Question about Cast shadows.
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    Lightbulb Question about Cast shadows.

    Let's say that you have an artificial light source that is below your object, like this:

    Name:  castshadowpractice.png
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Size:  28.5 KB

    How can you measure where the shadow should go and how far it goes in that case? I've been searching through some tutorials but can't seem to find the awnser.

    Thanks a lot in advance and sorry if the question is kinda silly!!

    Last edited by Hauteclaire; November 19th, 2012 at 02:31 PM.
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    Well, Seedling has this: http://conceptart.org/forums/showthr...98#post1485598
    I might guess that helps if you have a wall behind the object, but overall I think that might also depend on how strong is the lightsource.

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    Well... how far the shadow goes depends on the light source; if it's going through a frosted glass, the shadow will be very small and fuzzy I assume, but if the bulb is clear glass, then it would depend on how strong the light source is. I'd imagine it would go a lot further than a light source from above, but you should give it a try yourself and see what happens irl.

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    Well...the shadow is going to move away from teh light source? Other than that it depends on the physical setup or situation...teh environment and light teh subject exists in.

    If you are interested in projecting and constructing shadows that topic is generally covered under perspective theory.

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    3D to the rescue!

    Name:  Picture Viewer.jpg
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    (If the light source is narrower that the object)

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    Don't say I have no life, but...

    Block is 10 cm wide.

    Light 5 cm (narrower)
    Name:  5cm.jpg
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    Light 10cm (same width as block)
    Name:  10cm.jpg
Views: 323
Size:  25.4 KB

    Light 20cm (wider than block)
    Name:  20cm.jpg
Views: 313
Size:  25.6 KB

    Who needs Call Of Duty, I could play with this all night.

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    Quote Originally Posted by D0ming0 View Post
    Don't say I have no life, but...

    Block is 10 cm wide.


    Who needs Call Of Duty, I could play with this all night.
    And all of them are useless because it doesn't help you calculate anything.

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    [edit] im sorry i didnt look and thought the 3d renderings been done by the op.

    Last edited by sone_one; November 20th, 2012 at 05:30 AM.
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    Let's not turn this into a discussion about what is right and wrong in the learning process.

    Thanks to all! Now I have a more clear understanding of the subject.

    Have a good day!

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    [edit] im sorry i didnt look and thought the 3d renderings been done by the op.

    Last edited by sone_one; November 20th, 2012 at 05:30 AM.
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    After looking at D0ming0's 3D render, I thought of something : in situations where we don't have money to pay for models to pose for us etc., it's not a bad idea to use Poser / DAZ Studio to help us calculate the lighting and where the shadows should go etc? I don't mean to use the models for anatomy reference, but more for lighting.

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    No Xeon - Poser and DAZ won't do you any good because if you understand enough about the figure, you understand enough about the light. You're better off just working with traditional methods and direct observation than trying to fake it in some ill-conceived software. If you want to do it right, look to Gurney, and the countless other artists working in that same approach. Just mho.

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    The only thing I'd use those programs for is getting a rough idea of a pose in an odd perspective your likely not going to see in real life. But you still need knowledge in general to put any of that to use.

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    Quote Originally Posted by dpaint View Post
    And all of them are useless because it doesn't help you calculate anything.
    Wow. Way to be an ass to someone's who put effort into trying to help.

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    I dunno, Poussin used to construct whole scenes with little wax figures for lighting reference, I don't see how using a 3D program to do the same thing is much different... And 3D programs can be handy for getting rough perspective guidelines on complex objects from multiple views in a hurry (say if you're drawing a comic featuring an elaborate spaceship in hundreds of panels, or something...)

    People didn't used to use digital tools to concoct reference because the tools didn't used to exist. Now that they do, why not use them, if you find them useful for a given situation? Of course, as with ALL reference, you have to know how to adapt and edit anything you use as ref, otherwise the results look like cheap 3D, or wax manikins, or bad snapshots, or pterodactyls made of cardboard, or your cousin Joe in a fright wig, etc...

