General > General Technical Chat
Looking for RGB or RGBW values of a sunrise
Twoflower:
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.
BrianHG:
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.
cdev:
You might be able to create a sunrise look with mixed dichroic light.
cdev:
It was a Photoshop plugin for the first iteration of plugins under OS 9 mostly. The best period for plugins.
rs20:
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.)
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