Art: Speculars, radiosity, etc.

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  1. #1
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    Speculars, radiosity, etc.

    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?

    Speculars, radiosity, etc.

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

    Last edited by davi; August 10th, 2007 at 08:56 AM.
    Jamen jag tror att han skäms, och har gömt sig. Vårt universum det är en av dom otaliga spermasatser som Herren i sin självhärliga ensamhet har runkat fram för å besudla intet.
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  4. #2
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    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.

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  5. #3
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    Thanks for the tutorials, very helpful! I like the one in your sig too. Hopefully we will see more tutorials from you!

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  6. #4
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    real nice tutorial!

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  7. #5
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    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.

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    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

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  9. #7
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    Yeah I should snap some photos I guess. I dun wanna violate any copyrights. I could provide just urls though.

    Jamen jag tror att han skäms, och har gömt sig. Vårt universum det är en av dom otaliga spermasatser som Herren i sin självhärliga ensamhet har runkat fram för å besudla intet.
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  10. #8
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    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!

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  11. #9
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    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.

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  12. #10
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    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.

    Last edited by Prometheus|ANJ; December 23rd, 2003 at 09:52 AM.
    Jamen jag tror att han skäms, och har gömt sig. Vårt universum det är en av dom otaliga spermasatser som Herren i sin självhärliga ensamhet har runkat fram för å besudla intet.
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  13. #11
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    i lub you prom

    #k

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    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

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  15. #13
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    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.

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  16. #14
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    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.

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  17. #15
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    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.
    Speculars, radiosity, etc.

    Last edited by Prometheus|ANJ; December 25th, 2003 at 01:11 PM.
    Jamen jag tror att han skäms, och har gömt sig. Vårt universum det är en av dom otaliga spermasatser som Herren i sin självhärliga ensamhet har runkat fram för å besudla intet.
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  18. #16
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    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!

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  19. #17
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    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.

    Last edited by Prometheus|ANJ; December 25th, 2003 at 07:39 PM.
    Jamen jag tror att han skäms, och har gömt sig. Vårt universum det är en av dom otaliga spermasatser som Herren i sin självhärliga ensamhet har runkat fram för å besudla intet.
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  20. #18
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    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...

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  21. #19
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    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.

    Jamen jag tror att han skäms, och har gömt sig. Vårt universum det är en av dom otaliga spermasatser som Herren i sin självhärliga ensamhet har runkat fram för å besudla intet.
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  22. #20
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    Prom,

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

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  23. #21
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    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

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  24. #22
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    a lot of people tell me about complementarity of the colours of light and shadow.....what is wrong , what is right?????

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  25. #23
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    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.

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  26. #24
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    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!)

    AIM: DEVIANT2002
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    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!

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    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.

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    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)

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  30. #28
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    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, for example.

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  32. #29
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    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...

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    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!!! =)

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