Author Topic: Looking for RGB or RGBW values of a sunrise  (Read 5984 times)

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Offline Twoflower

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Looking for RGB or RGBW values of a sunrise
« on: September 17, 2017, 07:53:12 pm »
For a small project I need a table of RGB or RGBW values over time of the sky-color from the morning just before the sun rises until the sun is nicely over the horizon**. In the end I would like to play back this using a LED strip. Actually two strips: One RGB and one white. Thus the RGBW. But I think I can convert an RGB table to RGBW.

As I don't have a single pixel RGB sensor I need to find another way. My idea so far was to setup a cam looking into a white, opaque globe to get the sky colour as whole. Do a picture every minute or so. And reduce the rescale the picture to 1x1 pixel to further obscure the light and get the RGB value from the sky from that remaining pixel.

Any other ideas, or is there somewhere an existing table I can use? An existing table would be nice as here the winter fall is coming and the chances to capture this is not that high any more.

**I'm speaking of a rising sun as seen from Earth. And a nice one is preferred ;-)
 

Offline evb149

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #1 on: September 17, 2017, 08:04:25 pm »
It depends somewhat on your altitude, latitude, meterological conditions (haze, smoke, moisture, dust, ice crystals, pollution ... in the air).  Recently there was so much smoke in the air that the sun was actually quite dim and very red-orange to the point where you could comfortably look straight at it ten minutes after sunrise.

Do that on top of some tall equatorial mountain under clear skies and you will get a very different result, whereas even on a clear fall day with the sun low in the sky in Finland you will be seeing a much different profile.

Photographers use the "white balance" and "lux" light level meter settings and values to correct for the "color temperature" (which is I think what you're looking for) and light intensity of the scene of a photograph under some conditions.  I'm sure you could probably find online tabular data of lux values and color temperature over the course of a day in some stated conditions.

For instance some values are given here, and you could interpolate:
http://www.schorsch.com/en/kbase/glossary/cct.html
https://en.wikipedia.org/wiki/Color_temperature#Categorizing_different_lighting

It is somewhat hard to "compete" with the dynamic range of intensity of the sun with artificial lighting since after all you're talking about an order of magnitude around nearly 400W-1kW/m**2 at noon on a clear day near the equator.

 

Offline Twoflower

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #2 on: September 17, 2017, 08:35:14 pm »
Thanks evb149.

As I said, I'm looking for a nice one. So a location with low particle count (including water). OK, the longitude and altitude wasn't specified. So the altitude should be about sea level (I like the reds of the rising sun). About the latitude: Here I'm probably not that picky, lets say somewhere in the range of +/-50° would be acceptable. To my understanding that mainly changes the speed of the phases and I can adjust that. The sun position should be between 8° below horizon (blue hour) and 15° above horizon (no visible reddish sky any more). Looking at all the data, couldn't be a simulation a source of this table?

Using the white balance and lux value is some kind of different scale which should be possible to transform into the requested RGBW table. But one or two values are not enough to calculate a nice transition between the points. And so far I haven't found any table that provides more than 2 or 3 values unknown how they timely relate. That's the reason why I'm looking for a higher resolution on the time axis. Probably 20 entries are enough to extrapolate the steps in between. I wouldn't complain if I can get more steps.

About the dynamic range. That's also right, I'm limited to 12bit resolution per channel. And that's plenty for my application. Probably except that the lower end might be still to bright for my taste.
 

Offline evb149

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #3 on: September 17, 2017, 09:12:10 pm »
I will make another quick comment about measuring the overall scene which could help you gather data locally since you mentioned that possibility.

It is common for the purposes of color calibration of photographic prints or other scanned images to have a printed color chart with different scales, gradients, etc. including some points which have known specific color values that have been measured by a calibrated spectrophotometer.  Then one can photograph or scan the color test chart and look at the pixel values over the specific areas on the image which had known color values.  Then one can calculate the calibration curve for one's camera or scanner or whatever based on the locally measured colors of those areas to the known values.

This could help you referring again to the concept of white balance and color temperature correction in photography.

