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

  1. #170
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    You're welcome, draw and spinor!

    Thanks for taking the trouble, Bob. They're all very good questions.

    Birren's "uniform chroma scales"


    Quote Originally Posted by bbshrmn View Post
    in faber birren's book 'creative color' he mentions, "the most beautiful of all formal color gradations that is known" as the "uniform chroma scale-which have the same apparent color content but which differ in lightness and darkness." is that in fact, the same thing as your described "uniform saturation shading series?" (if its not, how are they related as to what happens in nature?)
    What Birren calls "uniform chroma scales" are the perceptual (or logarithmic) "isochromes" of the Ostwald system, which is not really used any more. Ostwald's perceptual isochromes were in theory lines of uniform saturation in my terminology, though in practice (in the Ostwald colour atlas) they seem to me to be somewhere between lines of uniform saturation and lines of uniform chroma.


    Mixing a shading series

    Quote Originally Posted by bbshrmn View Post
    1. doesn't much care still need to be taken with the tint, tone and shade to ensure they are constant in color saturation amongst themselves? this doesnt just happen naturally, right?
    2. assuming you have step 1(question 1) done correct, is he implying that all in-between steps will then be balanced, saturation wise, inherently? if so, by that logic, couldnt i do away with mixing the tone all together and just use the tint and the shade to make the tone? and if not then it would seem this whole approach falls apart a bit.
    3. lastly, if i use red, add black and then a bit more red again to bring it back on the saturation line, couldnt i have just used less black to begin with or is it not the same thing? how does this affect step one?
    1. Of course, and of course.
    2. Mixtures between successive steps tend to drift off the uniform saturation line, so the steps should be kept close together.
    3. if you are shading red+black+white by adding black, you correct the saturation with red (not red+black+white). If you are shading a pure opaque red with black, there is less of a tendency for the saturation to drop, but if it does you could boost the saturation with a transparent red. Adding some of the opaque red would of course just take you back in the direction you came from).


    Uniform-saturation series and illumination

    Quote Originally Posted by bbshrmn View Post
    ok, sorry, i guess there is one other thing as well. so what is the proof/evidence that this is actually true and that saturation doesnt decrease or increase in the shadows? im guessing the shoddy results of just color sampling images isnt enough.
    I'll answer that by showing you some uniform saturation series and asking what you see. The main rectangle of the attached jpg simply shows seven uniform saturation series (one achromatic). We automatically see it as an image of uniform object colours under varying illumination. To me this simple demonstration neatly proves that
    (1) our visual system recognizes relationships of uniform saturation in the visual field, and
    (2) it uses these relationships in its amazing capacity to separate effects of illumination from effects of object colour (object-colour constancy).
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  3. #171
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    uniform saturation series

    Quote Originally Posted by briggsy@ashtons View Post
    I'll answer that by showing you some uniform saturation series and asking what you see. The main rectangle of the attached jpg simply shows seven uniform saturation series (one achromatic). We automatically see it as an image of uniform object colours under varying illumination. To me this simple demonstration neatly proves that
    (1) our visual system recognizes relationships of uniform saturation in the visual field, and
    (2) it uses these relationships in its amazing capacity to separate effects of illumination from effects of object colour (object-colour constancy).
    thanks for the quick reply.

    ... but does this example, starting out with some colors that arent so crisp and saturated to begin with, not work just as well? this reads very natural and as uniform object colors also, no?
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    Quote Originally Posted by briggsy@ashtons View Post
    What Birren calls "uniform chroma scales" are the perceptual (or logarithmic) "isochromes" of the Ostwald system, which is not really used any more.
    And thank goodness for that! Creative Color is overall a good book, but Birren's big flaw was his attachment to Ostwald.

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  5. #173
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    Quote Originally Posted by bbshrmn View Post
    ... but does this example, starting out with some colors that arent so crisp and saturated to begin with, not work just as well? this reads very natural and as uniform object colors also, no?
    Not as natural as when you shade the same colours keeping the saturation uniform:
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    Quote Originally Posted by briggsy@ashtons View Post
    Not as natural as when you shade the same colours keeping the saturation uniform:
    yeah, it appears so. given that its the same illumination range, your colors definitely appear to be passing into the darkness, where mine feel to be coming out of it a bit. thank you thats helpful.

    i was also trying to color sample some HDR images to see what kind of results i would get since they are supposed to be closer to how we perceive reality and i did find mostly uniform saturation throughout them. that said, the saturation was often at 100%. if you will accept the loose terms, why the 'blow out' and are these HDR images better for us to study, from a 'reality standpoint'? are they just constantly pushing the outer limits of the technologies involved, how does this relate to paint?

    thank you.
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  7. #175
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    Sorry, Bob, I'm a bit vague on the details of HDR image processing at the moment, so I'll have to pass on those four(!) new questions for now. A digital camera is in a way a kind of inexpensive spectrophotometer, and you can very usefully investigate some things using digital photos, but I'd be much more inclined to use a straightforward image, aware of its limitations, than one that is higly manipulated in a way I don't fully understand.
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    ok, thank you and sorry for the bombardment. so much to know and so little time.
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    I decided to go back to the basics and learn as much as I can about value, saturation and hue, and I would just like to say that, as much as how your site gave me a headache trying to understand it on my own, thanks so much for such an invaluable resource Briggsy.

