The Dimensions of Colour - a colour theory discussion thread - Page 10

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  1. #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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  3. #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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  4. #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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  5. #274
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    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

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  6. #275
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    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

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  7. #276
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    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.

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  8. #277
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    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.

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  9. #278
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    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!

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  11. #279
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    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

    Last edited by Mister Janchichan; March 23rd, 2013 at 07:04 AM.
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  12. #280
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    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:

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    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

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  13. #281
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    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...

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    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

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  14. #282
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    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...

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  15. #283
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    Thanks for all the information on your site, Briggsy. I do have some questions, though.

    It's about this page: http://www.huevaluechroma.com/107.php

    You have a chart which says that at an 80 degree angle the light will be 45% strength compared to the full diffuse light, assuming I'm understanding this correctly. If my understanding is right, that means a sphere's surface with a diffuse light at 100% B on Photoshop's HSB should go down to 45% right before it reaches 90 degrees and turns to shadow. Is it right to calculate brightness by multiplying full diffuse light by .45 to get some idea of the light side's brightness range? I just want to make sure I understand this correctly, though it does appear to look accurate from the quick experimenting I've done.

    Second question: is there a similar way to calculate the shadow side of these spheres? Basically, is there a similar relationship that can be determined regarding reflected light between: light cast onto a surface, this surface's value, and the value of surface the light is being reflected onto?

    Lastly, kind of unrelated: you've mentioned in other threads/posts that Lab mode works better for layer effects. Do you paint in Lab only? Do you switch over and flatten, go back to RGB? Are there drawbacks to painting in Lab?

    Last edited by ThereIsNoJustice; November 13th, 2013 at 10:54 AM. Reason: added Lab question
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  16. #284
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    You're very welcome TINJ!

    1. You seem to be interpreting the chart as intended: at 80 degrees the light energy (a linear parameter) is down to 17%, but it's perceived brightness (a nonlinear parameter) is still 45%, and B in Photoshop is a nonlinear parameter. But please bear in mind the provisos in the preceding paragraph that the numbers apply strictly only to a point light source at infinity; for example, the fall off will be noticeably faster for a very close light source.

    2. The situation on the shadow side is much more complicated, as the illumination at any point is the sum of the ambient illumination plus reflected light from every point in the environment. If you imagine you are an ant on the shadow side, the light at that point is the combination of everything that you see.

    I'd like to stress that the best use of these principles at first is to help you to really understand what you are seeing when you paint from life. This will give a much better sense of how to apply the principles convincingly when working from the imagination later on.

    3. The way I'd put it is that the layer modes work quite differently in Lab and RGB mode, so if you do a lot of digital painting it's well worth exploring the effect of those differences. If you want to use a Color layer to colour a greyscale painting without changing the perceived value then this works much better in Lab mode, but RGB mode is generally the one to use if you are emulating phyical effects of light, e.g. superimposing the pattern of light and shade created by several light sources (as in post 271 above). When I paint digitally I tend to go straight to colour, so I don't actually use the Colour-in-Lab mode trick that often myself. I mostly work in RGB mode and switch into and out of Lab mode when needed. If you understand what the modes are actually doing you have a lot more options for inventing ways of doing what you want on the spot.

    -------------------------------------------------

    If anyone posts a question here it's a good idea to email me as well, as the CA notification system doesn't seem to be working for me.

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  17. #285
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    hi there,

    i hope someones still active in here, ive got a problem with light-situations in rooms. there is much indirect light thats bounced through the room, reflected by the walls and objects in it. i dont want to measure everything out exactly, but to tell where something is brighter and how i can determine the overall illumination of a room i need a little help.

    it seems to me that most of the overall illumination of a room that doesnt come directly from a light-source (lamp, window) is caused by specular reflections of light-beams that are bouncing through the room. i came to the conclusion cause it couldnt be from the diffuse-reflection, as the the diffuse reflection seems to have a very high fall-off. if even small amounts of light rays from a direct light-source bounced in this and that direction, that would make much more sense, but i am not quite sure.

    can someone help me out with this? it seems impossible to "just find out", i dont know how.

    thanks!

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  18. #286
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    Mr J,

    Why not just stand in the middle of the room and look? What you see is the light coming from each point in the environment. Chances are most of the indirect illumination is diffuse reflection coming from the ceiling and walls (unless your room is as full of books as mine is!).

    David

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  19. #287
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    Hey briggs you ever thought about adding lighting as a subject to your site? (not a request btw) Like lux, footcandles, etc. could be a nice addition, especially with color temperature etc.