You could do something like take a photograph of a matte white sheet of paper or if you prefer a paper with also included grey, black, and possibly colored areas on it.  You can then present that at some angle either vertical (away from the sunrise/set) or horizontal or whatever so it is receiving whatever kind of diffuse illumination from the sky, earth or whatever.  Then photograph it over time and look at the color of it versus the known colors (good photo print paper, for instance, will have a specified color profile).

Your idea about photographing the inside of an opaque globe is a good one.  In fact that is a major method how color science instrumentation measures light intensity and color independent of the spatial distribution of the source.
The device is called an integrating sphere.  It is opaque, "white", matte but also highly reflective on the inside.  Amateurs often use hollow styrofoam / polystyrene foam spheres.  For somewhat better results you can coat the inside of such a sphere or even one made from paper mache with thick layers of titatium dioxide white matte paint.
Anyway the idea is to introduce light through one aperture so that it illuminates part of the inside of the sphere and the scattering inside the sphere makes the overall surface illumination highly uniform independent of position.  Then at an angle of 90 degrees away from the source (a short tube / baffle can additionally be used if needed) there is another aperture through which the values are recorded by a sensor like a photodiode or camera.  The angular displacement and baffle is made so that no direct light from the source is seen by the sensor only scattered light so it will be uniform as seen by the sensor.  You can see online how amateurs make integrating spheres for measuring photographic systems and light sources and such.

But even with a simple sheet of opaque white paper without optical brighteners (some printer paper has fluorescent brighteners in it but matte photo paper should not)  I have used programs like photoshop to do color calibrations and measurements as well as with color test charts so that is a simple way.  If you block off the view of the ground with a baffle of course it will help in measuring the sky contribution only and as you extend that you get closer to an integrating sphere with a chosen field of view on the source side.



 

Offline evb149

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #4 on: September 17, 2017, 09:36:27 pm »
This is an interesting article somewhat similar to what you're looking for and as far as I can tell they also include the data points they used so you might process them.
In many cases though anything taken with spectrophotometric equipment (using some other model than RGB) or expressed in terms of color temperature could be converted to the RGB color system.

https://www.nature.com/articles/srep26756
https://www.cs.utah.edu/~shirley/papers/sunsky/sunsky.pdf
 
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Offline Twoflower

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #5 on: September 18, 2017, 04:41:19 pm »
Thanks again evb149.

I scanned through the papers. And that provided the right keyword in one of them: "CIE daylight model". Even if the model needs to be purchased it can be used as Google search term. Lots of interesting information pops up. Including a Daylight Visualizer from a company producing windows (free download). Probably I need to play with it to see if I can abuse it and model a integrating sphere instead a room with windows.
 

Offline ajb

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #6 on: September 18, 2017, 05:50:09 pm »
As I don't have a single pixel RGB sensor I need to find another way. My idea so far was to setup a cam looking into a white, opaque globe to get the sky colour as whole. Do a picture every minute or so. And reduce the rescale the picture to 1x1 pixel to further obscure the light and get the RGB value from the sky from that remaining pixel.

I'm not sure integrating the whole sky will get you the effect you want, since the quality of light at sunrise is highly variant depending on viewing direction.  You may get more useful information from an integrating screen aimed towards the sunrise, or perhaps multiple captures with the screen aimed at different parts of the sky.  You'll also need to be careful that the white balance of the camera is fixed through the whole capture, otherwise the changing white balance will confound your normalization process. 

Another thing to consider is that if you are looking to illuminate a room or something with your RGBW LED strips you're going to have a very difficult time replicating the way a sunrise illuminates a scene.  This is down to how the illumination spectrum interacts with the reflectance spectrum of the objects under illumination.  An object illuminated by an RGBW "orange" is going to look quite different than when illuminated by a sunrise "orange" depending on its pigmentation.  The only real way to do better here is to use more wavelengths--IE, instead of red, green, and blue, you might want deep red, red, orange, yellow, green, and blue.  Or even more--some LED stage lighting fixtures use seven different wavelengths to achieve smooth color mixing and less erratic interactions with the pigments in the scenes they illuminate. 

So if you wanted to really closely replicate the illumination of a sunrise, you'd want to take a spectrograph of the sky over the course of a sunrise and then try to match that spectrum as best you could with a handful of different wavelengths (and possibly multiple color temperatures of white as well).  It still wont' be perfect, but it will be far better than RGBW.  Of course if you're just illuminating a white screen or something, then RGBW may be just fine.
 

