Author Topic: Looking for RGB or RGBW values of a sunrise  (Read 13843 times)

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Offline TwoflowerTopic starter

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #25 on: September 21, 2017, 05:51:23 pm »
Sorry if my simple description from the first post was misleading. A as good as I can manage with the RGBW sources is good enough for me.

@cdev: No worries about looking direct into the LEDs. It's behind my bed and cowered with a opaque diffusor.

Wrt different sunrises at different locations. That's actually one additional plus for the sensor: It's easy movable and I can ask someone who travels at a nice place to do the recording.

Yes I could use my camera in HDR or do some additional calculation to compensate changes of the exposure time (I would keep the diaphragm fixed). But I feel that this is rather cumbersome setup; especially as my tripod is a heavy load (Manfrotto) and I don't own a car.

@rs20: About the usage of the white channel: Thanks for the heads up. It would be very obvious to get completely overblown rendering of the record. That needs to be taken care of. I noticed that extreme wide range of the W channel too. I think ill still record it and keep the data but not use it.

I think a mismatch of the Filters and the LED colour might be bad. Just imagine the red LED is shifted compared to the sensor that only 20% passes the filter the RGBW sensor: The reading will be much to low and you would think you need to beef up the R channel more than necessary.

I see the sensor like a small project. For both the Cam and the Sensor I need the hardware setup (opaque dome or reflector, ...) the calculation from the sensor/cam needs to be done. Here the sensor gains a bit as I have already the RAW data in a nice format. And I have several controllers flying around which are currently waiting to be used.

@BrianHG: Probably I'l use one sensor which is used for both usage models. As I don't plan to compensate changes on the room I do a single calibration run to identify correction curves that are applied to the RAW sensor data on a PC. the processor might have enough CPU power to do this online. But imagine something red falls on the sensor and you will wake up under a green-blue sky :-DD

The pinhole lens sound like a good idea! Worth a try.

@reen flash: (OK, that's not a user rather a topic) I've watched so many sunsets over the sea and never was lucky to see one. I was aware of this effect and hoped so many times.

To my understanding a place with a view over the sea will do. And the weather conditions must be perfect: The sky must be clear and the right temperature conditions over several air layers must help to bend the light a bit around the earth surface.

I'm not sure if a plane is helpful. So far I only saw pictures from it on sea level.

Just for your entertainment I've added two pictures of the driver (6+1 12bit PWM channel, the MOSFETs are bottom side mounted, controller not mounted) and the LED stripes loosely placed in the profile with the opaque cover.

Edit: Added Pictures
« Last Edit: September 21, 2017, 06:30:58 pm by Twoflower »
 

Online BrianHG

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #26 on: September 22, 2017, 12:30:54 am »
@BrianHG: Probably I'l use one sensor which is used for both usage models. As I don't plan to compensate changes on the room I do a single calibration run to identify correction curves that are applied to the RAW sensor data on a PC. the processor might have enough CPU power to do this online. But imagine something red falls on the sensor and you will wake up under a green-blue sky :-DD

The pinhole lens sound like a good idea! Worth a try.

As for the pinhole lens, you can safely point this instrument directly at the sun and it wont fry the sensor + the distance between the pinhole and the RGBW sensor controls the field of view the sensor sees of the sky.  Like a zoom control, but, no focusing needed.  IE, the further away from the RGBW sensor, the more narrow section of the sky falls on the sensor.  The closer to the sensor, more of the sky's view-able area will be centered on the sensor.

 

Offline rs20

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #27 on: September 22, 2017, 12:48:16 am »
I think a mismatch of the Filters and the LED colour might be bad. Just imagine the red LED is shifted compared to the sensor that only 20% passes the filter the RGBW sensor: The reading will be much to low and you would think you need to beef up the R channel more than necessary.

The already-stated assumption is that the Red filter in the RGB sensor has the same response as the corresponding cones in the eyes. So, if the red LED is "shifted" such that only 20% passes the red filter, then that red LED only produces a 20% (proportionally speaking) response in the red cone, and it's exactly the right thing to do to beef up the R channel accordingly.

Meanwhile, matching the filter to the emission spectrum of the LED leaves your overall system completely blind to the fact that this LED only weakly stimulates your eye's red cones, producing far too little red light accordingly. Matching the filter to the LED instead of matching the filter to the eye is exactly the wrong thing to do.

The only issue that can be caused by a poor choice of LEDs is if the combination doesn't have a wide enough gamut. But since sunrises are not particularly saturated in colour (all the wavelengths are there in some quantity), I seriously doubt you'll run into gamut issues. (You'll know you've run into a gamut issue if your interpolation software turns into extrapolation software and requests a negative drive for one of your LEDs.)
« Last Edit: September 22, 2017, 12:56:42 am by rs20 »
 

Offline TwoflowerTopic starter

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #28 on: September 22, 2017, 06:57:51 pm »
@BrianHG: Right that distance might work as zoom. But I think as the sensor is very small this will end up in a huge 'crop factor'. Probably useful distances are in the mm range. But worth a try.

@rs20: Yes you're probably right as the sensor is designed to match the human eye. I missed that fact and just thought the total luminosity. So if the the LED has a strange centre wavelength the eye will be affected similar to the sensor. This should cancel it out. I checked the LED vs. Sensor wavelength. They're not that far away that this actually matter for my needs (620 vs 650nm, 520 vs 550nm and 465 vs 450nm).
 

