Speculars, radiosity, etc.

[Prometheus|ANJ]

I'm slowly slowly reworking my tutorial. Here's some 'illustrations' (eherrm) mainly on skintones (as I like them). There's gonna be some text to go along with it too, but perhaps it's pretty self explainatory?

http://w1.485.telia.com/~u48508900/misc.jpg

image broken, please view prom's website @ http://www.itchstudios.com/psg/art_tut.htm

[Jane Radstrom]

This is very neat! I've never seen an expalination/ description of these aspects of color. I'm really excited to see the whole thing when it's done. Most of it does seem well explained already, though some of the writing is rough to read.

[DragonGX]

Thanks for the tutorials, very helpful! I like the one in your sig too. Hopefully we will see more tutorials from you!

[Main Loop]

real nice tutorial!

[davi]

way to go prom :]
you should include a reference for people to try to paint and learn from. It's really hard for someone to learn these tips without absolute focus on them.

[gekitsu]

hey, is this for the tutorial in the works you told me about in irc?

that's going to be really great, judging from what you get across with just a few illos.

thanks man, for all the work you put into this

[Prometheus|ANJ]

Yeah I should snap some photos I guess. I dun wanna violate any copyrights. I could provide just urls though.

[stephen]

cool prom, thanks.
one crit tho would have to be "the eye has a very limited value range" its actually the other way around, our mediums (or media) have a very limited value range, and cannot produce exactly what the eyes see, that's why its usually split up into ten or less. etc etc etc etc etc..

anyway, good job, its very simple and colorful!

[gekitsu]

stephen: i think what prom is referring to is the kind of "auto-calibration" the human eye has, always picking a spectrum width that provides the best level of information.

if you are focussing on seeing detail in the sky (in proms small example), you will see brightly lit clouds, you'll roughly see where the sun is located etcetera... but you won't notice any detail of the tree, since its values are a good bit too low for the chosen calibration. if you focus on the tree, you'll lose detail of the sky, as the whole sky is a good bit too bright for values that fit into the value spectrum of the tree.

basically, this is a mind thing, not an eye thing.

[Prometheus|ANJ]

Yeah, the brain does a lot of things with the image from the eyes before our 'awareness' recieves it.
It sets white balance by using surfaces that are assumed to be white. It sets exposure levels for individual objects, producing a false image with local colors and values everywhere. It also unwraps planes and surfaces in pespective, making them flat.
This makes it difficult for us artists since we have to backwards engineer whatever the brain does. Kids often draw stuff unwrapped, and always draw stuff in their local color.
Some artists go back to drawing stuff as the brain wants us to see them, like wierd picasso perspective, or impressionistic dazzling colors and values.

I heard somewhere that we can only read/see/concentrate on a spot the size of a thumb an arm length away. The rest of the image is blury and perhaps under the command of a more instinctive the part of the brain that just scans for moving stuff or familiar shapes. The brain can also fill in details we assume are there, like near the blind spot or at the edge of the image.

[krAtul]

i lub you prom :P

#k

[PhilHolland]

A guess that this is the best place to post this.

Prom, your previous text tutorials are worth a lot to me. After reading those and a few things prior to that I have been much more aware of the world around me.

I have a feeling that I was following the right path, but then I saw your tutorial and a handful of other things that really opened my eyes to the world of color.

For instance I knew about radiosity, but never implemented it very well in my artwork because I never really observed it that closely in the real world.

Nowadays, it is much different for me.
I look at everthing. I try to see as much as I can at any given point with the hopes of catching something new that I never knew before.

Strange enough. I do a lot of photography and if you look at my last two years worth of photos you'll notice a dramatic improvement. I now focus a lot more. I try to take what I see through the lens and apply it to my art work.

Not to get too mushy....

Just wanted to say thanks and keep up the good work.

Phil

[Jeff Gran]

Thank you for this. It is self explanatory and makes me want more pictures and diagrams, no need for text. the captions are enough. You obviously know what it's about and I await the day that I understand as much.

[needOptic]

this is awsome... I lurk more than I post, but this is EXACTLY what I'm trying to learn more off right now.

wonderful, thanks again!


now all I need is to print out your tut's so I can stack em in my "notes" folder. :D

[Prometheus|ANJ]

I'm glad you like them. I learn a lot myself from writing them cuz I'm forced to formulate things consistantly.

Here's a really wierd example though:

Light reflection works just like... tennisballs bouncing of ...rocky asteroids... how they bounce away depends on the incoming angle, surface angle and how bumpy the surface is (I'm ignoring subsurface scattering and refraction). If the surface is smooth the 'bounce-away' angles will be very easy to predict. If the surface is very bumpy, the tennisballs will scatter away in all sorts of directions.

The intensity of the light depends on the number of tennisballs that enter our eye.