Offline Twoflower

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #7 on: September 18, 2017, 06:27:20 pm »
ajb: Yes you're absolutely right. The automatic setting would spoil the process. On the other side one could probably use the while balance result the Cam would use from the EXIF data. But for sure that will be the first thing I will do: Fixing the exposure settings.

And I also plan to calibrate the final setup with the same approach. Because the environment is not neutral white, but it is static. The idea is that set some specific RGBW values, taking a picture and compare what I wanted to see and what I actually get. As the equipment is very compute limited that factor will then included into the lookup table in a offline process. Unfortunately I can't fit more than 2 LED stripes into the aluminium profile. So one RGB and one White has to be sufficient. then again I don't want to have a 100% replica of a 2*10^30 kg fusion reactor shining from 150mio km through 500km gaseous molecules in my home. It would be nice to come close without getting a sunburn and the heat. But so far I need some starting point with the possibility to improve the result in a iterative process.

Unfortunately I don't have a spectrograph, just a Canon EOS 5DMk3. That's the reason for using this one to collecting the data. Plus the converting from the continuous result from the spectrograph to discrete RGBW values. But that is probably doable.
 

Offline mrpackethead

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #8 on: September 18, 2017, 07:55:22 pm »
You'll not be able to reproduce it with RGBW..  You'll need to widen the pallet out, and include Amber, Cyan and Violet LEDS as well to do it accruately.

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Offline Twoflower

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #9 on: September 18, 2017, 08:05:00 pm »
As said: I have only RGBW available. So I have to live with the area I can cover with that. Again: I don't need a full spectrum rendering. Whatever I can do with the possibilities that I can build.

In theory the driver circuit has two spare channels. But mechanically I can't add additional colours.
 

Offline evb149

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #10 on: September 19, 2017, 12:48:40 am »
If I recall what I read correctly the nature article included a mathematical model and the raw data samples were also available for download.  Furthermore the other article certainly included an analytic mathematical model and indirectly cited a bunch of datasets of which at least the Grenada one is downloadable and has some associated matlab files as well.

So although I also looked at the CIE daylight model and tangential interesting references, it appears that all that may be needed for a model (and if desired raw data sets) is included in the links above.

Thanks again evb149.

I scanned through the papers. And that provided the right keyword in one of them: "CIE daylight model". Even if the model needs to be purchased it can be used as Google search term. Lots of interesting information pops up. Including a Daylight Visualizer from a company producing windows (free download). Probably I need to play with it to see if I can abuse it and model a integrating sphere instead a room with windows.
 

Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #11 on: September 19, 2017, 04:37:33 am »
I like this idea..

However I think the use of a diffuser is going to sell you short because youll only get the average color also finding an color neutral dome sounds well nigh impossible (if there was such a thing it would either be insanely expensive, I suspect, or likely be a gel, not a dome)

The rising sun actually seems to me to at some points in time display almost all the colors of the rainbow which could be scanned in a vertical line.

But its very subtle and likely only a quite good sensor would capture it. Also, those beautiful subtle shades are right at the beginning, long before the suns disk appears.

The sun's light would fry your camera's sensor, so don't let that happen

Quote from: Twoflower on Yesterday at 13:53:12
For a small project I need a table of RGB or RGBW values over time of the sky-color from the morning just before the sun rises until the sun is nicely over the horizon**. In the end I would like to play back this using a LED strip. Actually two strips: One RGB and one white. Thus the RGBW. But I think I can convert an RGB table to RGBW.

As I don't have a single pixel RGB sensor I need to find another way. My idea so far was to setup a cam looking into a white, opaque globe to get the sky colour as whole. Do a picture every minute or so. And reduce the rescale the picture to 1x1 pixel to further obscure the light and get the RGB value from the sky from that remaining pixel.

Any other ideas, or is there somewhere an existing table I can use? An existing table would be nice as here the
winter fall is coming and the chances to capture this is not that high any more.

