The Dimensions of Colour - a colour theory discussion thread

[briggsy@ashtons]

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."

[briggsy@ashtons]

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.

[Mister Janchichan]

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..



thanks a bunch for all this doctor briggs! amazing

[Mister Janchichan]

hey people, i want to share something with you, would be nice to hear about your experiences;

after reading though the hole thread, i got a way more better understanding of how color really works. sometimes in observation in nature, its hard to tell at first where desaturations and stuff come from, so after reading all this yesterday i was feared it could have killed my ability to workout concepts from (color)scratch. i was (partly self-)taught lot of the stuff in color-theory another way, that changed my thinking about what i see and what im doing completely.

for example, before understanding it better, i had judged a bit different on seeing and applying colors (ah, there is that light, that causes desaturation cause its so bright yaddayadda)... now ive to switch to a new thinking, have to explain the colors with another concept in mind (the 2nd light falling on my object causes desaturation because its shares lesser wavelengths with the object/primary lightsource - or so)

so brave as i am, i tried, just after slept over it all (im quite sure i dreamed of colorjudgment and behaviour) and tried it in one of my creative processes of creating a concept, in this example by doodling with harmonic and complimentary colors to establish a pleasing colorscheme as a good starting point for a picture.

one guideline helped me much: its all about how you justify(is it the right word?) your choices in color, how you explain what happens with it in relation to the color-theory, so this gives me the freedom to know where to seemingly breaking the rules, and make decisions more for aesthetics than color-theory.

this was one of my fears i had before all this, that i could "unlearn" to make my colordecisions and choices.

by "breaking the rules" i mean for example how i would explain desaturations where normally shouldnt be desaturations - i would just imagine the material, for example stone, is much more chalky on some faces, on some its more altered through nature (more green/red) and stuff like this.

so one thing stays quite true through this: the better you get - the better your decisions will get

[Mister Janchichan]

HHi, its me again i need some help on reflected light; how can i think of light reflected by sourrounding Objects, how Do i Kind of measure its desaturation it would probably cause? For example, im in a Hotelroom right now and heres a mirror with a warm Orange border. On the side its facing the only lightsource its saturated, on the front facing the room its desaturated, there is a grey, slightly blue wall on the opposite. Are such objects like the wall for example reflecting light that can cause this? If the wall was white, it would reflect the light in a purer state and Not much would Change right? I just need a hint how to think about This Situations. Maybe the sum of the light reflected by the room and its Objects itself - warm furniture - warm light; thanks, i hope This thread is still alife

[briggsy@ashtons]

MrJ, the thread is still alive, but if you have any questions you should at least post a photograph of an actual situation in which the question arises or, even better, a photograph plus an attempt at a painting. My answers will be more relevant and quicker if I don't have to struggle to understand what you are asking!

In the pink drapery on the left side of the Bouguereau I see the lightest desaturated colours as silky (specular) highlights, but the less bright desaturated colours read to me as the pale flesh colour showing through the drapery, as if this was slightly transparent. The ochre and purple draperies on the other hand basically follow the idea of strongest chroma in the highest lights, except for some desaturated lightest areas on the purple drape, which read to me as slightly faded patches rather than highlights.

By the way, this thread really just consists of random footnotes to the Dimensions of Colour website, so that's what I'd be encouraging people to reread, especially anyone who hasn't seen the updates I've been posting there since early last year.

[Mister Janchichan]

hey, thanks for the reply, i will study your page further to try answering some of my questions by myself at first

ive read my way through basic of light and shade and it helped me so much to understand specular and diffuse reflection. this 2 points are helpful to understand the desaturation effect and where and why additive colourmixing in relation to objects take effects. i considered materials as clothes, papers and such as in general not able to reflect something specular. but to proof this i can just observe this effect on seemingly dull objects like colored paper in various observation angles.

but one thing is still not clear in my mind - does the amount of possible specular reflection (glossiness!?) have any effect on how strong the pure diffuse reflection is? i think about specular relflection as one of two parts of the full light the object is lit with. maybe 20% will be reflected by the surface (specular) and 80% is entering the material itself (subsurface scattering) and will be reflected in a diffuse way.

if the material is more reflective it would be, lets say 70% specular reflection and 30% diffuse - so the material is lit by a smaller amount of the hole light, which leads to less materialcolor, so the reflected light in additive color mixing would take the lead.

i hope you are getting the point. even if im understanding it step by step its still a bit hard to combine all the truths to one conclusion.

[briggsy@ashtons]

MrJ, I think it's very rare to find a material that had 70% specular reflection and 30% diffuse overall - it's typically around 5-10% specular for most materials except polished metals, which have very high specular reflection and no diffuse. However one common situation where you would get reflection like you describe is looking at a backlit glossy object, where a relatively high percentage of the light is reflected specularly because the light hits the surface at a very low angle, and yes, in that case the specular reflection tends to predominate over the diffuse reflection.

