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  1. #136
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    Dr. Briggs, This has made me realize that I know absolutely nothing about color( in terms of realistically representing an object).
    Firstly, the uniform saturation principle boggles my mind because they images with the half lights having a higher chroma do indeed look more " realistic" to me than the spheres having uniform chroma throughout. I may even be using the wrong word- from what I can decipher from your text, chroma is the extent to which a hue is farthest from grey, correct? and saturation is the purity of the hue? I have a hard time finding the difference between those definitions and I have read that page about 4 times over. Also the image you have of a painting where you attempted to create a more " realistic" sphere of her skin tone seems infinitely less realistic than what I see in the painted image.

    Also, related to this, I have always been told that the shadow will be of a complimentary color to that of the light, which you say is not true. Reading your text almost leaves me to question that I see color right at all. This may perhaps make sense, as random internet color tests have told me that I may be partially color blind. I don't really know how trust worthy these are because they diagnose that I am partially red/green color blind and I have never noticed seeing something grey, or of a different color that someone has told me it is actually different.

    If you have read all that and still don't know what I'm asking, which I would completely understand- I would like a more simple description of how light , and how progressively less light, affects the perception of a color of an object.

    The sight is very informative- if only I could wrap my head around it!
    "A drawing is not necessarily academic because it is thorough, but only because it is dead. Neither is a drawing necessarily academic because it is done in what is called a conventional style, any more than it is good because it is done in an unconventional style. The test is whether it has life and conveys genuine feeling."- Harold Speed
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  3. #137
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    Thanks for the input, The Pariano

    The whole site is in need of an update, which I'm going to start posting soon. It won't make it any simpler, but hopefully parts of it will at least be clearer. In particular I'll make it as clear as I can that, while the uniform saturation principle describes the underlying pattern, the final effect is modified by reflections of the environment, and also by the adaptation state of the eye.

    The flesh coloured sphere may not be one of my finest efforts, but even so I find it hard to see the portrait as being, say, more easily mistaken for a photograph.

    Regarding saturation vs chroma, I'm told that Figure 9.8 on this page helps:
    http://www.huevaluechroma.com/093.php

    The light in shadow zones typically does appear the complementary color to that of the main light - I'm not sure what I said that made you think I thought otherwise.

    Finally, colourblindness exists in all degrees. If the classic Isihara tests indicate a problem that otherwise goes unnoticed, then you probably have only very slightly anomalous vision. They are widely available on the internet, e.g.:
    http://colorvisiontesting.com/ishihara.htm
    http://www.premlobo.com/eyetest.swf
    More sophisticated tests have been developed more recently that pick up some deficiencies that Isihara misses, but I don't have any links offhand.


    David

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    To anyone in Sydney - I'm giving a public lecture at the Art Gallery of New South Wales this Friday 1-2 pm on "Colour and light in the work of Rupert Bunny", in connection with the Rupert Bunny exhibition. Free, all welcome - please say hi if you come along!

  4. #138
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    This is so helpful! Thanks so much!

  5. #139
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    I'm desperately trying to banish the amateurish "chalky" look of my paintings and your website is a boon...inasmuch as I can decipher. I haven't yet been able to posit any rational questions yet about what is perplexing me. I think I will try your spheres in photo environments exercise, I imagine that will help me see what it is that I truly don't understand. Thank you so much for the invaluable resource that is 'The Dimensions of Colour'.
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  6. #140
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    Although a tough read, the site is the best resource on colour I could find as a beginner. After re-reading things and making notes, things are starting to sink in. I don't know if you still reply to questions, but I would appreciate it if you could point out any errors in my understanding of specular/diffuse reflections:

    1. Every surface can be considered as reflecting diffuse and specular light, where the relative amount of each is dependent on the material of the surface.
    Diffuse reflection of light gives the object its form/colour, specular reflection of light is an image of a light source.

    2. Diffuse reflection of light by the environment (or any object) is a light source for another object (where that object again reflects that light both as diffuse and specular).

    3. Specular reflection results from light that is unchanged by the object and is an ADDITIVE mixture of the colour of the reflected light source and the colour of the reflected diffuse light from the specular's location (following the angle rule).

    Considering the picture below (numbers correspond to brightness levels gathered using color picker).
    The highlight is very bright, thus drowning the diffuse reflection at that location and keeping the colour of the light source.
    However the diffuse reflection of light by the white paper is a weaker light source, so the colour of its specular reflection is an additive mix of diffuse reflection of light from main light source (light side) + diffuse reflection of light from white paper + specular reflection of light from white paper.
    The diffuse reflection of light from the white paper will be strongest close to the paper and diminish as the surface moves away from it in an upward direction. Thus depending on the relative contributions of these three components, the colour of the specular reflection of light from the white paper will vary across the surface of the sphere and will not be same as the colour of its source (the white paper).