You get a specular on a gloss sphere because the tennisballs can only bounce into your eye if the surface angle is correct, and since a sphere is curved there's only one point where the angle is correct. Even if the surface angle is almost correct you won't see any light from there.

On a more bumpy sphere, chances are that a few tennisballs hit some bumps a bit away from the specular point and thus manages to get the right angle to enter your eye. A bumpy sphere will have a less pronounced speculars because of the bumps randomizing the bounce of the tennisballs, in return, we'll get too see parts of the object we wouldn't get to see otherwise.

That's why gloss object often have flat values and a few specular highlights popping out, whilst a dull (bumpy) object doesn't have any speculars, but appears more volumated cuz more light from the more obscure angles manages to find its way to our eyes. But the main shapes of the object is still important cuz the bumps can't change the bounce angle too much. Don't forget that here on earth we have lots of ambient light bouncing around too, cuz we have so many objects here the light can bounce off. The effects of light are probably easiest to observe in a dark room with a single spot lightsource.

But even something dull like cotton cloth have speculars. I stretched my sleeve out with 2 fingers (marked by dots) and took two pics from different angles.
http://w1.485.telia.com/~u48508900/cottonspecs.jpg

[DragonGX]

How do you get the reflected color (I'm talking about the surface that is being hit with color, IE: the blue reflected color on your sleeve) when you paint digitally? I think I could mix paints to get the correct colors easily, but I'm having a really tough time getting good colors on the computer. Also is the reflected colro the same temp as the surface color that its coming from?

I hope you understand what I mean, I have trouble writing this so its esaily understandable!

[Prometheus|ANJ]

well, if you have the color from the monitor, which appears to be cold white, and the color of the sleeve which is dark brown-ish, then you colorpick the sleeve color, drag up the blue slider a bit, and the green and red just a tiny bit.

If the light from the monitor is strong, then drag up the sliders more. A lightsource will never darken what it 'hits', which might happen if you just mix colors with opacity. In the case with this sleeve and monitor, I would probably be lazy and paint the sleeve dark, then mix a bright cold color into it with opacity and colorpick a color that feels right from that. That only works cuz the sleeve is dark though, and thus I don't risk to make it darker.


You can set the colorpicker to 5x5 average, colorpick the lit sleeve, set the airbrush to difference, paint on the unlit sleeve, and thus you get the difference color, which is 44,43,65 in RGB (varies a lot, but it's basically a dark cold grey). Then you can colorpick, undo the stroke, and set the brush to screen and paint over the dark sleve, and you'll get pretty much the same light on it as on the lit one.

[gekitsu]

el promerinjo
you say you modify the color for the reflected light via rgb sliders. do you choose most of your colors via sliders or do you use them for modification only?

asking just out of curiosity... :)

[Prometheus|ANJ]

I use the RGB sliders or I colorpick from my own painting (alt key in PS). If I want to make a spot more yellow for example I can just colorpick and pull up R and G and paint over with the new color. That or I quickly make a yellow color with the RGB sliders and paint over the spot with opacity.

Mostly though, I pick colors from different spots on the canvas and use the paintbrush on opacity (60-70%) and dab/colorpick multiple times until I get the color I'm after.

[benzo]

Prom,

Your tutorials have been very helpful to me. Thank you for your generosity in sharing them!

[gekitsu]

thanks prom.
it just occured to me that using rgb sliders is a quick and dirty way to control if the color im painting could actually be there. (in relation to light color, etcetera)
thanks for the head up :) no go get back to work on that tut ;)

[behemot5]

a lot of people tell me about complementarity of the colours of light and shadow.....what is wrong , what is right?????

[DragonGX]

Usually the shadows of thigns are the complement to the color of the object. So if you're painting an orange ball it'll have blue shadows, same goes with light sources..

You also have to think about the temperature of the shadows.. I think cool colors have warm shadows and vice versa..

someone can correct me if I am wrong.

[Roam]

I agree about the photographs, they do add alot. Also you might wanna use some of the old masters's work to reflect your examples (no worry about copyright since they're dead!)

[vfxart]

I like the initial image... but I don't agree that the eye has a very limited value range. It's actually incredibly extensive, but we have a difficult time judging values next to each other because we don't often focus enough on one specific area and teh illusions of value play too quickly. It's the old trick where a neutral grey square in a light field looks darker than the same grey in a dark... the trick is to slow down and really study the value changes, isolate them if we can.

You may also want to mention something, as it applies to painting and illustration, about the need to keep two distinct realms of light and dark going and the fall-off of various light types. I think that will help some things sink in.

Still and all, this is a sweet page!

[imager777]

The whole oversaturated orange/red color being caused by blood beneith the surface thing, bothers me. Blood is blue, until it comes in contact with air. Veins under the skin are blue. I think something else causes the oversaturation. I've been wrong before though.