**I'm speaking of a rising sun as seen from Earth. And a nice one is preferred ;-)
« Last Edit: September 19, 2017, 04:40:41 am by cdev »
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Online BrianHG

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #12 on: September 19, 2017, 05:19:52 am »
You want one of these:
https://www.digikey.ca/product-detail/en/vishay-semiconductor-opto-division/VEML6040A3OG/VEML6040A3OGCT-ND/5168309
Also, you need to approximately point it upward or better in the direction away from you viewing angle to replicate the view from that direction.  Higher quality huge outdoor LED screens use them to correct their brightness & color throughout the day.  High quality cameras use them to figure out what the auto white balance should be...


« Last Edit: September 19, 2017, 05:28:08 am by BrianHG »
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Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #13 on: September 19, 2017, 06:39:44 am »
Ages ago I used to use a program called Chromatica which deconstructed an images palette in a really quite useful(for a web developer or illustrator) way.

You'll lose the potential to do something much more effective if you attempt to merge all the beautiful individual colors in a sunrise or sunset into one.
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Offline Twoflower

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #14 on: September 19, 2017, 04:55:19 pm »
Ok, now we get somewhere! I haven't expected less from the forumites  :-+

@evb149: I've seen the Matlab-code in the GitHub repository. But I didn't spend too much time in there. But the nature article and the github description mentioned that there the RAW information are hidden. It's on my to-do list to dig further in there. That looks promising.

@BrianHG: The Vishay VEML6040 colour detector looks very nice and it's cheap too. And easy to use as the whole analogue circuit is included (I'm a digital guy; for me everything between 1 and 0 is broken ;) ). Probably I'll order few as a colleague saw it and wand two as well. That would make the final calibration much easier. But I don't plan to do a closed loop. Just a one time calibration of the environment. The recording of  rising sun with this will be a piece of cake as well. I haven't expected that they are that cheap and easy to use. Except the soldering might be a small challenge. But I've managed to solder SMD devices first time right I'm not too much worried.

@cdev: Unfortunately I can't manage to find the Chromatica software. There's too much noise if you enter the name plus some other keywords.

@cdev: I thought about using individual LEDs to do something like the Philips Ambilight. But I decided against it as the stripes I plan to use have more power (RGB combined: 420lm/m, white: 2240 lm/m), higher density (RGB: 60/m, white: 140 LEDs/m), and the white a much better colour rendering (Ra > 80, not the best, but reasonable). So I decided to go down to a resolution of 1x1 pixel.

Again thank you so far for the input. Still if someone has some additional nice ideas, hints. I'm open for any input.
 

Online BrianHG

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #15 on: September 20, 2017, 01:25:52 am »
If you just wanted to replicate the white of the sun, not sky color, I have done a Planckian locus in the CIE 1960 UCS color temperature correction for my video scaler and I can give you the RGB correction factors for approx 9000K through 3000K, the sun at high noon being flat 100% RGB = 5000K and approximately being 3400K 1 hour before dusk and 1 hour after dawn.  The adjustment is close to the human eye's visual response once a reference color is converted to RGB.
IE, put an RGB color in, use the selected color temperature correction factors and get a new RGB color out.
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Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #16 on: September 20, 2017, 05:08:29 am »
You might be able to create a sunrise look with mixed dichroic light.
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Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #17 on: September 20, 2017, 05:11:44 am »
It was a Photoshop plugin for the first iteration of plugins under OS 9 mostly. The best period for plugins.
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Online rs20

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #18 on: September 20, 2017, 06:09:03 am »
Ummm, why are people suggesting RGB light sensors chip? Almost everyone has a color digital camera, and the sensor of a digital camera happens to consists of millions of RGB light sensors, pre-connected to a trivial-to-use USB / SD-card interface.

Your problem reduces to recording a video of a sunrise with a decent-quality camera, and then also record a second movie of your RGBW strips being run through a sequence of different values. The second movie is your Rosetta stone; telling you which RGBW intensities result in a given recorded value in the camera. Just apply that transform (some basic interpolation required) to find the RGBW intensities required to produce the same response in the camera as the sunset, and your RGBW strip will now produce output that looks identical to the sunset (at least as far as your camera is concerned; a crap camera may let you down here). It goes without saying, as mentioned by others, that we way the light distributes through the room will not be identical, just the average hue of light (depending on how you crop/average the recorded images.)

