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Thread: The Dimensions of Colour - a colour theory discussion thread

  1. #105
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    Thank you Mr Briggsy for the gem.

    I just had to see it on "the squre".
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  3. #106
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    Hi Briggsy and Zaorr,
    I haven't ditched the thread I just wanted to reply well. But there were some things that did not add up to me when I think about some of the information. And this just shows that no matter if you think you got it right, listen to what others have to say...cause I've been learning quite a bit here. What really made me think is why did you draw the area in full light just brighter and not lighter in value? I then realized that "maybe" it is backwards...that maybe loomis is considering diffused light and yours is specular light. The reason I say this is that "matte" objects are considered as having a diffused quality and the areas in full light, as the planes reach perpendicular to the light source, get lighter in value...Generally. When rendering matte objects...Form change = Value change. Well what gave me that "aha" moment is that I did a search of "red balls" on the internet and I noticed something. Almost all of the balls that I found, the "full light" areas to the "Half lit" areas were close to the same value...they looked pretty flat. And they were all specular...very shiny... and it makes sense that the half lit and full lit areas would be of similar value because the environment is being reflected to the viewer. Zaorr said this about my red ball and I agree that he is correct. So the values of the sky or room make up a somewhat "flat" plane and thus making the reflected half lit and full lit areas appear flat as well. Here are some photographic examples of what I am talking about. I also believe the the "lines" of the color picker for a "diffused" object would be curved towards the top and then head to white...given the earlier scenerio...Now that I look at the top "diffused" ball I think that the irregular shape of the half lit area is actually reflections of surrounding trees. I'll try the exercise on the earlier page and see what I come up with. Thanks guys!
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  4. #107
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    Jason. you're quite correct that the red colour does not change much in brightness within the full light area, but this is just what we expect of a diffuse reflection. If a plane facing the light source catches x amount of light energy, the same plane turned say 45 degrees from the light source will catch cosine 45 degrees or 0.7071 times x. You may also know that our perception of brightness is related in a nonlinear way to light energy, so that a surface that looks middle grey reflects only about 18% of the light reflected by a white surface. By the same relationship, our surface reflecting 0.7071 of the amount of light energy will look about seven-eighths as bright as a fully lit plane. So in turning halfway (45 degrees) from facing the light source, the perceived brightness of the light hitting and being reflected from the surface will drop by only one eighth. For a red or mid grey object this amounts to a change of only a little over half a point on the ten-point Munsell scale.

    So - form change creates value change, but only very slowly until we reach the half lights.

    On top of that, because our visual system pays less attention to gradual changes than abrupt changes, we tend not to notice even the small amount of change in lightness that does occur in the full light. (? which may be why you thought I had made the full light brighter but not lighter ??)

    I would describe what you've illustrated as the difference between a small/medium-sized light source and a very large light source, but it's true that the latter creates a saturation pattern like that described by Loomis in the full light and half light (although as you can see this tends to come with an indistinct terminator and shadow shape).
    Last edited by briggsy@ashtons; April 15th, 2009 at 09:49 PM.
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  6. #108
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    This thread has taught me not to look at specular as a surface condition but to look at the surface as it it's a mirror when dealing with specular regardless how dull it is.

    Those are nice balls Jason. Try looking at each as if they are mirrors and feel the light source and blue skies reflected in them. This will help you seperate surface diffuse from the blending reflection.

    I did another rendering study the other night and found myself placing the specular and some of the roof lit around the light source, I do believe now that this is the correct way to render speculars, for your mind to shift looking at form as if it's a mirror and then rendering the "source scene" as it may appear on the surface. No more turning a piece of the object into a bright spot mechanically like loomis would have.

    I baught some blue scrap books a while back and a nice white color pencil not knowing exactly what I should be doing with it. I guess now is a good time to take those out of the drawer.
    Last edited by George Abraham; April 16th, 2009 at 12:07 PM.
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  7. #109
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    Thank you for this valuable reference. How generous of you to make this available to us.
    Thank you!
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  8. #110
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    Briggsy (and others)- you might be interested in a Photoshop script I wrote that generates a digital approximation of HVC strings in the swatch palette:

    http://www.conceptart.org/forums/sho...1&postcount=11
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  10. #111
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    Great work Tim! It actually generates hue-value-saturation strings, but they are at least as useful as HVC strings, in their own way, for physical paint as well as digital.

    Quite apart from its practical use, the swatches should have a great educational use in helping people to learn to think in terms of an absolute tonal scale of Munsell values.

    I look forward to giving it a try!
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  11. #112
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    I'm glad you like them David! I'd love to hear any feedback you might have on the script.

    I'm contemplating a version which would let you specify saturations on a per-hue basis (rather than applying the same saturations to every hue). It would require the user to learn a special syntax to enter the desired values, but it could be a little more useful & flexible for those willing to brave it (I'd probably choose something close to the HVC slash notation). I'm also contemplating a really fancy version that would only work in CS4, but would allow you to "mix" between swatches on the fly- so that if you wanted to knock the saturation of the current color down a bit you could click on the corresponding gray a couple times, which influence the current color but not replace it. This would be pretty complicated, but a great simulation of painting with strings in oil. But that won't happen for a while- I've been tinkering with the tools too much lately and not painting enough with them!
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  12. #113
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    Excellent info!!
    But where did the site go?! www.huevaluechroma.com - it worked a few days ago, will it come back?
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  13. #114
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    It looks like it's been down for most of the weekend our time. I've just sent off an email to ibiblio, so hopefully I'll know something soon. Glad to know it's missed!
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  14. #115
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    OK, it was just a small glitch at ibiblio, which they fixed straight away. If you're still getting the redirect page, just empty your cache.
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  16. #116
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    Mr. Briggs sirrrrrr, I have opened pandora's box again and have become rather confused. I've been going over some of the old Peer Project exercises recently for CA's mentoring and got stumped by one of my own questions! Well, it's not that I don't know the answer I wanted at the time; it's that I think I was wrong!

    It's an hypothetical exercise with an object of a pure hue in an environment with a single pure and direct lightsource.


    The question is as follows; The lightsource is pure red and pure yellow. Our object is green. What do you see?

    In my old train of thought I would have said you would see as the end result a yellow sphere. But now I can't help but shake the feeling that you would see a green sphere though perhaps a bit dark...

    Can you help untwist my brain as you always have?

    The exercise for reference if necessary.
    http://www.conceptart.org/forums/sho...45&postcount=5
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  17. #117
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    Hi Tom

    I think the crucial question is what we mean by a green object "of a pure hue". Probably not an object that reflected only monochromatic green light - such an object would appear very dark or black under any other light source. There is a theoretical concept of "optimal" colours that reflect all wavelengths in a given band of wavelengths, and none outside that band. Optimal green surfaces range in theory from darker more saturated greens (reflecting a relatively narrow band of wavelengths) to brighter but less saturated greens (reflecting a broader band). So the answer really depends on which of these it is - the former would reflect neither red nor yellow monochromatic light, but the latter might well reflect yellow. How does that sound?
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