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> You probably didn’t set your light or color intensities in three.js using physical units in the first place, Nod... unless you're using a color space, like J

> You probably didn’t set your light or color intensities in three.js using physical units in the first place, Nod... unless you're using a color space, like Jzazbz, with an absolute (not relative) transfer function. Application context then motivates the nit pick. So a Jzazbz HDR of [0..10k], might get a daylight 1k nits picked for diffuse (non-highlight) white. Thus I appreciate it when color libraries provide a distinct Absolute XYZ D65 data type.

dahart 4y ago
This is a good point! Jzazbz is a good example of the (somewhat rare) application of perceptual response functions in high dynamic range. I’d be curious to hear what reasons you have to use Jzazbz. The color space seems best at scenarios where you need to compute HDR color differences. Most people don’t need that, but some advanced users like you do. Worth noting in this context that Jzazbz is non-linear, and even though it’s HDR, it still requires conversion to a linear space in order to blend colors physically. I want to elaborate just slightly on what I meant. In CG, like in real photography, the photographer almost always sets some combination of their exposure, aperture size, and/or white balance values manually, regardless of how well they’re controlling inputs and color spaces. As a simple example, I can always dim the lights by a factor of 2 power, and also either expose for twice as long, or open my shutter by one f-stop. When I dim lights by half and expose by double, then nothing about the image changes. Even if you know the physical luminosity of your lights, the overall process (usually) still cancels scale factors and at the end reduces to an arbitrary scaling that essentially sets the output white and output black to the brightest and darkest colors I want to show, respectively. With real film, there are additional arbitrary scaling values like the film development process, and lighting conditions when viewing. With digital, the display’s scaling is frequently unknown, and thus arbitrary; you might use 1k nits for your daylight diffuse, but that’s not what your monitor actually shows you. There are legit use-cases for wanting absolute physical values in the intermediate stages, and using a “linear” color space for blending is, in a way, emulating exactly that desire but still with an arbitrary scale because the input brightness and/or output brightness are being tuned by hand.
- mncharity 4y ago
  > I’d be curious to hear what reasons you have to use Jzazbz I needed a color space for teaching, so I'm using it to kludge wide-gamut hue linearity onto CAM16UCS. I wish I knew of something better to do. Backstory is, I've long struggled to find community of interested and discussion, around the idea of transformatively improving science education content by collaboratively applying vastly greater-than-usual domain expertise. I thought to troll with a worked example, and chose "color". Even though "I'm building hard thing solo, because I really don't want to build such things solo?!?"... sigh. Color is pervasively taught in early primary, but with such poor content and outcomes, that foundational confusion persists even among first-tier physical-sciences graduate students. So: might color be taught more clearly by emphasizing spectra, in early primary? With web interactives? It seemed a question to explore. So I needed a perceptual color space optimized for learning color. A rather different objective than usually drives color space design. Computability doesn't matter, as small lookup tables suffice. But noticeable features from eyeballing the space should be "yes, that's color perception", not "oh, no, that's an artifact of the model - try to ignore that aspect". The usual art/science education "one part careful, nine+ parts misleading bogosity" just doesn't end well. CAM16UCS is generally good at avoiding "that... doesn't look plausible". Better than other UCSs I skimmed. But... hue gets curvy near its edges, especially badly in blue. Jzazbz regrettably fails the "space looks plausible" test, but is wide-gamut, and has nice hue linearity. So I'm using it to kludge greater linearity onto CAM16UCS, between sRGB gamut and visible boundary. Which aids understandably coupling space to spectra. Getting from daylight to banana to spectra and apparent spectra and color space, provides a lot of opportunity to get things wrong. And from interactive draw-a-spectra. Swapping in Jzazbz for end-to-end HDR physical units provides the warm fuzzy of sanity check. Thus three.js intensities in nits, and an opportunity for Sunday punning. It's just a silly niche use case, rather than advanced use, but modulo burn out, I'll be back at it tomorrow. Also... there's an order-of-magnitude luminance "why don't you see a sky full of stars" interactive somewhere on my infinite todo list, so getting perceptual luminace right had additional motivation. Though that will have to handle meso and scotopic perception... sigh. Appreciated your comments.
  - dahart 4y ago
    Hey that’s really cool and not silly or niche at all, I actually think it’s extra advanced to not just understand color so deeply but try to teach it at that level. Pretty hard core in my book, color is a surprisingly hard and deep subject. I had a few good teachers along the way who taught me a ton about color and computer graphics. Peter Shirley is probably the top of my personal list, and he’s also very interested in improving science education, so maybe worth checking out his CG books. In his rendering class we bought a MacBeth color checker and had to take a photograph of it set inside a scene that we physically built out of whatever materials and light sources we wanted, and then we had to write our own renderers to match the photo. You really learn a lot about color trying to do that! :) Pete and I have since designed a simple opponent-process color space aimed at ease of use that is perceptually uniform ‘enough’, but we haven’t published it yet. That could be a fun way to teach though: have students design their own color space! There also might be some interesting work going on in the area of digital color picker interfaces that could be useful for teaching. I’m forgetting who does this stuff, so can’t cough up any links at the moment, but I’ve definitely seen a couple of neat presentations recently that combine the science of perception and color spaces along with good design sensibilities to make interfaces that are demonstrably better for artists than the crappy RGB & HSV & other pickers we usually see today.

