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The words "predict" and "prediction" are used here and in the original article on Oklab in a way that I'm not familiar with. For example: > For this reason I

The words "predict" and "prediction" are used here and in the original article on Oklab in a way that I'm not familiar with. For example: > For this reason I have designed a new perceptual color space, designed to be simple to use, while doing a good job at predicting perceived lightness, chroma and hue. What does it mean for a color space to predict lightness, chroma, and hue?

chrismorgan 6y ago
It’s the normal sense of the words, because it’s about perception rather than any hard ground truth. Hence “predicting perceived lightness, chroma and hue”. We don’t know how any given person will see and interpret light, so it’s all about guessing what will look right to most people.
- rodarmor 6y ago
  It's a bit strange to me, because how does a colorspace "predict" anything? But maybe I get it. Is it that since a lab colorspace has lightness and opponent color coordinates, a lab colorspace, for example, "predicts lightness well" when a small increase in the L coordinate leads to a small increase in the perceived lightness of the resultant color?
  - chrismorgan 6y ago
    The gradients offer good examples. Take the blue–white gradient: that’s about saying “what happens if we take a certain blue, and lighten it?” Expressed otherwise: “given ‘blue’, what do people think ‘light blue’ is?” It’s predicting light blue, based on the shape baked into the colour model. sRGB blending says “blue channel’s already full, let’s increase the red and green channels”. That’s tolerable, but not great. Most people will look at it and be very subtly discontent, though they probably can’t quite place their finger on what’s wrong with it. It’s just a little too indigo. CIELAB does a terrible job of this particular prediction. People will tend to agree that its guess at light blue is actually a light purple. IPT, Oklab and ICtCp have been modelled to know that, in order to lighten a blue, you actually have to add a little more green than red (increase the green channel more than the red channel), because that’s just how our eyes and brains work, how we perceive colours. Or the blue–yellow gradient: it’s asking “what colour is half-way between blue and yellow?” sRGB thinks a mid-grey is, and CIELAB thinks mauve is: these two are quite clearly wrong. The interesting ones are that IPT and ICtCp think a sort of teal is, while Oklab thinks it’s a bit paler and not quite so green. These are the predictions that have been designed into the colour space. Who’s more correct? I dunno, actually. They’re both pleasant to look at.
    - rodarmor 6y ago
      This is a great explanation! Thank you, it makes perfect sense now.
  - deleted 6y ago
    [deleted]
raphlinus 6y ago
It's a good point, I wasn't precise in my language. A good way to understand it is that if two different colors have the same lightness (or hue, or saturation) in some color space, that "predicts" that they will be perceived to have the same lightness as well. It's impossible to get these predictions exactly right (in part because actual perception depends on so many variables), but some can be better than others. Another useful function of a color space is to predict the threshold of when two similar colors are just barely perceptibly different.
- kelsolaar 6y ago
  > Another useful function of a “perceptually uniform” colorspace. Not all the colourspaces are perceptually uniform nor try to be. For example, CIE XYZ is photometrically linear and appropriately so!
  - jacobolus 6y ago
    XYZ does not provide correlates of hue, lightness, brightness, chroma, colorfulness, saturation, blueness–yellowness, redness–greenness, or the like Y = relative luminance, XYZ are tristimulus coordinates, and x, y or u', v' are chromaticity coordinates. These are all physical rather than perceptual quantities.
  - roel_v 6y ago
    I'm a bit lost in the discussion here - is your first line a correction of the GP and you used the > mark 'wrong', or did the GP update his post and is the quote not in there any more?
    - raphlinus 6y ago
      The first. I should have added "perceptually uniform," kelsolaar is correct.
- rodarmor 6y ago
  That makes sense, thank you!

chrismorgan 6y ago

It’s the normal sense of the words, because it’s about perception rather than any hard ground truth. Hence “predicting perceived lightness, chroma and hue”. We don’t know how any given person will see and interpret light, so it’s all about guessing what will look right to most people.

rodarmor 6y ago
It's a bit strange to me, because how does a colorspace "predict" anything? But maybe I get it. Is it that since a lab colorspace has lightness and opponent color coordinates, a lab colorspace, for example, "predicts lightness well" when a small increase in the L coordinate leads to a small increase in the perceived lightness of the resultant color?
- chrismorgan 6y ago
  The gradients offer good examples. Take the blue–white gradient: that’s about saying “what happens if we take a certain blue, and lighten it?” Expressed otherwise: “given ‘blue’, what do people think ‘light blue’ is?” It’s predicting light blue, based on the shape baked into the colour model. sRGB blending says “blue channel’s already full, let’s increase the red and green channels”. That’s tolerable, but not great. Most people will look at it and be very subtly discontent, though they probably can’t quite place their finger on what’s wrong with it. It’s just a little too indigo. CIELAB does a terrible job of this particular prediction. People will tend to agree that its guess at light blue is actually a light purple. IPT, Oklab and ICtCp have been modelled to know that, in order to lighten a blue, you actually have to add a little more green than red (increase the green channel more than the red channel), because that’s just how our eyes and brains work, how we perceive colours. Or the blue–yellow gradient: it’s asking “what colour is half-way between blue and yellow?” sRGB thinks a mid-grey is, and CIELAB thinks mauve is: these two are quite clearly wrong. The interesting ones are that IPT and ICtCp think a sort of teal is, while Oklab thinks it’s a bit paler and not quite so green. These are the predictions that have been designed into the colour space. Who’s more correct? I dunno, actually. They’re both pleasant to look at.
  - rodarmor 6y ago
    This is a great explanation! Thank you, it makes perfect sense now.
- deleted 6y ago
  [deleted]

raphlinus 6y ago

It's a good point, I wasn't precise in my language. A good way to understand it is that if two different colors have the same lightness (or hue, or saturation) in some color space, that "predicts" that they will be perceived to have the same lightness as well. It's impossible to get these predictions exactly right (in part because actual perception depends on so many variables), but some can be better than others. Another useful function of a color space is to predict the threshold of when two similar colors are just barely perceptibly different.

kelsolaar 6y ago
> Another useful function of a “perceptually uniform” colorspace. Not all the colourspaces are perceptually uniform nor try to be. For example, CIE XYZ is photometrically linear and appropriately so!
- jacobolus 6y ago
  XYZ does not provide correlates of hue, lightness, brightness, chroma, colorfulness, saturation, blueness–yellowness, redness–greenness, or the like Y = relative luminance, XYZ are tristimulus coordinates, and x, y or u', v' are chromaticity coordinates. These are all physical rather than perceptual quantities.
- roel_v 6y ago
  I'm a bit lost in the discussion here - is your first line a correction of the GP and you used the > mark 'wrong', or did the GP update his post and is the quote not in there any more?
  - raphlinus 6y ago
    The first. I should have added "perceptually uniform," kelsolaar is correct.
rodarmor 6y ago
That makes sense, thank you!