    Attachment 957685
    Image source:www.huevaluechroma.com

    QUESTION 1: Why is the brightness of the paper lower at the back of the sphere compared to the front (80+ vs 65)?
    (front = sunlight through a window, back = ambient light in the room perhaps?)

    QUESTION 2: Specular reflection of light from the cast shadow is the same colour as the cast shadow? (as diffuse reflection of light from the cast shadow should be quite weak?(originating as diffuse reflection of light from ambient light))

    QUESTION 3: You stated that the location of the highlight "is always seen somewhere on the line between the point facing the light source and the visual center of the sphere". With the visual centre do you you mean the actual center of the sphere (see picture)?

    Attachment 957709

  7. #141
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    briggsy@ashtons Your website was incredibily helpful to me, quite difficult actually but it made me realize the complexity of the subject and it gave me some technical parameters to evaluate and choose colors.
    I'm now trying to merge informations from your site with those from Jason Manley's color theory lesson, who has a less technical and more emotional approach.
    Any opinion about if and how the two sources can complement each other?


    dragonfury where did you take that picture? That place looks familiar to me... Is it Ferrara??
    Last edited by revenebo; April 25th, 2010 at 08:02 AM.

  8. #142
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    Quote Originally Posted by D.C. View Post
    Although a tough read, the site is the best resource on colour I could find as a beginner. After re-reading things and making notes, things are starting to sink in. I don't know if you still reply to questions, but I would appreciate it if you could point out any errors in my understanding of specular/diffuse reflections:

    1. Every surface can be considered as reflecting diffuse and specular light, where the relative amount of each is dependent on the material of the surface.
    Diffuse reflection of light gives the object its form/colour, specular reflection of light is an image of a light source.

    2. Diffuse reflection of light by the environment (or any object) is a light source for another object (where that object again reflects that light both as diffuse and specular).

    3. Specular reflection results from light that is unchanged by the object and is an ADDITIVE mixture of the colour of the reflected light source and the colour of the reflected diffuse light from the specular's location (following the angle rule).

    Considering the picture below (numbers correspond to brightness levels gathered using color picker).
    The highlight is very bright, thus drowning the diffuse reflection at that location and keeping the colour of the light source.
    However the diffuse reflection of light by the white paper is a weaker light source, so the colour of its specular reflection is an additive mix of diffuse reflection of light from main light source (light side) + diffuse reflection of light from white paper + specular reflection of light from white paper.
    The diffuse reflection of light from the white paper will be strongest close to the paper and diminish as the surface moves away from it in an upward direction. Thus depending on the relative contributions of these three components, the colour of the specular reflection of light from the white paper will vary across the surface of the sphere and will not be same as the colour of its source (the white paper).
    Hi D.C.

    You are a bit of a master of the tough read yourself, but that all sounds like you're on the right track, as long as you keep in mind that the phrase "the colour of the specular reflection" has two possible meanings that you need to stay clear about: it might mean either (A) the overall colour of an area where the specular reflection is the most conspicuous component (as in that last sentence), or (B) the colour of the specular reflection seen as a component of the appearance at that point.


    Quote Originally Posted by D.C. View Post
    QUESTION 1: Why is the brightness of the paper lower at the back of the sphere compared to the front (80+ vs 65)?
    (front = sunlight through a window, back = ambient light in the room perhaps?)

    QUESTION 2: Specular reflection of light from the cast shadow is the same colour as the cast shadow? (as diffuse reflection of light from the cast shadow should be quite weak?(originating as diffuse reflection of light from ambient light))

    QUESTION 3: You stated that the location of the highlight "is always seen somewhere on the line between the point facing the light source and the visual center of the sphere". With the visual centre do you you mean the actual center of the sphere (see picture)?

    1. It's just that the surface to the left of the sphere is further from the main light source.

    2. Yes, if you mean the colour of the specular reflection in sense B above; no, if you mean it in sense A (if it was a red ball, for example, there would be enough light reflected from the tabletop alone to show the local colour in this area)

    3. I was thinking of the centre of the (circular) visual shape of the sphere in the picture plane, though of course this lines up with the physical centre of the sphere.

    Hope that helps!

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  10. #143
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    Hi revenebo

    Very glad you like the site! I'm afraid I didn't see Jason's colour theory lesson, which by all accounts was excellent, but if there any particular issue that is confusing you I'm happy to try to help.

  11. #144
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    Thanks briggsy@ashtons for your reply. You're right that the wording of my post was quite confusing, I had trouble understanding it after re-reading it again :p, sorry about that.

    1. It's just that the surface to the left of the sphere is further from the main light source.
    Is this because the rays of the main light source are not parallel to each other (light source is not a point light source)? As I understand it, the brightness of a surface facing a light source with parallel rays (like the sun) should be uniform across that surface and vary depending at what angle that surface is facing the light source.
    Of course if the surface is big and its farthest point facing the light source is much farther than its closest point to the light source a noticeable difference would occur?

