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Thread: Dimming curve question

  1. #11
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    Default Re: Dimming curve question

    Thanks Joe....that's helpful. I am starting to get my arms around the non linear piece of this puzzle. I think functionally and I suppose that nudges me in the direction of linear thought. Too much time spent in the military following those accursed checklists maybe!

    I know you jet jocks had checklists too but you guys didn't always have time to reference them which is a good 'thang' when you're traveling mach +

    Anyhow I had them force fed to me and I learned to rely on a step by step approach and was 'trained' to be dumb as a bag of rocks and to not get inquisitive and get out of the sandbox.

    That haunts me in this hobby, let me tell ya.....

    I really liked your analogy on old TV technology....in a former life I used to repair TVs and in those days we had to degausse and set screen intensity levels to get the RGB guns in the CRT balanced.... I can't tell you the number of sets I readjusted after the owner had set his own screen levels! Maybe that's where I got the obsession to balance colors from!

    I'll take your advice and not hurt my head over this issue....It would appear it is beyond our current capability.

    Quote Originally Posted by JHinkle View Post
    You keep talking as if the world is linear -- it is NOT.


    The world is one big non-linear mess and little old you is trying his best to make it fit into a linear one ... don't try too hard -- you will get a head ache

  2. #12
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    Default Re: Dimming curve question

    Quote Originally Posted by gadgetsmith View Post

    I can see what your doing with the r g b dimming curves, but is that messing you up when you try and make something white? The r g b might be a different mix than the blend you get from your dimming curves?
    It doesn't seem to.....I get a bright (pure) white and not some off white like warm white.....I don't know if the dimming curves are influencing the color of my white but I do wonder if the dimming curve still works when white is involved...and if it does wouldn't it make sense that an equal blend (brightness) of all 3 colors would by definition make pure white? Otherwise the green which is apparently so strong based on the post above would be giving me a greenish 'flavor' tint wouldn't it?

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  4. #13
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    Default Re: Dimming curve question

    If you do photography, I found for vidwo on pixels are best worked backwards. Are there any incandescent fixtures in the display? Mixing color temperrature will make most LED displays appear cold and blue completely lacking in red. The Pure wite is a cold cool white fluroscent color.

    How this applies is to use a digital camera and set it for a color temperature of your reference white. In one of the LED strings I use, white to match white is 256 red,50 green and 20 blue. Cutting way back on green and blue stopped the washout and made the string match traditional mini lights even in red. Hope this helps.
    Last edited by Technician; 05-12-2015 at 01:00 AM.

  5. #14
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    Default Re: Dimming curve question

    Quote Originally Posted by Santacarl View Post
    It doesn't seem to.....I get a bright (pure) white and not some off white like warm white.....I don't know if the dimming curves are influencing the color of my white but I do wonder if the dimming curve still works when white is involved...
    Not sure there. Joe can probably tell you if curves are applied when white is selected as a color. Even then the curves you've made to make R G and B more similar in brightness may make no difference at all when making white.

    and if it does wouldn't it make sense that an equal blend (brightness) of all 3 colors would by definition make pure white? Otherwise the green which is apparently so strong based on the post above would be giving me a greenish 'flavor' tint wouldn't it?
    Remember, white is not a color, it's an interpretation from our brain from the three cones in the back of our eyes. These three types of cones respond to wavelengths of light at (you guessed it) the red, green and blue spectrum, but they do so at different levels. For arguments sake, we can call R,G,B of 255, 255, 255 "pure white". Of course this doesn't really mean anything until you define the wavelengths of R G and B that you are producing, and in what intensities they are emitting at. Then they need to be compared to the levels of how the eye reacts to each of those wavelengths and intensities.

    In our hobby, dimming and changing RGB outputs using some form of PWM (WS2811 chip for example), creates changes in voltage, current, and junction temperature, all of which effect the spectrum of light an LED will produce. We know we can't just put in 128,128,128 and expect to get the same white at 1/2 the intensity of 255,255,255.

    As a very practical example, look at the values of R,G,B that Technician has given for his LED white to imitate a white incandescent light. 256, 50, and 20.


    Here is some literature you might find interesting. I'm by no means an expert, but understand some of the relationships that exist with light, led's and how they all intermingle regarding our devices.

    http://www.physicsclassroom.com/clas...Eye-s-Response

    http://light-measurement.com/spectra...tivity-of-eye/

    http://www.beercolor.com/color_basics1.htm (yup. color of beer. you simply can't argue the information from this website! lol.)

  6. #15
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    Default Re: Dimming curve question

    Washed out color got me to thinking from my old tv repair days as video systems are not linear. Pixel dimming is linear as they are PWM directly to their DMX value. For more info on the curves for correcting for the non linear video to properly display it, a google search on Gamma Correction may be helpful. I'm including a link to a Wikipedia article on the subject.
    http://en.wikipedia.org/wiki/Gamma_correction

    The diffeerence between brightness between pixels and a CRT disply is shown in the graph below.
    600px-GammaFunctionGraph.svg.png

    Using a Gamma Correction for your video will drastically darken the majority of the videw resulting in less washout and vivid color. while preserviing peak white.
    Last edited by Technician; 05-12-2015 at 11:59 AM.

  7. #16
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    Default Re: Dimming curve question

    Quote Originally Posted by Technician View Post
    Washed out color got me to thinking from my old tv repair days as video systems are not linear. Pixel dimming is linear as they are PWM directly to their DMX value. For more info on the curves for correcting for the non linear video to properly display it, a google search on Gamma Correction may be helpful. I'm including a link to a Wikipedia article on the subject.
    http://en.wikipedia.org/wiki/Gamma_correction

    The diffeerence between brightness between pixels and a CRT disply is shown in the graph below.
    600px-GammaFunctionGraph.svg.png

    Using a Gamma Correction for your video will drastically darken the majority of the videw resulting in less washout and vivid color. while preserviing peak white.
    Gamma correction....yikes....that sounds pretty overwhelming.... How does one go about adjusting the gamma and is more or less a trial and error process?

  8. #17
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    Default Re: Dimming curve question

    Quote Originally Posted by Technician View Post
    If you do photography, I found for vidwo on pixels are best worked backwards. Are there any incandescent fixtures in the display? Mixing color temperrature will make most LED displays appear cold and blue completely lacking in red. The Pure wite is a cold cool white fluroscent color.

    How this applies is to use a digital camera and set it for a color temperature of your reference white. In one of the LED strings I use, white to match white is 256 red,50 green and 20 blue. Cutting way back on green and blue stopped the washout and made the string match traditional mini lights even in red. Hope this helps.
    No incadescents....everything is LED and pixel..... So how do you "set a digital camera for a color temperature"? I don't take a lot of pictures of the display because the never come out looking good.....poor color quality usually...

  9. #18
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    Default Re: Dimming curve question

    To take good pictures of lights requires all manual camera settings. Auto will see most of the scene as dark and try to adjust for it blowing out the lights. As stated most LED lights are not color balanced for incandescent replacement. Under very low light most auto settings on cameras assume fireworks, candles, incandescent light sources so photos tend to severly lack red. Start with a manual light source setting of fluroscent cool white or daylight.

    If your camera has a manual white balance setting, turn on a box or pile of pixels all white and use that as the white reference to set color balance.

    If your camera has a histogram view, learn how to use it for setting exposure so lights are not overexposed.

    Adjusting Gamma for video on a matrix involves either setting dimmer curves, or using a video editor to change the gamma of the video to play on a Linear display. Either will work. This will return the video to looking more normal instead of bright advertising sign video.
    Last edited by Technician; 05-13-2015 at 02:27 AM.

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