If you just point an SMD RGBW sensor vaguely at the horizon, you have virtually no control whether it mixes in the blue sky above or the green grass below, which would mush away the orange of the sunrise.

I did something similar once to produce an image on a computer screen that looked exactly like an apple, using a camera taking a photo of the screen to correct for the transfer functions of both the monitor and camera. I had the real apple propped up in front of the screen and it worked surprisingly well -- as in, people would be walking up to my demo from afar saying "Why do you have two apples propped up in front of a blank computer screen-- OHHH WOW". (Context: then you'd look through a hyperspectral filter and they looked totally different, ergo "look how much information your eyes are missing" etc etc.) Just a consumer digital camera and MATLAB.

Just remember that sRGB is a non-linear representation; things will be seen to be behaving much more linearly if you convert back to a linear space (e.g. Nikon RAW files are in fact just 16-bit TIFFs with linear color space.)



 

Offline Twoflower

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #19 on: September 20, 2017, 05:33:24 pm »
About the 'Sun colour' and the 'sky colour'. That's a question I had also in my mind and feared to answer. To be honest I can't give an answer here. Probably a mixture from both. As my project is actually a try to get me awake in the winter time this is probably a question I should ask in a medic-forum. The only paper I'm aware of is that the blue light seems to be problematic if you want to sleep. So probably it's a good idea to have the blue hour in the show included. I'm sure there are papers out there but I haven't looked. But as the lookup table isn't set in stone OTP-ROM. I can run some tries to see how it will eventually turn out.

Using the the RGBW sensor/Camera/Simulation I can probably tweak the opening of the viewing angle to change the ratio between full sky (180°) and more sun-whigted configuration (e.g. 20°).

@BrianHG: That sounds interesting. Maybe I'll come back later to your offer. The RGBW sensor looks very tempting and adds to my current project another one. Plus an easy way to run a room calibration.

@cdev: That dichroic filters would require a full spectrum light-source. I'm not sure is a white LED will working well enough. And would eat a lot of the light as the not used light will be reflected the other direction. The plan is to flood a roof-wall (45° angle). I'm not sure if such filters exist for a line shaped light source and probably would require motors/servos to change the colour. I've seen lamps having such filters, they look very interesting.

So probably the plug in is not available. Might have been interesting of the results.

@rs20: I started my idea with the cam approach. But it has some downsides as well.

One of the problems of a cam might be the dynamic range of a prosumer/consumer cam (like the EOS D5 Mk3 that is floating around here). Starting a the blue hour running until the sun is reasonable above the horizon is probably too much. So you need to take care there too. Not impossible but something you need to take care of.

The colour sensor would be fitted with a opaque dome. I never came to the idea to use the bare sensor. This could also reduce the environmental impact. Just limit the viewing angle to the upper part of the sky.

the demo you mentioned sounds nice. I would like to have seen it. Yes the human eye-brain combo is fascinating. The dynamic range of the eye on one side and how easy the brain can be fooled on the other side.

Thanks for the heads up with the non linearity of the standard colour system. One more reason to use the RGB sensor. You can keep the whole flow relatively controlled. The only pitfall here I see is the room-calibration. In case the LED colours don't match reasonable with the filters of the sensor. That would probably need a fall back to the white sensor channel and run the calibration for each colour channel  independent. But that probably counts also if I would use a camera for this calibration run, but with no fall-back solution.

Again thank you very much for this productive discussion.
 

Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #20 on: September 20, 2017, 08:43:52 pm »
Blue LED light all by itself should be diffused by bouncing it off of something - Blue LEDs shining at you above a certain level thats not as high as we would wish may damage the eyes.

I found lots of stuff about this on pubmed.

Interesting, other colors may have other effects.. Red light, as I am sure you know, is postulated to be better for people before they go to sleep.. I even found some tantalizing side excursions that I bookmarked but have not had the time to explore more fully..

Green light may be good for your health :) 

Its my understanding that the pineal gland is where our body's circadian rhythm is regulated.

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Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #21 on: September 20, 2017, 08:58:22 pm »
I thought you were undertaking some kind of artistic project or installation.

There is a lot of variation in sunrises and sunsets both seasonally and geographically.