Jamie590, you're very welcome!

[Mister Janchichan]

thanks alot!

i think i got it, with the asumption that the 5-10% are fullest noticeable when observing from the ideal angle, it fades when we drift away as an observer and diffuse reflection takes over in appearance. in this situation the overall reflection should not much be influenced by the specular

does the concept to think of every object as a little mirror misleads me or something? ive got a hard time to think of all angles where light comes from in concepts or when studying photos. it would be way more easier to think of it like: if i put a mirror on the ground on this point, what would it reflect? it would also be helpfull to seperate the diffuse and the specular from each other.

i begrudge you for the freedom with colours you should have while painting

[Mister Janchichan]

i made a simple scene-sketch to proof if i got right what i learned so far in terms of whats happening in my head when setting up a scene, sunset-example:



A - determining a proper atmosphere-colour, slightly purple cause of the following influence Y-YR-R sunlight.

B - White light scattered by water-drops and dust in the atmosphere.

C - determining the hue for a simple ground

D - specified the material of the ground: could be the see-ground, like brown sand, just the water is missing considered the diffuse reflection on the ground from the blue sky.

E - atmosphere layer over the ground and specular reflections of the sky, stronger in the distance cause of the viewing angle

F - a layer of sun and a more dusty atmosphere in front of it. the sunlight has a longer way through the atmosphere on this angle, so more of the blue-light got scattered and is lost in distance, the light left is missing the blues and violets.

G - maybe ive overdone this step a bit..i wanted to show the effect of the red dusty atmosphere on the ground in the distance.

H - thought about what a specular reflection of the sun would look like. on the bottom part of the picture the a weak specular-reflection mixes additive with the diffuse-reflection of the ground.

i hope someone corrects me in case of mistakes

[Mister Janchichan]

ive tried the exercise shown on this thread. it was really challenging. i took this picture last week, it was a grey day on holidays...



A - should be a glossy orange Material. as the skylight surrounds the ball nearly the same on every side the specular-reflection is very even.
found it hard in terms of color-constancy to keep the color-ID. in the shadow-zone there are some dark reflections of the ground, fading away in distance.

B - i find it hard to tell what material could result in such a look, maybe painted wood. due to the lightning-situation there are no big shadows in this scene, so the appearance seems legit somehow.

C - This could be a rubberball. i first thought a highlight is missing, but its swamped by the overall specular dispersion

D - this sphere used to be a marble. im still not sure with the highlight, if its very cloudy there should be no specific highlight, right? but maybe its just the sun behind the clouds showing through just a bit.

F - this should be a very low-chroma-orange cottonball. the mix of the specular-blueish and the diffuse-orange leads to a slightly yellow-bright additive result.


this should be enough for today, gosh

[briggsy@ashtons]

Mr J, sorry, I haven't been around for a while, and for some reason I'm no longer getting email notifications of new posts on this thread. You seem to be basically on the right track, but make sure you do plenty of observation of actual objects in different situations to develop a sense of how the theory works in practice, such as as how strong to make the various component reflections contributing to the appearance. You'll learn much faster if you let nature answer your questions.

--------------------------
This week I posted some new material on historical colour systems on the first two pages of my section on "Hue". With the revisions I've been generally trying to make the site better without making it too much longer, but both these pages are substantially expanded:

7.1 FROM ARISTOTLE TO NEWTON
- Hue before the hue circle
- Newton's hue system
http://www.huevaluechroma.com/071.php

7.2 THE RYB HUE CIRCLE OR "ARTISTS' COLOUR WHEEL"
- Origins of the "artists' colour wheel"
- What colour are yellow, red and blue?
- Itten's colour theory and hue system
http://www.huevaluechroma.com/072.php

The 2012-2013 revisions uploaded so far are now:

Introduction and summary
http://www.huevaluechroma.com/index.php
http://www.huevaluechroma.com/011.php
http://www.huevaluechroma.com/012.php

Additive mixing
http://www.huevaluechroma.com/041.php
http://www.huevaluechroma.com/042.php
http://www.huevaluechroma.com/043.php
http://www.huevaluechroma.com/044.php
http://www.huevaluechroma.com/045.php

Subtractive mixing
http://www.huevaluechroma.com/051.php
http://www.huevaluechroma.com/052.php
http://www.huevaluechroma.com/053.php

Colour mixing in paints
http://www.huevaluechroma.com/061.php
http://www.huevaluechroma.com/062.php
http://www.huevaluechroma.com/063.php

Hue
http://www.huevaluechroma.com/071.php
http://www.huevaluechroma.com/072.php

Next to come: the rest of the "Hue" section...