dahart 4y ago

This is a good point! Jzazbz is a good example of the (somewhat rare) application of perceptual response functions in high dynamic range. I’d be curious to hear what reasons you have to use Jzazbz. The color space seems best at scenarios where you need to compute HDR color differences. Most people don’t need that, but some advanced users like you do. Worth noting in this context that Jzazbz is non-linear, and even though it’s HDR, it still requires conversion to a linear space in order to blend colors physically. I want to elaborate just slightly on what I meant. In CG, like in real photography, the photographer almost always sets some combination of their exposure, aperture size, and/or white balance values manually, regardless of how well they’re controlling inputs and color spaces. As a simple example, I can always dim the lights by a factor of 2 power, and also either expose for twice as long, or open my shutter by one f-stop. When I dim lights by half and expose by double, then nothing about the image changes. Even if you know the physical luminosity of your lights, the overall process (usually) still cancels scale factors and at the end reduces to an arbitrary scaling that essentially sets the output white and output black to the brightest and darkest colors I want to show, respectively. With real film, there are additional arbitrary scaling values like the film development process, and lighting conditions when viewing. With digital, the display’s scaling is frequently unknown, and thus arbitrary; you might use 1k nits for your daylight diffuse, but that’s not what your monitor actually shows you. There are legit use-cases for wanting absolute physical values in the intermediate stages, and using a “linear” color space for blending is, in a way, emulating exactly that desire but still with an arbitrary scale because the input brightness and/or output brightness are being tuned by hand.

mncharity 4y ago
> I’d be curious to hear what reasons you have to use Jzazbz I needed a color space for teaching, so I'm using it to kludge wide-gamut hue linearity onto CAM16UCS. I wish I knew of something better to do. Backstory is, I've long struggled to find community of interested and discussion, around the idea of transformatively improving science education content by collaboratively applying vastly greater-than-usual domain expertise. I thought to troll with a worked example, and chose "color". Even though "I'm building hard thing solo, because I really don't want to build such things solo?!?"... sigh. Color is pervasively taught in early primary, but with such poor content and outcomes, that foundational confusion persists even among first-tier physical-sciences graduate students. So: might color be taught more clearly by emphasizing spectra, in early primary? With web interactives? It seemed a question to explore. So I needed a perceptual color space optimized for learning color. A rather different objective than usually drives color space design. Computability doesn't matter, as small lookup tables suffice. But noticeable features from eyeballing the space should be "yes, that's color perception", not "oh, no, that's an artifact of the model - try to ignore that aspect". The usual art/science education "one part careful, nine+ parts misleading bogosity" just doesn't end well. CAM16UCS is generally good at avoiding "that... doesn't look plausible". Better than other UCSs I skimmed. But... hue gets curvy near its edges, especially badly in blue. Jzazbz regrettably fails the "space looks plausible" test, but is wide-gamut, and has nice hue linearity. So I'm using it to kludge greater linearity onto CAM16UCS, between sRGB gamut and visible boundary. Which aids understandably coupling space to spectra. Getting from daylight to banana to spectra and apparent spectra and color space, provides a lot of opportunity to get things wrong. And from interactive draw-a-spectra. Swapping in Jzazbz for end-to-end HDR physical units provides the warm fuzzy of sanity check. Thus three.js intensities in nits, and an opportunity for Sunday punning. It's just a silly niche use case, rather than advanced use, but modulo burn out, I'll be back at it tomorrow. Also... there's an order-of-magnitude luminance "why don't you see a sky full of stars" interactive somewhere on my infinite todo list, so getting perceptual luminace right had additional motivation. Though that will have to handle meso and scotopic perception... sigh. Appreciated your comments.
- dahart 4y ago
  Hey that’s really cool and not silly or niche at all, I actually think it’s extra advanced to not just understand color so deeply but try to teach it at that level. Pretty hard core in my book, color is a surprisingly hard and deep subject. I had a few good teachers along the way who taught me a ton about color and computer graphics. Peter Shirley is probably the top of my personal list, and he’s also very interested in improving science education, so maybe worth checking out his CG books. In his rendering class we bought a MacBeth color checker and had to take a photograph of it set inside a scene that we physically built out of whatever materials and light sources we wanted, and then we had to write our own renderers to match the photo. You really learn a lot about color trying to do that! :) Pete and I have since designed a simple opponent-process color space aimed at ease of use that is perceptually uniform ‘enough’, but we haven’t published it yet. That could be a fun way to teach though: have students design their own color space! There also might be some interesting work going on in the area of digital color picker interfaces that could be useful for teaching. I’m forgetting who does this stuff, so can’t cough up any links at the moment, but I’ve definitely seen a couple of neat presentations recently that combine the science of perception and color spaces along with good design sensibilities to make interfaces that are demonstrably better for artists than the crappy RGB & HSV & other pickers we usually see today.