If you can get a decent camera, whose color rendition you trust, you could maybe mount it in a fixed position and use it to take standardized photographs at fixed intervals. Maybe once each minute at exactly the minute. Store them in a database and then you could call it up, you could also create custom functions so you could say, get a animation which represented the same time before or after the sunrise and or sunset throughout the year. You should also bracket extensively so you can do HDR. You likely could keep a single camera very busy all the time.

That would tell you more about the colors and trends than anything else I could think of, perhaps.

You might want to take a look at the biological pathways involved in the circadian rhythm system.

I have two friends who have studied the process of wakefulness and sleep - extensively. Haven't talked to one in decades and the other is now deceased..

But its very interesting stuff.

Issues like SAD may be rooted in some amino acid imbalance.

Quote from: Twoflower on Today at 11:33:24
About the 'Sun colour' and the 'sky colour'. That's a question I had also in my mind and feared to answer. To be honest I can't give an answer here. Probably a mixture from both. As my project is actually a try to get me awake in the winter time this is probably a question I should ask in a medic-forum.
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Online rs20

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #22 on: September 21, 2017, 01:10:47 am »
The RGBW sensor looks very tempting...

Another point; I'm not sure if people are suggesting taking the 4 channels out of an RGBW and using them to drive the RGBW strips? I.e., take R reading from sensor and drive red LEDs accordingly, take W reading from sensor and drive white LEDs accordingly... Because if that's what is being suggested, that's a terrible idea. Consider what happens if you ask this system to reproduce a pure red laser. Both the R and W channels of the RGBW sensor will respond, and therefore both the Red and White LEDs in the strip will light up. But this is obviously the wrong thing to do; the best impersonation an RGBW strip can do of a red laser is to turn the red LEDs on only. Turning the white LEDs on as well would just wash out the colour.

This is why it's preferable to use some sort of basic feedback or calibration/characterisation; and once you're doing that the W channel of the sensor is of very little value.

One of the problems of a cam might be the dynamic range of a prosumer/consumer cam (like the EOS D5 Mk3 that is floating around here). Starting a the blue hour running until the sun is reasonable above the horizon is probably too much. So you need to take care there too. Not impossible but something you need to take care of.

Fixed ISO + Aperture, but leave the camera to choose a shutter speed. Check the EXIF data to compensate. Also, whether you actually want to be matching the brightness of a real sunset is questionable; I highly doubt that your LED strips can compete with direct sunlight. So you're going to want to deliberately compress your dynamic range anyway.

Thanks for the heads up with the non linearity of the standard colour system. One more reason to use the RGB sensor. You can keep the whole flow relatively controlled.

Meh, I'm suggesting just calibrating the whole RGBW strip + camera filters + RGB transform as a single black box -- that's the beauty of this approach, you don't need to tease these things apart at all.

The only pitfall here I see is the room-calibration. In case the LED colours don't match reasonable with the filters of the sensor.

No, you explicitly don't need to worry about this! That's what the calibration is for. As long as you trust that your eyes have the same response as the digital camera; everything else is sorted.

But hey, whatever floats your boat. I guess it's plausible to claim that the response of the RGB filters of the chip recommended earlier (just ignore the W honestly, it extends way too far into the NIR) are closer to that of the human eye than the filters on a typical digital camera. And there's nothing inherently wrong with using the sensor, it's just that it feels to me like a lot more work.
 

Offline cdev

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #23 on: September 21, 2017, 01:32:38 am »
Don't LEDs also work in reverse, so to speak, with their maximum sensitivity being at the color they emit light at?
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Re: Looking for RGB or RGBW values of a sunrise
« Reply #24 on: September 21, 2017, 01:45:28 am »
Don't LEDs also work in reverse, so to speak, with their maximum sensitivity being at the color they emit light at?

No, they will respond to colors at a higher energy/frequency than what they emit at -- i.e., photons with enough energy to promote electrons across the bandgap or whatever (if the LED epoxy is tinted red, though, that will obviously contribute). In any case, even if the sensitivity curve matched the emission curve perfectly, that's explicitly not what the OP wants -- the OP wants sensitivity curves that match the human eye, as creating an experience that matches a sunset (as seen by humans) is the aim of the game here.
 


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