    2. Yes, if you mean the colour of the specular reflection in sense B above; no, if you mean it in sense A (if it was a red ball, for example, there would be enough light reflected from the tabletop alone to show the local colour in this area)
    Sorry, yeah I meant B. I was actually thinking about how the brightness varied in that region and what influenced it.

    Generally, how does the total light reflected of other objects behave as a light source? For example, in your picture, will the diffuse reflection from white paper (tabletop) illuminate the sphere uniformly, will it decrease as the surface turns away from the paper (like with a regular light source), is it strongest closest to the paper? Also does specular light reflected from an object contribute to illumination of other objects (with specular light I mean the part of light reflected at any point on a surface that follows the angle rule).

    These questions arose when I tried painting a simple red cube in photoshop. I couldn't figure out how the ground (white canvas, e.g. white paper) would influence the lighting of the cube and how a potential specular reflection of the ground (white canvas) would look like: uniform in brightness across the surface of the cube or decreasing in brightness from bottom towards the top of the cube.
    Last edited by D.C.; April 27th, 2010 at 08:44 PM. Reason: grammar

  12. #145
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    Quote Originally Posted by D.C. View Post
    Of course if the surface is big and its farthest point facing the light source is much farther than its closest point to the light source a noticeable difference would occur?
    That's it. The intensity of light falls off predictably, according to the inverse square law. With a small light source close to an object, this gradation is very evident.

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  14. #146
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    Yes, the main effect is the roughly inverse square fall-off of light flux with distance; but the decreasing angle of incidence of the light rays to the surface, which I think D.C. was suggesting as the explanation, is a distinct though secondary factor.

    D.C., to answer the second part of your question you need to understand that the inverse square law applies precisely only to a point source of light; with larger light sources the fall-off is slower, and at the theoretical extreme of a wall of light extending infinitely in all directions, it turns out that there isn't any fall-off of light with distance. (You can demonstrate this by bringing up a white page on your monitor in a darkened room, and observing the minimal fall-off of light on objects up to a few cm from the screen). So you would expect little fall-off of light with distance from the table top on the vertical faces of your cube, whereas you do see it on objects like the sphere that curve away from facing the table top.

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  16. #147
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    briggsy@ashtons no issue in particular, it's more about a general sense of disorientation between a "mathematical" approach and an emotional approach based on eyeballing, taste and experience given by exercise.
    I've seen many great artworks, both traditional and digital, that are quite off if compared to the mechanics of light and color you explained and yet they look awesome. In particular it looks like saturation of colors is subject to personal taste and choices.
    I usually try to stick to your instruction when painting (digitally) but, assuming I apply them correctly, I feel that sometimes the result is a little bit boring, in particular in works from imagination. Can the technical parameters be stretched or overlooked in order to convey mood and emotions without screwing up a painting? To what extent?

    PS I know it's a vague question but as I said I'm a bit puzzled by all the info about color theory I'm assimilating...
    Last edited by revenebo; May 2nd, 2010 at 06:16 AM.

  17. #148
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    I think its's a valid question. To me, theory is not there to tell you what to do, but to help you to do what you want to do. Take anatomy for example - just because you understand anatomy, it doesn't mean you can only draw "boring" accurately-proportioned humans. Artists who understand anatomy can draw better monsters, aliens or even spaceships than those who don't, because they can use their knowledge in the service of their imagination and emotion.

    That's how it should be with light and colour. Certainly if you are trying to get a vivid sense of lighting and atmosphere, whether from life or from the imagination, then there are some relationships that you need to get right. But you are free to play with these relationships creatively as well as to report them objectively. To give two examples that are only just a beginning, you can obtain very beautiful effects by accurately transposing those relationships to a very limited tonal and/or colour range, or by transposing the shadow colours to suggest the effect of simultaneous contrast. Obviously this is a step beyond the basic theory, not a step short of it.

    By the way, I'm not at all opposed to eyeballing. As I say somewhere on the site, I think eyeballing rather than mathematical precision is generally sufficient for painting if you understand the relationships involved. All of the spheres in my diagrams for the site were painted by eyeballing the fall-off of light rather than mathematically calculating it.

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  19. #149
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    Hi,

    I just wanna say I have read the colour theory stuff on your website.It is a little confusing to assimilate all those stuff but I am slowly getting it and it has improved my knowledge on colour.But I am a little confused cause I am normally into 3d stuff.All I do is model stuff,add the texture and set up my light,hit the render button and voila!!!I get my artwork.
    Let me see if I am getting this right:
    Lets say I have a sphere and I decided to give it say a red colour,towards the light,you will probably have 4 tones:shaded part(desaturated)dark red----half light(lighter dark red slightly desaturated)---full light(saturated red)----highlight(white).

    Right?I understand some people do grayscale but that ain't working for me.I would have drawn a sphere but I am too busy to do so.Wonderful thread,keep it up,briggsy@ashtons.

  20. #150
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    First post on this wonderful site! I just read thru the above color theory principles and added more insight to my rudimentary understanding. Thanks for all the input!

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