[2byts]

if i remember correctly from science class....arteries and capillaries are read because the blood is loaded with oxygen....and the veins are blue because they dont have any oxygen (but a load of garbage)

[Elwell]

Originally posted by imager777
Blood is blue, until it comes in contact with air. Veins under the skin are blue. I think something else causes the oversaturation. I've been wrong before though.
And are once again ;). Check here (http://www.straightdope.com/mailbag/mbloodrd.html), for example.

[imager777]

I feel so edjumicated now. Thank you for clearing that up for me. When I was younger; I, along with everyone else in my biology class, was actually taught that blood was blue. Damn uneducated teachers...

[cateaic]

That was an awesome tutorial..it helped alot!
I dont think we can get enough skin tone tutorials. In fact, if anyone here has any other skin tone tutorials please share!!! =)

[Beer Baron]

Thank you for taking the time to put this together, Prom. Very insightful and helpful. The tennis ball analogy really helped.

Can you recommend any art books that deal with this topic in-depth? Most of the books I've found deal primarily with mixing colors a certain way and not exactly explaining why. I'm mostly looking for something along what you talked about: what our eye can see, the dynamics of light, etc. Might this book be in the 'Science' section?

Color theory is an area that confuses me the most. Your tutorials really help clear away some of the clutter. Thanks.

:)

[Prometheus|ANJ]

THeree's some blue on skin too. Frazetta paints it a lot (hips, boobs). Light can also pass right through skin and make it red/orange, you've seen this effect on ears and fingers maybe.
Anyhow, this is just a part of a big tutorial I'm working on. I'll try to cover everything I know in it, including light falloff and stuff. I often fall into the trap of over-volumating with shadows and hilites. When I look at stuff in real life I notice how flat values can be. Sometimes it's just a flat shadow and flat light even though there's lots of bumps and knobs on the surface that would look neat volumated out more.

As for books I don't know of any. Maybe loomis?

[funshark]

wow!
I can't wait to see your big tutorial, Prometheus !!
:jump1:

[Marcatili]

Hey Prometheus,
I really appreciate the tutorial as well, although unlike some of the others I didn't find it all self-explanatory necessarily.
Most of it I was ok with once I looked over your diagrams a few times.

I didn't understand the reason for some of the diagram elements, for example where you have the tree which is shadowed by the sun and then a brighter or maybe diffused sun where the tree is not shadowed. I understand the middle diagram where the sun is shadowed because of the strong back light of the sun but not why or how the bottom one worked.
Also, next to that there is a tree with a sun beside it and a blue line- does the blue line indicate a range of something or is it a cross-section? I wasn't sure...

Like I said, I understood most of it but I suppose the other main thing is I'm the kind of person that needs to know why things are, not just that they are. Or maybe I'm just a lunk-head...

anyway, thanks for the great tutorial, I do think it requires a basic level of understanding light and colour theory but that's fine :)

thanks again

[naz]

great illustrations and especially thanks for your "How I paint in Photoshop FAQ", together they really give a great insight!

on the illustrations sheet, the section with the ambience right/wrong, I understand now what it means, but first it was not imminently clear to me.

thanks again for sharing!

[gekitsu]

expat: the three illos with the sun and the tree basically read like that:

since sky and sun are of significantly higher value than the tree, and the eye/mind tends to simplify what you see in simple value patterns with a very narrow value scale, you will never see something like the topmost illustration.

your eyes would either focus on the foreground values (the tree), but this would knock both sky and sun "out of range", as seen in the lower illustration.

if you focus on the background color (sky), you will see the difference in value between sky and sun better, because you adjusted your value key to this particular part of the value scale. the tree, however will be knocked out of range then and appear as a dark silhouette, as seen in the middle illo.

[Groover McNab]

This is great! Thank you!

[Grooveholmes]

Ah yes...

Some of the best golden gold ever to be gold.

[sandu22]

About the skin.. not only Franzetta.. also Boris , even Dali..anyway is a good trick. :chug:

[AmadorL]

Hey Dude when are ya going to get to those unfinished tutorials on your website? looking forward to seeing them.

-A

[fabyan4u]

:evilbat: it is the most explicit thing i've ever sow.now i understand the color combination thing

[Kress]

Prom, I was just thinking to myself, oh man, I better get to some practicing, I'm getting way sloppy. And lo and behold, here you come with this packet of goldness. Awesome.
I've been painting bilites by picking the light color and slapping it right on top of things. How brutish :(
So uhh, how about some more matte/flat material information???
Thanks so much for posting this. Hopefully I'll be able to apply it.

[herbesahne]

It's a really interesting topic, I was wondering if there are books on this subject ? And also do you think it's a good idea to study light/colors with a 3d program (but then again wich renderer..)

[RefrigeratorCo]

You posted some interesting stuff man but I think I need some words to go along with the pictures.

