and lighting condition we are observing proofs. Some paper and inks for inkjet proofers are very sensitive to lighting source and amount of UV component. That will further create another shift for some colors...

After we consider all mentioned variables, very often it is miracle that any color comes correct. And they do not. Even with all conditions perfect, color correction in post is very much needed to correct for all variables. The only way I consider closely matching to particular color is by measuring original material, and matching that in the post to the very reading by RGB / CMYK numbers. Arguing over color reproduction is the same arguing over audio reproduction, hahaha.
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Old 20th November 2012, 03:06 PM   #113
wwenze is offline wwenze  Singapore
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Originally Posted by freax View Post
This is what PWM does to digital cameras.
Click the image to open in full size.

As soon as they fix this I'm onboard.
They probably did, my previous workplace has LED tubes for lightning and I've snapped a few pictures with a point-and-shoot, never seen anything of that sort.

Can be solved with more LC filter anyway, both for better light quality, and to pass EMC regulation.

Add: Considering that the entire office is covered by T8 LED tubes, if each tube is a least bit noticeable it would make for some impressive intermodulation effect.

Last edited by wwenze; 20th November 2012 at 03:15 PM.
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Old 20th November 2012, 03:54 PM   #114
Pano is offline Pano  United States
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Originally Posted by Wavebourn View Post
Green color, for example, can be really green, or a mix of blue and yellow that fools imagination as if it is real green.
No, it's not fooling the imagination, if you mix yellow and blue pigments (or yellow and cyan) then they will absorb all colors but green. Thus you see green. That's how subtractive color works.

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He, he, he Pano - here you could have as much as you want of purple and violet:
Thanks for the link, I'll study it. It's great that there is more and more info on the interwebs these days.

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In early days of digital that was separate filter placed in front or behind the lens.
Yes, that's what I did with my Phase Linear 4x5 scanning digital camera back (~108 megapixel). IR filter on the back of the lens. I was trying to build RGB LED lighting banks for it, as the IR filter would no longer be needed. Pure colors would have other advantages, too. No IR or UV to excite some paint pigments that do weird things to the scans. Ultramarine is notorious.

Years ago we made an IR video camera by removing the filter on the chip. Worked great! The colors were strange, but it was fun. It was used in a kennel to see what the dogs were doing at night.


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So that is first factor to consider in conversation why something is shifted in certain direction. The next factor is reproduction on screen or on paper. RGB will always reproduce much wider color gamut, as long as we are not using moronic Microsoft sRGB profile. This profile, created to equalize viewing on any screen, will dramatically map / shift particular vibrant colors to their neighbors, such as purples to blues, or violet to reds or magentas.
Hmmm.... yeah, true enough. Color mapping in the camera and display could account for a lot of that color shift. But I think that the color filters in the camera and display device are also to blame. If the blue filter is cut to cover blue and violet, blue is all the camera will ever see. To the filter and sensor, they are the same color. Without a dedicated short wavelength filter (violet) or some other means like the eye must have, there is no way that the camera can tell blue from violet. Both excite the same sensor. I've played around with this using blue, violet and UV LEDs.

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Next is under what viewing and lighting condition we are observing proofs. Some paper and inks for inkjet proofers are very sensitive to lighting source and amount of UV component. That will further create another shift for some colors...
Yes, metamerism. A big deal in the print industry. We actually had some very cool little stickers that would show stripes if viewed under non standard lighting. They warned that if you see the stripes, lightening is not standard. Ever see those?
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Arguing over color reproduction is the same arguing over audio reproduction, hahaha.
It sure is!
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Old 20th November 2012, 06:35 PM   #115
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Originally Posted by Pano View Post
No, it's not fooling the imagination, if you mix yellow and blue pigments (or yellow and cyan) then they will absorb all colors but green. Thus you see green. That's how subtractive color works.
What about fluorescent paints?
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Old 20th November 2012, 07:09 PM   #116
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No, it's not fooling the imagination, if you mix yellow and blue pigments (or yellow and cyan) then they will absorb all colors but green. Thus you see green. That's how subtractive color works.
It's a little bit more complicated than just the difference between additive and subtractive colours.

Not that what you have said is untrue, but you can have a spectral colour, green (coloured light), which is monochromatic, or you can achieve the same impression in the brain by the combination of blue and yellow additive metamers (monochromatic coloured lights).
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Old 20th November 2012, 07:22 PM   #117
Pano is offline Pano  United States
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CC, yes I agree. I was just trying to keep it simple. Will monochromatic blue and yellow lights combine to green? I'll have to try that.
Since there are no real yellow sensors in the eye, we must see it as green and red sensors both lit up.

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What about fluorescent paints?
They actually produce light (as I understand it) and so appear much brighter than ordinary pigments - because they really are brighter. They don't just absorb, they also produce light. Or at least convert UV to some visible wavelength. It's a pretty cool trick.
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Old 20th November 2012, 07:25 PM   #118
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Originally Posted by counter culture View Post
Not that what you have said is untrue, but you can have a spectral colour, green (coloured light), which is monochromatic, or you can achieve the same impression in the brain by the combination of blue and yellow additive metamers (monochromatic coloured lights).
Exactly. That means "fooling imagination" as if the color is monochromatic. That's why it s so difficult to fool imagination completely by capturing and reproducing using selective electronic devices. And that's why incandescent lamps will be always preferable for health and arts than artificial lighting that re-creates as if white light by few narrow strips.
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Old 20th November 2012, 07:28 PM   #119
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It depends on how narrow, or the Q of the light strips. I do find continuous spectrum lights to look much better and more natural.
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Old 20th November 2012, 07:29 PM   #120
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Will monochromatic blue and yellow lights combine to green? I'll have to try that.
They do that just fine. I have a nice Christmas light string made by GE, I bought it in Costco. It does that just fine. Like my Epson projector that I use to watch movies.

But it does not mean that LED lights completely replace incandescent lamps
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