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  1. #196
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    If you think of the blue light as having lost some wavelengths, and the magenta paint as removing more, then it's really a kind of subtractive mixing. Subtractive mixing is not as predictable as additive mixing, because it depends on the exact distribution of wavelengths reflected by the paint as well as in the light. But you could definitely say that the paint would appear more bluish, or even blue if the colour of the light was saturated (pure) enough. But you would also expect that the perceived colour of the paint would not change as much as the actual wavelengths change, because our visual system would partially discount the colour of the light (colour constancy).

    It's Doctor Briggs, by the way, but please call me David (or briggsy!).


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  3. #197
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    Oh Dr David , Your THAT DUDE , THE Color and Light dude....I have always had you in my favorites : ).... Brilliant Methodical writing dude ....Thankyou from a Oil painter who sees Color for all its worth ....... Thumping!!!!

  4. #198
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    thank you very much Doctor Briggs! ^^
    i think now i'm more understand now Doctor Briggs

    so when the color of light is losing wavelength or let say "not blue enough" then it subtractive with the surface isn't it?
    and if the light wavelength is 100% blue... then it's addictive with magenta?

    so the second row is subtractive... then the third row is addictive? (if i'm not wrong)

    sorry doctor... if my bad english is lost you somewhere... T^T

    (in fact i'm reading your answer about ten times and open google translate for the meaning, i've trying hardest to totally understand what u said, though my english is very bad but i'm severely dying enough to learn it from you Doctor ^^)

  5. #199
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    Not quite, it's all subtractive mixing. The blue lights have some of the red and green parts of the spectrum missing, and the magenta paint then absorbs some more wavelengths, so the process can be classed as subtractive mixing.

    The bottom row just shows squares copied out of the magenta row, against a grey background. These areas do not look as blue in the picture because of colour constancy.

    By the way, it's called additive mixing, not addictive mixing!

  6. #200
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    Awwww Briggsy, you were in Brisbane earlier this year only a few blocks from where I live? Damn, wish I'd known. I have only just discovered the Atelier in Salisbury and they've still got your April workshop advertised for some reason. But yes, that's looking rather scrumptious. Are you going to come back for another round any time soon? And how long will it be until HuevalueChroma is back up?


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  7. #201
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    Is the website down?

  8. #202
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    Thanks for alerting me guys - looks like the site was intermittently down for three days or so due to an issue with EveryDNS. All fixed now, thanks once again to help from Ben Green (scibotic).

    Sorry you missed the workshop Beeston! At least you've found the guys at Atelier - they're all awesome in different ways so make the most of them. Hopefully there'll be another two-day workshop in Brisbane at some stage; otherwise I run the full five-day workshop fairly regularly in Sydney, including one scheduled for the last week of this month if it gets a couple more students (anyone interested should let me know ASAP) and then again in January.

  9. #203
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    Constant saturation

    Hi, thank you so much for the awesome site. Its amazing such valuable information is free. So much better than any of the books out there.

    Just a question about the principle of uniform saturation. I noticed in a lot of photos where a white wall is lit by a light source that when you sample the colour of the wall in photoshop near the light it has a lower saturation than further away.

    The Dimensions of Colour - a colour theory discussion thread

    In the above the light source is on the left. The wall near the light has saturation of 18% and on the right the wall has saturation 27%. It's a bit hard to see in the image but the wall is white. Why has the saturation increased? Would this be because of ambient light? The light on the left is the only light source in the room. Wouldn't the ambient light be the same colour as the light source in this case? I assume the light is largely bouncing off other walls so wouldn't change much in hue.

    The saturation of the subject's skin also increases on the right (away from the light). Because the light colour is determined using subtractive blending doesn't this suggests that the ambient light is warmer than the direct light on the left? (Because a warmer ambient light has relatively more R than B and G it would tend to make the skin redder thus more saturated).

    Thanks very much for any help.

  10. #204
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    You're not giving me much to go on, fawnha(!), but we need to consider the objects in the room as well as the walls. If the objects are mostly blue, the ambient light would be bluer than the main light; if they are mostly brown, the ambient light would be more yellow/orange, which is what we seem to see.

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  12. #205
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    hi,

    what would you recommend me to get basics to advanced in color theory, the book "the New Munsell Student Color Set" or "Art of Color" by Johannes Itten?

    The munsell book is not as expesinve than Art of Color, but Art of Color is available in my mother tongue.. pld:

    i really would appreciate a bit of freedom in my head with alle the unanswered questions and vice versa..

    @briggsy, i admire your engagement! somehow, it seems to be too advanced for me, but wow..
    Last edited by Mister Janchichan; November 25th, 2011 at 12:00 PM.

  13. #206
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    I'll save briggsy the trouble of repeating himself:
    Quote Originally Posted by briggsy@ashtons View Post
    The real problem with Itten is not so much what is in the book as what isn't. Itten's conception of the scope of colour theory was strongly influenced by the Farbenlehre of Goethe (1810), which was a vitriolic and spectacularly misguided attack on the scientific approach to colour vision pioneered by Newton. Itten did at least admit that Newton was right about the spectrum, but otherwise, like Goethe, he ignored almost every development in our scientific understanding of colour after Newton. For example, like Goethe, he explained afterimages in terms of eye animism (the eye "requires" the complementary and "spontaneously generates" it if it isn't already present), not mentioning the fact that these phenomena had already been (at least partly) explained in terms of changing relative sensitivities of three receptors by Thomas Young in 1807 (and even earlier by Palmer).