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  20. #288
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    Quote Originally Posted by briggsy@ashtons View Post
    Mr J,

    Why not just stand in the middle of the room and look? What you see is the light coming from each point in the environment. Chances are most of the indirect illumination is diffuse reflection coming from the ceiling and walls (unless your room is as full of books as mine is!).

    David
    Thanks Alot David, i've got One question left for now if you dont mind, its about light in distance. I wanted to paint a scene were Pink glowing cubes falling from the Sky into the ocean, and i wondered how the Color would appear in distance.

    From what i know, Blue light gets scattered as it travels through the atmosphere, so luminated Pink in distance should lose some of its blue light, so it Shifts more to red. But also the light travels through the Blue atmosphere, doesnt it get altered to blue again, like objects in distance? I would paint it just less intense. With that in mind, what Happens to Blue Ort Cyan light in distance?

    I would try that Out, if i just could

    I really treasure your help!

    J

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  21. #289
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    These are the droids you are looking for; http://en.wikipedia.org/wiki/Aerial_perspective

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  22. #290
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    Quote Originally Posted by Mister Janchichan View Post
    From what i know, Blue light gets scattered as it travels through the atmosphere, so luminated Pink in distance should lose some of its blue light, so it Shifts more to red. But also the light travels through the Blue atmosphere, doesnt it get altered to blue again, like objects in distance?
    Blue light is removed by out-scattering out of the beam to the eye, but also added by in-scattering into the beam. But while each additional kilometre of distance adds the same amount of blue light by in-scattering, it removes proportionally less and less by out-scattering. So objects that give off a lot of light show out-scattering dominant up to a certain distance before in-scattering takes over. So white objects at first lose blue rapidly and become darker and shift in hue shift in hue towards the red end of the spectrum

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  23. #291
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    Unfortunately the entire site at the University of North Carolina (ibiblio.org) that hosts my website has recently started giving a malware warning in Google Chrome. Hopefully ibiblio.org will fix the issue very soon, but I'm afraid it's completely out of my control. I'd advise avoiding the site until it's been cleared by Google.

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  24. #292
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    Quote Originally Posted by briggsy@ashtons View Post
    Unfortunately the entire site at the University of North Carolina (ibiblio.org) that hosts my website has recently started giving a malware warning in Google Chrome. Hopefully ibiblio.org will fix the issue very soon, but I'm afraid it's completely out of my control. I'd advise avoiding the site until it's been cleared by Google.
    Tranks Alot for the answer!

    @the malware thing: I ignored the warning, i thought it must be a misunderstanding, a Bit naive D: Hope it will be fine soon!

    Today One question arised while Watching a Video on youtube of a Guy Diving in a dark Deep hole in the ocean. It was completely Black, but when i've painted the ocean from Imagination i had always in mind that the ocean is blue Even in Deep Areals. i thought of some thing like a diffuse reflection of the water itself, something has to make the light visible right? but do i See the light when im lookin Deep Down to the ground but there is no ground to reflect the light? I guess, where no light is reflected from the bottom (too Deep) there is Hardly any light.

    Last edited by Mister Janchichan; December 15th, 2013 at 04:20 AM.
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  25. #293
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    The Dimensions of Colour (huevaluechroma.com) is now all clear on Google. As it turns out there was never any malware on the site itself, the warning was triggered solely by two links back to the hosting organization, ibiblio.org.

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  26. #294
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    Quote Originally Posted by Mister Janchichan View Post
    Today One question arised while Watching a Video on youtube of a Guy Diving in a dark Deep hole in the ocean. It was completely Black, but when i've painted the ocean from Imagination i had always in mind that the ocean is blue Even in Deep Areals. i thought of some thing like a diffuse reflection of the water itself, something has to make the light visible right? but do i See the light when im lookin Deep Down to the ground but there is no ground to reflect the light? I guess, where no light is reflected from the bottom (too Deep) there is Hardly any light.
    I guess the answer depends on how deep you are and whether or not the water is at all turbid. However in your documentary I assume they were using artificial light sources for lighting; these would tend to make a dimly lit environment away from the lit areas look completely black by contrast.

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  27. #295
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    Hi briggs, I have a quick question for you.

    So Light falloff occurs at an exponential rate... now i was reading about color on wikipedia and i found this; (its attached). Now i cant make it out too great what i think it might suggest though is that the P value is either cubed or squared.

    Would this suggest that a light source which is pure red as it falls off loses both its chroma and value (i suppose they are linked) at an exponential rate?

    I guess what im asking is would chroma be linked to light falloff at this exponential rate?

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    I'm pretty new here, so I thought I would give the challenge a shot! These are some photos I found browsing around some landscape blogs. They are all meant to be matte red balls.

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  29. #297
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    thanks alot briggs!