    As of the moment, I'm alternating between Gnomon Workshop's Light and Color and your website for studying, and already, my brain is trying to understand the difference between chroma and saturation, and I feel my brain bleeding. I'll continue my reading and studying and hopefully, once I get familiar with the technical aspects of the subject, everything will be that much clearer for me.

    Thanks!
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  10. #178
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    Saturation

    Everything about colour is more complicated than many people assume, so a little bit of bleeding is probably a good sign! Saturation especially is a word that requires caution, because it has several different meanings, which people using the word are often not conscious of.

    Some people use the word "saturation" for the purity of colours of surfaces, with these colours being considered as mixtures of white, "pure colour", and black, and saturation as the proportion of the "pure colour" component in the mix. People who say that chroma is "very similar" to saturation may simply be confused, but they may also be using saturation in this sense, which in effect means relative chroma - i.e. chroma as a percentage of the chroma of the "pure colour". This concept of "pure colour" is very problematic in relation to surfaces, however, so the open ended scale of chroma is much better.

    In Photoshop, saturation is the colour purity of the light that is emitted from the screen. Any light can be considered to be a mixture of a certain percentage of white light, plus coloured light: saturation in this sense is simply one minus the proportion of white light. I use saturation in this second sense, as explained on this page:
    http://www.huevaluechroma.com/093.php

    Colours like B and C in Figure 9.8 on that page have low chroma, and low saturation in the first sense, because as surface colours they contain a lot of black, but they have high saturation in the second sense, because the light given off is pure red (only the red phosphors are glowing).

    Not sure if that will help or not, but anyway a close study of the figure I just mentioned usually seems to get the idea across.
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  12. #179
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    light and shadow

    I'd like to pose a technical question. I am quite familiar with the color theory in general (we had that class back at Academy), and rules and guidelines in particular, yet there are some instances in which I am not 100% certain about the correct procedure.

    For instance, one of those guidelines is that the lightest dark is darker than the darkest light. (It is not always valid. I mean - it only applies to certain kinds of light under certain conditions. In overcast light, such rules do not apply. Even in sunlight, a very light ground surface can significantly raise shadow values.)

    What I'd like to know is how one shoud draw an area in light which local hue is equally dark or darker than the shadow? Take an apple for instance (or people with really ruddy cheeks). Apple may be yellow/green in hue, appearing rather high value in light, but there is large dark red spot which is partially in light and partially in shadow. That intense, dark red is of equal value as adjacent shadow. If one draws it as he sees it, the drawing may look somewhat odd; the apple will appear flat with oddly looking shadow. I mean - form shadow will go nicely around the form, creating the illusion of roundness, but the shape of adjacent red spot of equal value will confuse the viewer. What one should do in that case?

    Should one neglect what he sees in order to create a convincing illusion of form? Should he draw the mentioned dark spot (or say, ruddy cheeks) lighter than it appears, in order to prevent merging it with the shape of the shadow ?
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  13. #180
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    "Always keep the lightest dark darker than the darkest light".

    I'm really glad you brought this up Valentino, because this particular piece of advice is doled out far too often on these forums. It's not just that it's wrong factually, it's also very bad teaching to hand out simplistic "rules" instead of encouraging analysis and understanding.

    You're perfectly correct that the rule only applies under certain conditions. The brightness of any point is the brightness of the illumination multiplied by the reflectance of the surface. It should be clear from this diagram that the rule can not possibly hold if there are dark and light local colours involved, unless the contrast between the illumination in the light and in the shadow is very high. If the rule has any validity it is as a statement of aesthetic preference, not physical fact.

    The Dimensions of Colour - a colour theory discussion thread

    It would be better to say "Always make your lighting so contrasty that the lightest shadow is darker than the darkest light". At least that would make the limitations of the "rule" more obvious.

    I don't agree that painting your subject as it appears, ignoring the rule, will make it "appear flat" or create an "oddly looking shadow". All it will do is cause the pattern of lights and darks in your picture to differ a little from the pattern of light and shadow. That's it!
    Last edited by briggsy@ashtons; June 2nd, 2011 at 09:10 PM.
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  15. #181
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    Thanks for the reply. I'd be grateful if you or someone else could address the second question I posed:
    What should one do if he/she has to draw or paint the area (say - ruddy cheeks or dark spots on an apple) that has equal local value (in light) as adjacent shadow. Should one keep its value (in light) equal as the value of shadow?
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  16. #182
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    Sorry if I wasn't clear, my answer was: ignore the rule and paint it as it is - it shouldn't confuse anyone.
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