    A bit like Betty Edwards is for drawing, Itten might arguably be ok as a very first introduction to colour if you know nothing about the subject, but you'll want to get beyond that level as soon as possible. His simplistic eighteenth century colour wheel is ok to communicate the basic idea of the circular dimension of hue, but you'll find that it doesn't actually work for mixing colours on your computer or with your paints, and you'll need different hue circles for each of these situations. The colour sphere he adopts (originally published by Goethe's friend Runge in 1810) is a good introduction to the basic conception of three dimensions of colour forming a space, but again you'll want to go beyond it to the more sophisticated conceptions of Munsell or Arthur Pope to put the conception into practice.

    It isn't really Itten's fault, but the continued widespread use of his book as the be all and end all of colour theory, nearly fifty years after it was written, and nearer a hundred after his ideas were formulated, is connected with a widespread and powerful tradition of ignorance in art teaching that refuses to engage with any scientific understanding of colour whatsoever. The scale of this great leap backwards is emphasized when you reflect that in the early twentieth century it was an art teacher, Albert Munsell, who invented the most widely used colour order system in the world.

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  14. #207
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    Quote Originally Posted by Elwell View Post
    I'll save briggsy the trouble of repeating himself:
    thanks, ill go with munsell!

  15. #208
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    Question Non-Linear Brightness and Luminance

    Dear Briggsy,

    As of now I still can't quiet understand one thing: The Conversion You did in Your two tables (for inclination angle and point source distance) from radiance to non-linear brightness.

    How did You convert them?

    But first let me see if I understood the meanings right now.

    Brightness is a human perceptual value and non-linear, compared to and being the "percieved equivalent" of Luminance, which stands for the physical value of radiance. Two different words are used, to clearify that we see slightly different from what we would expect to see from the physical values. A grey surface with 18% radiance for example, appears mid-tone grey to us, although logic would tell us it should be darker according to a value from 0% - 100%. So Brightness is non-linear in relation to Luminance and it's physical radiance values.

    Then You said Photoshop works with non-linear Brightness, in other words, the values from dark to light, dim to bright are graded according to human perception.

    Then I found one formula You mention on Your site for converting from non-linear Brightness to linear Brightness (non-linear Brightness = linear Brightness * 0.45).
    Does that mean linear Brightness = Luminance?
    If not, could You please clarify the difference between these three terms?
    And how to convert from Radiance to non-linear Brightness?

    I'm a little bit confused now about Lightness too. I thought Lightness was the one perceptual equivalent of Brightness in the beginning. Since it's comparing to a white surface. Now I notice You say they are both perceptual values.

    Luminance is the physical value of radiance, which can be physically, scientifically measured. (Okay, the others can to, but all basically in relation to this.)
    So, Brightness is the perceptual value of light going from dim to bright. The perceptual value of luminance.
    And Lightness is the perceptual value (the perception) of how bright any color seems to appear in relation to each other, including grey; generally compared to the "Lightness" of a white surface.
    Last edited by Shindoh; December 23rd, 2011 at 08:03 PM.

  16. #209
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    Hi Shindoh, I'd sum it up like this:

    Linear = scaled proportional to light energy
    Nonlinear = scaled proportional to human perception
    Radiance = light energy, scaled linearly
    Luminance = light energy, scaled linearly, but with the visual effectiveness of the spectral components factored in (i.e. green wavelengths count for more than blue, because they look brighter to us at the same amount of energy)
    Brightness = luminance, scaled nonlinearly
    Lightness = brightness of an object relative to the perceived brightness of a white object in the same setting.

    However Charles Poynton, whom I cite on the page where you got that formula, noted that so-called R, G and B "brightnesses" are sometimes given in linear units, and sometimes in nonlinear units, usually with no indication of which of the two is being used. "Linear brightness" of R,G or B would be the radiance (OR luminance) of each relative to their maximum radiance (OR luminance).

    Today RGB brightness values seem to be dominantly of the nonlinear kind, though I have encountered the linear kind occasionally. In the two tables I used the inverse square law and cosine relationship respectively to get the fall off of light energy, and then converted this to nonlinear brightness (like the B in HSB) using the *0.45 formula.

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  18. #210
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    Question

    Quote Originally Posted by briggsy@ashtons View Post
    Today RGB brightness values seem to be dominantly of the nonlinear kind, though I have encountered the linear kind occasionally. In the two tables I used the inverse square law and cosine relationship respectively to get the fall off of light energy, and then converted this to nonlinear brightness (like the B in HSB) using the *0.45 formula.
    This is where I feel like I am missing something.
    In Your table we have for example 25% Radiance becoming 54% Brightness. (?)
    However 25*0.45 = 11.25; and for the next one 11.11*0.45 = 4.9995.

    I can't understand how You got to those numbers.

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