[Pesmerga]

Awesome tutorial! but your hand writting is terrible, lol.

This may sound pretty stupid, but... I'm not sure I understand this one:

http://img.photobucket.com/albums/v442/Luis_AV/Miscellaneous/example.jpg


And about your reflecting sleeve... I'm wondering:

http://w1.485.telia.com/~u48508900/cottonspecs.jpg
That red in the lower part... is that your cam reflecting it?

[Gator]

that is a really useful explanation on how light bounces around!

From what I understood, the red and green dots show where Prometheus was pulling the sleeve with his fingers. He used a cotton sleeve to show how a coarse fabric also has specular properties (in this case, bouncing off light emanating from the screen). At least thats what I think it is!:P

Though I do have my doubts on that first picture you posted, Pesmerga. I don't fully understand that one either. :S

[At_the_Gates]

I think that the first pic shows how the sky (or blue things) reflects on
different surfaces/colors... it kinda makes the skin a bit blue, but when
you have some black clothes, it kinda "sucks" in the color. heh... :\

[hamsterdance]

Thank you for this tutorial. This was very helpful for me.

[IvanDashSmith]

Great stuff Prometheus. I downloaded this off of your website some time early in the summer, and made it my desktop which helped a lot in my illustration class. That and a lot of your work I showed my teacher inspired him to assign a digital painting. Keep slappin down the knowledge, and update your website dood. :wink:

[nonie]

This thing made me have one of those "oh my god, duh" moments. The little "can't get darker" note - suddenly radiosity makes just a little more sense. Thanks for posting it, Prometheus :)

[Judy Warner]

is there any way to see the pictures on this thread--all I see are the dreaded x's.. ????? Judy

[Elwell]

is there any way to see the pictures on this thread--all I see are the dreaded x's.. ????? Judy
http://www.itchstudios.com/psg/art_tut.htm

[Judy Warner]

lots of very, very good info now that I can see the pictures! Judy W

[Farvus]

well, if you have the color from the monitor, which appears to be cold white, and the color of the sleeve which is dark brown-ish, then you colorpick the sleeve color, drag up the blue slider a bit, and the green and red just a tiny bit.

Arghhh. Why didn't I thought of using sliders before :P. I was recently painting a lot with natural media and using only primary colours. In Photoshop there are CMYK sliders so I could learn a lot by using these.

Thanks for writing this Prometheus !!!

Farv

[tanz]

the pics gone missing...

[Elwell]

the pics gone missing...
http://www.conceptart.org/forums/showpost.php?p=545268&postcount=52

[amit3d]

Really a very good link. Thank you.

[626elemental]

Amazing! The best tutorial I've seen in years!

[George Abraham]

I think it could be a good idea to build a material library in either visual or written reference to build some sort of databank about how different materials behave in light.

I have scanned the net for something that other artists have done perhaps but I couldn't find any.

Maybe one of the fundi's here could sell off a collection of sphere's and cubes made from different materials with notes on what effects they are paying attention to.

Some 3D apps have nice libraries but I feel a painted out version will be much better and there’s so much effects to explore.

[Natalyah44]

That was an awesome tutorial..it helped alot!
I dont think we can get enough skin tone tutorials. In fact, if anyone here has any other skin tone tutorials please share!!! =)

Glad to read such a nice piece of information.
This is exciting news. :girl:
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[AlexanderSkyy]

The information you presented is decently informative and thought out, and I congratulate you on compiling this. However, there is a statement here; or rather a thought, that is inherently flawed and out of principal almost stopped me from bothering to read this.

"I believe there is logic behind why a picture works or not. I also believe that humans are meat machines, and that one day computers will be able to emulate humans and what we do."

Yes, there is a sort of science to composition, colours, lighting, and so on. It has been recorded and studied by the masters for ages. Yes, you can program a machine to produce results within the tolerances you set for it using those guidlines. But that is the end of it. Humans introduce an intagible and imperfection into the equation; it's called beauty, and it's something a non sentient machine can never prodcuce. You can have a machine produce a 'perfect' image with 'perfect' composition, lighting, colours and forms, and set it next to an imperfect image produced and processed through the human heart and a 4 year old could tell you which is better. A machine can only make marks on a page. It cannot create. It's images may nice, but it cannot understand the why, it cannot concieve the image; place emotion and thought into those marks to turn them into something meaningful.

Side note: You do not very clearly nor accurately explain Hue, Value, and Saturation clearly when covering gradients and shadows; this could lead to alot of confusion to less well read art students. You consistently interchange saturation and value, making horribly incorrect statements. And it's diffusion, not diffraction. I could go on, but through much strength of will I digress. Since alot of people read your thing since it's a sticky, I strongly urge you to revise.

[Juki]

This is truly a wonderful tutorial and you can tell that a lot of effort has been put into it. I think I'll be spending some time chewing all this info, thank you very much.