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

  1. #261
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    Overall the applets and explanations on that site are very good, but just on that last page you linked to there are a couple of things that could be confusing to students. I don't think it is stressed enough that all actual yellow, cyan amd magenta pigments are of the second, "broad C,M,Y" type, and I doubt that the narrower, essentially theoretical CMY colours in the first applet would be as bright as they are shown. (In fact the displayed colours are definitely not accurate, because when I add light from the red and orange parts of the spectrum to the narrow "yellow" spectrum, the displayed colour gets darker). Also in the summing up at the end, while it is correct to say that the additive/subtractive primaries "don't need to be" R,G,B/C,M,Y respectively, it is potentially misleading not to emphasize that those primaries do give the maximum gamut.
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  3. #262
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    I'd like some help to see if a diagram I'm working on is looking right for most observers/monitors.

    Please click on the link and observe each of the two finely-lined squares at the bottom of the diagram from a distance of a couple of metres or so, so that the vertical lines are no longer visible. Please check that your browser is set to 100% zoom, and very importantly, position yourself so that your line of sight to the square you are looking at is at exactly 90 degrees to the screen. If your browser resizes the diagram, please click on it to return it to full size. Do the squares look grey or coloured?

    http://www.huevaluechroma.com/pics/4.3.3.jpg
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  5. #263
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    Quote Originally Posted by briggsy@ashtons View Post
    I Do the squares look grey or coloured?

    http://www.huevaluechroma.com/pics/4.3.3.jpg
    Square (A) looks colored (light purple) Square (B) looks grey to me.
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  7. #264
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    Thanks first and foremost for your website, it was extremely informative and has helped me no end in my artistic growth. I am very much grateful.

    I have this idea, I want to desaturate the pure (100% saturation) colours in order to find out their values in black and white as a reminder.

    Would this be possible using the desaturate or greyscale function in ps? Would it be inaccurate or misleading?
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  8. #265
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    You're very welcome, and thanks for asking your questions here, Care.

    The answer to your first question is that you can either use the desaturate command in Lab mode (not RGB mode), or convert to greyscale mode, among other methods that achieve the exact same result, i.e. conversion of each colour to a grey of the same "L".

    My answer to your second question is that it seems this conversion may sometimes be somewhat inaccurate or misleading for some colours (mainly high saturation blues), but there may not be any better general solution. Here's why:

    In the attachment each coloured square is on a background of a grey of the same value according to these methods.

    The red square may look at first glance to be lighter than the grey background, but if I squint I can see that it is actually similar, or at least much more similar in value than it first seems. So I think that this is probably just an example of the impression of extra lightness that strong colours seem to possess, which been called "chromatic luminance" or the Helmholtz–Kohlrausch effect.

    However, no matter how much I squint, the blue square still looks lighter to me than the grey surround, so I'd have to say that it actually is lighter. A possible explanation is that the blue "phosphor" of my laptop is less violet/less saturated than that assumed for the conversion, which would make pure blue (B255) relatively bright on my screen, and also pure yellow (white minus blue) a little less bright. So maybe there's no conversion that will be perfectly accurate for all monitors.

    If anyone has any ideas please comment!

    A separate issue is that on most laptops the relative values of the colours and the greys change alarmingly with viewing angle; my observations were made looking flat on to the screen.
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    Last edited by briggsy@ashtons; December 6th, 2012 at 06:52 PM.
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  9. #266
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    thanks briggs you always come through, i really enjoy how u manage to verbalize things that i suppose we must unconsciously recognize, everytime you explain something i get that aaaa now it makes sense moment...

    like i feared, there might not be an all encompassing way to accurately determine this. but its no big deal. i guess its just a case of learning the exceptions to the rule etc
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  10. #267
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    This year my regular classes are (so far) all on late afternoons, evenings and weekends, which means I'll be available to run a few 5-day colour workshops more or less on demand at my studio in Sydney. The focus can be either on theory, or on putting the theory into practice using traditional or digital media. If anyone is interested please email me to discuss suitable dates.

    Here's a still life demo from the first one last week.
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  11. #268
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    Quote Originally Posted by briggsy@ashtons View Post
    In the attachment each coloured square is on a background of a grey of the same value according to these methods.

    The red square may look at first glance to be lighter than the grey background, but if I squint I can see that it is actually similar, or at least much more similar in value than it first seems. So I think that this is probably just an example of the impression of extra lightness that strong colours seem to possess, which been called "chromatic luminance" or the Helmholtz–Kohlrausch effect.

    However, no matter how much I squint, the blue square still looks lighter to me than the grey surround, so I'd have to say that it actually is lighter. A possible explanation is that the blue "phosphor" of my laptop is less violet/less saturated than that assumed for the conversion, which would make pure blue (B255) relatively bright on my screen, and also pure yellow (white minus blue) a little less bright. So maybe there's no conversion that will be perfectly accurate for all monitors.
    The value of that blue looks pretty good to me when I squint (at least equivalent to the red in terms of matching the ground), so I'd say your suspicion about the phosphors is probably right.

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  13. #269
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    Not sure if this is appropriate place to say it, but I appreciate the feedback on my SB and all the help you've given this community towards questions on color and light, sir.
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    Quote Originally Posted by Elwell View Post
    The value of that blue looks pretty good to me when I squint (at least equivalent to the red in terms of matching the ground), so I'd say your suspicion about the phosphors is probably right.
    Just a followup to that, I'm checking this thread today from a school computer, and the blue looks fine, but the red is appreciably darker than its corresponding gray.

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  16. #271
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    Quote Originally Posted by MrFrenik View Post
    Not sure if this is appropriate place to say it, but I appreciate the feedback on my SB and all the help you've given this community towards questions on color and light, sir.
    Thanks very much for the comment and for dropping by here!

    I'll repost a demo and some comments here that I just posted on MrFrenik's sketchbook in case anyone is interested. His aim was to paint a ball under a light source such that "the ball was a rather saturated green and matte surfaced, the light source is supposed to be the sun (almost noon) and the table is supposed to be the ground".

    My comments on the demo below: "The basic process is really quite simple: Work out the pattern of light created by each light source (including refllectors) separately, and then superimpose and combine these patterns additively using linear dodge mode. (The shadows will take care of themselves). Apply local colour using a layer in multiply mode.

    A couple of points arising from this example: Blue skylight tends to neutralize the yellowish cast of the sunlight around noon, so I wouldn't expect the up planes to be particularly yellowish/orangeish (unless the atmosphere was very smoky). Also, notice that a strong local colour tends to mask the variations in the colour of the lighting."
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  17. #272
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    Quote Originally Posted by Elwell View Post
    Just a followup to that, I'm checking this thread today from a school computer, and the blue looks fine, but the red is appreciably darker than its corresponding gray.
    Thanks again Tristan. Makes you wonder what people actually see on their screens.
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  18. #273
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    ive cleaned up my last post as it was full of my confusion i had before i finished stuying to the hole thread in about 8 hours maybe its because my brain died but i will have a little sleeping-break. it think it takes some time to get into practive, hopefully i am allowed to ask upcomming questions in the future.. i will leave my last question about the posted picture as it still isnt clear for myself..

    how would you describe the desaturation on the pink cloth in the highlight? is it cause it is reflective? i still find it hard to get this right in my imagination... the loomis approach was easier to follow, but i want to get this right..

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    thanks a bunch for all this doctor briggs! amazing
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    Last edited by Mister Janchichan; March 16th, 2013 at 11:00 PM.
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