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    Quote Originally Posted by QueenGwenevere View Post
    I dunno, Poussin used to construct whole scenes with little wax figures for lighting reference, I don't see how using a 3D program to do the same thing is much different...
    I would say that really depends on the quality of the program in question (and skills of the artist), seeing how how naturally they actually work with light and shadow (like with reflected light for example) can vary wildly, meaning that at worst the 3D mock lighting will look really fake or plain wrong.
    And then there's the quality of the actual light to consider too, not sure how well 3D programs even today adapt to that...

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    That's why I say you need to know how to adapt your reference, whatever it is.

    Crude 3D is just as crude (or likewise just as useful) as crude paper mâché and clay, but both are totally valid tools IF you know how to use them intelligently.

    I'm just a bit tired of the knee-jerk reaction against using any digital reference at all just because it's digital. That's no reason to reject it out of hand. As with any ref, it all depends on how you use it, and who is using it, and what for.

    Using Poser to study anatomy? Bad idea. Using Poser to get a general idea of the cast shadow of a figure in a complicated pose seen from twenty feet overhead...? I can see that being useful.

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    Quote Originally Posted by dpaint View Post
    And all of them are useless because it doesn't help you calculate anything.
    Wow, strong. Did you get beat up by a 3d app or something? Next time I'll get my son's blocks and a torch out. Equally useless but maybe less offensive to some. Or maybe I should have got the oils and canvas out?

    And I disagree, you can clearly see how the shadow is affected by the relationship between the width of the object to the width of the light source. While not definitive by any means, it is at least an indication of what (generally) going on.

    And I note from your stab at helping...oh wait, you didn't bother....

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    Get a fucking 2x4 block...and a light.

    And I disagree Queenie...by the time someone has monkeyed around with Poser to see complicated shadows, from questionable lighting algorithms, from 20 feet above the character...you could have set that up with any mannequin, lit it and observed for yourself what is happening.

    3D certainly has uses...no one is discounting them outright simply because it's digital. But it's just ridiculous to use in most situations. Unfortunately many people who lack observational experience are unaware of the difference.

    Again, if you want to figure this stuff out then stop reinventing the wheel. Study perspective theory if you want to understand shadow projection. Set things up in the real world to observe.

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    Quote Originally Posted by D0ming0 View Post
    Wow, strong. Did you get beat up by a 3d app or something? Next time I'll get my son's blocks and a torch out. Equally useless but maybe less offensive to some. Or maybe I should have got the oils and canvas out?

    And I disagree, you can clearly see how the shadow is affected by the relationship between the width of the object to the width of the light source. While not definitive by any means, it is at least an indication of what (generally) going on.

    And I note from your stab at helping...oh wait, you didn't bother....
    No, unlike you I actually work as a 3d artist when I want to. Your post was as useless as your taunt. He asked how to measure where the shadow would go obviously anything hard like simple math isn't your strong point. Jeff answered the question, its covered under point light perspective theory. Look it up, if you can read beyond third grade comprehension.

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    Quote Originally Posted by dpaint View Post
    No, unlike you I actually work as a 3d artist when I want to. Your post was as useless as your taunt. He asked how to measure where the shadow would go obviously anything hard like simple math isn't your strong point. Jeff answered the question, its covered under point light perspective theory. Look it up, if you can read beyond third grade comprehension.
    I am aware of what Jeff said, and I agree that he is stop on. However, I was simply illustrating a few examples of how his setup might look. I was giving an indication in a friendly way in a (what used to be) a nice cooperative forum where everyone could join in.

    Sorry, I wasn't aware that this was now your forum, and all discussion is to be stamped out once the question has been answered to your satisfaction.

    Anyway, I'm going to leave this now. I love this place, and hang out here daily, even if I don't post often. It makes me very sad to think how this looks to anyone who has the misfortune to come across it. This shit is upsetting enough when I see it happen to others, but now I know how it feels.

