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Thread: Is there such a thing ...

  1. #1
    Curmudgeon in Training Ma3rk's Avatar
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    Is there such a thing ...

    as a Virtual Light/ColorTemp meter? Can't call it a Digital Lightmeter as we know those exist, but I mean something to actually get specific lighting info in virtual 3D space in realtime. So much of what goes on in 3D is dependent on textures as well as lighting but at this point we've only a visual feedback of how those work together. But it's somewhat of a guessing game when it comes to trying to work with lighting ratios, particularly when trying to take GI into account.

    In the real world, we use incident meters as they are independent of what is getting lit. We can read the direct light and also what's getting "kicked" back thanks to radiosity and other light sources, & we adjust accordingly. We no longer have the gamut limitation of physical film, but there are still aesthetic considerations. Seems like there must be some means of obtaining a virtual equivalent here in the 21st century.

    I know I wouldn't mind having such a tool & that there are some really clever folk around here that dabble in such things.
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    I am confused what you actually want.

    Do you want node which is converting color input to temperature in Kelvins and output it as scalar?

    "but I mean something to actually get specific lighting info in virtual 3D space in realtime"

    ...or color temperature picker where you hover some pixel on rendered image/VPR to get temperature?

    HSB color space has Hue in range 0...360, right.
    So take a look which temperatures correspond to which color on Wikipedia.

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    In the real world, white color is just mixture of photons with various energies/frequencies/wavelengths. They can be separated by e.g. prism, or other interaction with the medium or material. From mixture of such photons it's possible to get temperature in K (where is peak of photons).
    In the (current) 3D visualizations it's all fake.

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    Curmudgeon in Training Ma3rk's Avatar
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    Quote Originally Posted by Sensei View Post
    I am confused what you actually want.

    Do you want node which is converting color input to temperature in Kelvins and output it as scalar?

    "but I mean something to actually get specific lighting info in virtual 3D space in realtime"

    ...or color temperature picker where you hover some pixel on rendered image/VPR to get temperature?

    HSB color space has Hue in range 0...360, right.
    So take a look which temperatures correspond to which color on Wikipedia.
    Not quite.

    What would be nice is is a widget that's a half sphere dome like a real light meter, that I can place in the scene (as a gaffer would do), aim at the various sources & have it record a readout in lumens or foot-candles, or whatever units I chose plus accumulative color "temp" from that direction as well, & that could store 2-3 readings. In Lightwave, after you've taken the readings such as Key, Fill and Back, it would present a grid showing color swatches and intensity level values.

    That make sense?

    Think along these lines:

    https://www.amazon.com/dp/B01L7K3HN8...g=omnideals-20
    Last edited by Ma3rk; 05-15-2019 at 12:45 AM.
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    You say "in realtime".. what does it mean in 3D? Tool working in viewport? "widget" suggests interactive tool working in Layout viewport, which can be moved by user.

    In the real world, photons flies back and forth, between active light sources, then they are reflected, refracted, diffused, and so on. They fly through room or whatever else, all the time, so they can be caught by device measuring their properties.

    In 3D world, there is no photons flying in the scene. There is light source with 2x 3d vectors: position and direction (3d vector is 3x scalar floating point, two such are 6x floats). There is target spot world position, with normal vector (and again 6x floats).
    To be able tell amount of light at "widget" location, such tool would have to do everything what does entire F9/VPR renderer. i.e. send rays in the all directions ("backward ray-tracing"), in really large amount, to get info where are geometries, then calculate surfacing and direct ("forward ray-tracing") and indirect ("backward ray-tracing") lighting reaching them, and recursively repeat it..
    ..and all this to get 3x floats i.e. single color RGB format..

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  7. #7
    Curmudgeon in Training Ma3rk's Avatar
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    Quote Originally Posted by Sensei View Post
    You say "in realtime".. what does it mean in 3D? Tool working in viewport? "widget" suggests interactive tool working in Layout viewport, which can be moved by user.

    In the real world, photons flies back and forth, between active light sources, then they are reflected, refracted, diffused, and so on. They fly through room or whatever else, all the time, so they can be caught by device measuring their properties.

    In 3D world, there is no photons flying in the scene. There is light source with 2x 3d vectors: position and direction (3d vector is 3x scalar floating point, two such are 6x floats). There is target spot world position, with normal vector (and again 6x floats).
    To be able tell amount of light at "widget" location, such tool would have to do everything what does entire F9/VPR renderer. i.e. send rays in the all directions ("backward ray-tracing"), in really large amount, to get info where are geometries, then calculate surfacing and direct ("forward ray-tracing") and indirect ("backward ray-tracing") lighting reaching them, and recursively repeat it..
    ..and all this to get 3x floats i.e. single color RGB format..
    I never said it would be easy.

    But it's not having to render or resolve anything like textures. It's just gathering the basic info that VPR uses in it's initial evaluation, so that would be the "realtime'".

    - - - Updated - - -

    Quote Originally Posted by gar26lw View Post
    Not quite. Looking for a tool to use in any scene rather than a separate scene.
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  8. #8
    Goes bump in the night RebelHill's Avatar
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    Render something and look at the value of a given pixel (in linear, float ofc)... that IS a "lightmeter" reading of that spot, this is (roughly speaking) all a renderer is. You say it wouldnt have to render anything, or sample any textures... but it would, because to trace the light values back to their source, woud be identical to rendering them for that spot.

    Basically, what you're asking for is a singe pixel limited region render.
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  9. #9
    Curmudgeon in Training Ma3rk's Avatar
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    Quote Originally Posted by RebelHill View Post
    Render something and look at the value of a given pixel (in linear, float ofc)... that IS a "lightmeter" reading of that spot, this is (roughly speaking) all a renderer is. You say it wouldnt have to render anything, or sample any textures... but it would, because to trace the light values back to their source, woud be identical to rendering them for that spot.

    Basically, what you're asking for is a singe pixel limited region render.
    Probably wrong choice of terms. All I'm looking for is intensity & color. When a VPR view initially updates for example, isn't it just getting that basic info for its starting point in the first few seconds? I guess I'm trying to tap into that information. That make sense?
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    Quote Originally Posted by Ma3rk View Post
    But it's not having to render or resolve anything like textures.
    Textures contribute to illumination of scene, if GI is turned on (nowadays people keep rendering in GI-only)..

  11. #11
    Goes bump in the night RebelHill's Avatar
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    Quote Originally Posted by Ma3rk View Post
    All I'm looking for is intensity & color. When a VPR view initially updates for example, isn't it just getting that basic info for its starting point in the first few seconds?
    No... intensity and colour IS the result of the render. The "basic info" the render gathers at its start its just stuff like the position of geometry, light positions, etc... To figure out how much light reaches a certain point of geometry... that's raytracing. Finding the colour of that point under said illumination, thats texture/surface sampling.

    Imagine the real world analogy you're thinking of... If you took a light meter and "scanned" it across a view, taking note note of the colour intensity reading at each "point", and then "mapped" those readings on paper with lil blobs of colour... what would you have?

    A photograph of the scene, that's what.

    There is no meaningful distinction between what you're asking for, and rendering.
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  12. #12
    Curmudgeon in Training Ma3rk's Avatar
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    I appreciate the feedback RH & I don't think I can get much more of a "knows what he's talkin' about" than that.

    Coming from the world of silver bromide & various chemical incantations, via stage & cinema lighting and all the way to the digital abilities of now, I was just hoping that one of you math wizards had some node formula that I could attach to a small sphere or half dome and tell me that sort of info. But, that's alright. Had to ask.
    "Never be a cat in a cartoon. Never." Chief Wiggum

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