    Quote Originally Posted by Ixyra View Post
    I'm pretty new here, so I thought I would give the challenge a shot! These are some photos I found browsing around some landscape blogs. They are all meant to be matte red balls.
    Hey, it would help to show how the balls local color would look like, your ball seems to be more orange than red!

    greets

    Can someone help me out, i got stuck with why the sky gets more cyan/lighter near the horizon. my assumptions are:

    - around the sun its because of solar glare
    - on the opposite to the sun its because more light is reflected by upcomming dust/haze
    - its cyan because of the reflected sun-light (slightly more yellow) plus the skylights blue

    besides that the sky is mostly blue, it contains always more green then red, why that? because of red gets absorbed by water particles in the air? or green gets scattered after blue, just a smaller amount?

    somehow i got stuck on it

    Last edited by Mister Janchichan; December 27th, 2013 at 07:47 AM.
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  30. #298
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    Quote Originally Posted by Mister Janchichan View Post
    thanks alot briggs!



    Hey, it would help to show how the balls local color would look like, your ball seems to be more orange than red!

    greets

    Can someone help me out, i got stuck with why the sky gets more cyan/lighter near the horizon. my assumptions are:

    - around the sun its because of solar glare
    - on the opposite to the sun its because more light is reflected by upcomming dust/haze
    - its cyan because of the reflected sun-light (slightly more yellow) plus the skylights blue

    besides that the sky is mostly blue, it contains always more green then red, why that? because of red gets absorbed by water particles in the air? or green gets scattered after blue, just a smaller amount?

    somehow i got stuck on it
    Thanks for the help!

    The reason why the sky fades into a lighter color near the horizon is from atmospheric particle scattering. What you're seeing is the Earth's atmosphere moving particles around, changing their wavelengths, and therefore appearing "white/cyan" near the horizon (earth's surface). This is the same reason why when the sun sets, the sky turns orange/purple around the sun instead of just turning gradually dark.
    This is also the same reason why there is more green than red in "sky blue". The color blue is a high energy wavelength, which is shorter and much more easily penetrates the earth's atmosphere. Red is a low energy wavelength and is the longest visible wavelength in the spectrum, making it very difficult to pass through the earth's atmosphere (seen during sunset when the sun is right on the horizon and reds can pass through). All of this also explains skylight because all it is, is blue wavelengths passing through the atmosphere and bouncing off of everything on earth's surface.

    Last edited by Ixyra; December 29th, 2013 at 10:00 AM.
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  31. #299
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    Quote Originally Posted by Ixyra View Post
    Thanks for the help!

    The reason why the sky fades into a lighter color near the horizon is from atmospheric particle scattering. What you're seeing is the Earth's atmosphere moving particles around, changing their wavelengths, and therefore appearing "white/cyan" near the horizon (earth's surface). This is the same reason why when the sun sets, the sky turns orange/purple around the sun instead of just turning gradually dark.
    This is also the same reason why there is more green than red in "sky blue". The color blue is a high energy wavelength, which is shorter and much more easily penetrates the earth's atmosphere. Red is a low energy wavelength and is the longest visible wavelength in the spectrum, making it very difficult to pass through the earth's atmosphere (seen during sunset when the sun is right on the horizon and reds can pass through). All of this also explains skylight because all it is, is blue wavelengths passing through the atmosphere and bouncing off of everything on earth's surface.

    thanks for the detailed answer! the only thing i dont get is, if its so difficult for red wavelengths to pass through the atmosphere, why are they able to pass on sunsets? you mentioned this, but i cant find
    the reason. on sunset the light have to travel through a lot more atmosphere, so it should be even more difficult to pass through..

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    Quote Originally Posted by Mister Janchichan View Post
    thanks for the detailed answer! the only thing i dont get is, if its so difficult for red wavelengths to pass through the atmosphere, why are they able to pass on sunsets? you mentioned this, but i cant find
    the reason. on sunset the light have to travel through a lot more atmosphere, so it should be even more difficult to pass through..
    Good question! I don't fully understand the answer to this either, but from what I've learned this is what information I can pass on:
    The sun is just pure energy, which emits a perfect spectrum. The atmosphere (bunches of particles) prevents a lot of that spectrum from coming through. The color from light we see are also particles that are being emitted/rejected, and not absorbed, from the atmosphere (Hence being able to "pass through"). For some reason that I can't remember but is related to particle emissions, the closer the sun gets to the horizon, the more it allows the red light to bounce off particles for us to see. It's the exact same reason to why we see the white/cyan at the horizon, but the exact science behind it I can't recall. I may be able to find my notes somewhere and post what I've found at some point! I just know it deals with particle scattering.

    Last edited by Ixyra; December 30th, 2013 at 01:10 PM.
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