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    Quote Originally Posted by dpaint View Post
    No, unlike you I actually work as a 3d artist when I want to. Your post was as useless as your taunt. He asked how to measure where the shadow would go obviously anything hard like simple math isn't your strong point. Jeff answered the question, its covered under point light perspective theory. Look it up, if you can read beyond third grade comprehension.
    Lmao

    Let all that anger out. Hahaha

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    3d apps (pretty much all of them) are capable of reproducing, or rather faking, real light conditions. but not by the click of a button. takes alot of knowledge to adjust those render settings, and even more building a light-rig, there are actually professionals doing mainly that.

    i agree that the renderings here show a few aspects of cast shadows, but in the end its just a diagram without an explanation how to get there without a 3d app.

    the right answer is tinybirds and jeffs suggestion... basics of perspective... it tells us that the castshadow in this case, is potentially infinite, but after a certain point, depending on falloff and strength of your lightsource (on an infinite flat plane), it just merges with the sourroundings due to general absence of light. so practically its as long as the surface its cast on is illuminated (by that lightsource!).

    Last edited by sone_one; November 20th, 2012 at 05:50 PM.
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    I certainly have no problem with resolving, or verifying, hard shadow or any other planar perspective projection geometry issue using a 3d app, they work perfectly for that.

    Last edited by bill618; November 20th, 2012 at 07:14 PM.
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    3d has it's flaws. However there are people who developed great sense of how light works from doing stuff in 3d software and then they incorporated it in their artwork when learning to paint. Mathias Verhasselt who posted on this forum long time ago is good example of such person. Other example would be Maciej Kuciara, I think.

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    Quote Originally Posted by sone_one View Post
    i agree that the renderings here show a few aspects of cast shadows, but in the end its just a diagram without an explanation how to get there without a 3d app.

    the right answer is tinybirds and jeffs suggestion... basics of perspective... it tells us that the castshadow in this case, is potentially infinite, but after a certain point, depending on falloff and strength of your lightsource (on an infinite flat plane), it just merges with the sourroundings due to general absence of light. so practically its as long as the surface its cast on is illuminated (by that lightsource!).
    Yep, it's beyond me to explain it well, hence the renders. Although I like your explanation above. I should copy that into my post :-)

    The point I found interesting is the difference effects you get from using an area light source of varying size (like I posted). Those were produced using Cinema 4D's physical renderer, which should be accurate enough (within the bounds of the basic setup I used). My aim was to illustrate some simple, easy to visualise examples.

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    Like I said, it depends who you are, what you're doing, and why. If you already have 3D software and are adept with it, you might find it a lot faster to throw some things together in 3D than to try and fake them physically. Especially if you have limited tools and space and are totally hamfisted when it comes to making things out of wood or clay or what-have-you.

    I mean, Maxfield Parrish might build whole tiny castles out of wood, but he had a woodshop and woodworking skills. If it was me, it would take me way longer to try building a miniature wooden castle than to try making a virtual one, plus I'd have to go buy a lot of woodworking tools and rent another space. Heck, forget woodworking, I'd probably take all day trying to build a miniature castle with sculpey and toothpicks... But that's just me. I'm terrible at actually building things. I'm better at wrangling code.

    3D is obviously not for everybody, and just like photo ref or manikins it won't work well if you have limited experience - SAME AS ANY REF THAT ISN'T THE EXACT THING - but it is going to be more convenient for some people in some situations. Heck, my Dad does most of his ID sketching straight in 3D these days, and for him it's way faster and more convenient than working on paper.

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    Quote Originally Posted by D0ming0 View Post
    The point I found interesting is the difference effects you get from using an area light source of varying size (like I posted).
    just basic perspective and figuring out where the lightrays are blocked, where not and how far the reach.

    if you want to get the rough idea of a castshadow i too, see nothing wrong in using a 3d app. if you want to study light, get a block, ball, glass, whatever and hit it with a lamp. this will provide you with real information, youd need to spend hours on recreating in 3d. and heres the funny thing... if you dont know that stuff (as in havent studied it from life) you cant get your 3d app to get there, because its not doing it on its own.

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    Quote Originally Posted by HunterKiller_ View Post
    Wow. Way to be an ass to someone's who put effort into trying to help.
    I gather that technically he's trying to sound like a "badass", but that may be just a particular kind of ass.

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    Quote Originally Posted by briggsy@ashtons View Post
    I gather that technically he's trying to sound like a "badass", but that may be just a particular kind of ass.
    Always makes me smile when you comment about anything art related. Do any painting lately David?

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