Offline rocketscienceguy

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #29 on: July 07, 2020, 06:12:07 pm »
I'm also looking for an RGB sequence of a sunrise, or, preferably, a daylight cycle.  It does not need to be as precise as this original thread author intended, just an approximation for a cycle I can use as a translucent image overlay to broadly simulate day/night cycle in a game.  I've read through all the postings on this thread, and it looks helpful to someone who wants to produce their own accurate and precise measurements for a particular time and place.  No generic sequences were actually given, and I'm hoping that with my relaxed requirements someone would share such a sequence knowing it would be helpful. 

Minus a chart, I'll start experimenting with sequences.  My first thought is to start from black, and then plot a path mostly along the edge of the RGB color cube: black(255,255,255)->magenta(255, 0, 255)->red(255, 0, 0)->yellow(255,255,0)-[diagonal from yellow to cyan, bypassing green]->cyan(0,255,255).  I'd step through all the states between each of these vertices in a straight line, and, upon reaching the endpoint, I'd reverse the sequence.
 

Offline tooki

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #30 on: July 07, 2020, 06:26:55 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 ;-)
What makes you think that every sunrise is the same?

Honestly, I don’t see the point in attempting to scientifically capture something that is so wildly variable. Just play around with values until you get the desired effect.
 

Offline TwoflowerTopic starter

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #31 on: July 07, 2020, 06:52:59 pm »
I never claimed that all sunrises are the same. I was looking for a base-point to start of the tweaking you suggested. Especially what color do one would take: The color of the sun, the color of the sky (close to the sun, opposite, ...) a mixture of all. And also was looking for suggestions if either something like a dataset is available, a simulation tool or how to record the color composition. And I got very valuable feedback from the forumites (big thanks about that).

I get every time surprised if there are implied suggestions that I want to do that scientifically correct**. I just want to re-build a kind of Phillips sunrise alarm clock. Nothing more, nothing less :-)

Unfortunately the project got pushed out even further :-(


** In the meantime I was visiting the PTB here in Germany. They have a scientific setup for testing solar-cells. I forgot how many different wavelengths they use. I have only a picture taken of the big setup: 1018712-0 they had also a smaller but more accurate testbench.
 

Offline TwoflowerTopic starter

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #32 on: September 26, 2020, 01:50:53 pm »
To provide some additional input: The latest version of the render software Blender (free&open source) includes a physically based sky renderer called Nishita (a bit down is a short demo reel including the source files for that setup). The code behind is documented here.

The result looks impressive and might be a reasonable good source of daylight color transitions. Especially you can replay and modify it as you need not like using a real world measurement.
 

Online macboy

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #33 on: September 28, 2020, 09:10:21 pm »
Colour is funny business. By funny I mean extremely complicated.
You ask for RGB values. You can't just take RGB values and drive the R, G, and B portions of the LED strip to those brightnesses and expect to get the same colour. No way. Because.. what is Red or Green or Blue? The actual specific color coordinates of those primary colours produced by your strip will not match any standard. Then there is the brightness of those primary colours produced by the strip.

So even if you can convert from same arbitrary standard to something you can directly program into the strip, you have another significant problem. The R, G, and B LEDs each produce a very narrow spectrum of colors. For a display device (something meant to be viewed directly, like a TV or monitor) this can be highly desirable as it allows a wide gamut of colour to be produced. A property of the human eye called metamerism allows this spiky, uneven spectrum to appear exactly the same as any other different spectrum which happens to excite the eye's three types of cones in the same proportions. However, for a illumination source (something meant to illuminate other objects like a light bulb) this is highly undesirable, as not all wavelengths are represented in the output. Brightly coloured objects are especially affected. So while you can calibrate and tweak the LED strip to mimic any colour exactly, for direct viewing, as soon as you bounce that light off some other non-white object, it will look very different. Not even close.  This includes the paint on your walls and your furniture, your skin, and everything else in the room. It will look strange.
 
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Offline TwoflowerTopic starter

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Re: Looking for RGB or RGBW values of a sunrise
« Reply #34 on: September 29, 2020, 07:12:46 am »
Yes, there's lot of things to do to get a reasonable output. Just for the LOLs I fed the 'RAW' data taken from a set of frames to the LEDs made me wonder if I mixed up the the channels ;-). The white channels doesn't simplify things either but will hopefully improve the result as it does not have this extreme RGB-peaking. I hope to use the VEML6040A3OG color sensor to find the right relationship between the individual channels, tweak the whitepoint to get close enough to my goal. At least I think driving the LEDs with PWM provides reasonable good linearity to not run a full calibration process. And of course the setting is valid for the same type of LED combination.

The light-strip will facing a wall*. No direct light. The problem with direct light to colored objects are not given. At least as close as it doesn't hurt the eye. And the plan is to use the RGB channels only to 'tweak' the whitepoint (not correct therms, but I think you understand what I mean) to the right direction. That reduces the peaking of the RGB channels to the minimum.

*) Which is unfortunately not white but a light yellow/orangish color. So probably a final tuning is needed in the end.
 


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