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I am having a conversation with a co-worker about the properties of light on cylinders. Can someone please help clear this up? I have posted an image that I whipped up in Xara X to illustrate the two views. I know that the tops of the cylinders are not shaded correctly...I'm more interested in the sides.
The question is. If light is hitting a cylinder at a 45 degree angle, will the cylinder be evenly shaded top to bottom like the cylinder on the left or will it have a diagonal shade like the cylinder on the right??
Thanks,
Robert
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I am having a conversation with a co-worker about the properties of light on cylinders. Can someone please help clear this up? I have posted an image that I whipped up in Xara X to illustrate the two views. I know that the tops of the cylinders are not shaded correctly...I'm more interested in the sides.
The question is. If light is hitting a cylinder at a 45 degree angle, will the cylinder be evenly shaded top to bottom like the cylinder on the left or will it have a diagonal shade like the cylinder on the right??
Thanks,
Robert
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I just wondered how you could ever consider anything different...
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If the light covers the entir length/width of the shape, then the fall off will be a verticle blend(ex. #2 below).
If it's a smaller source like a flashlight, for example, that doesn't cover the entire shape it wouldn't be either of yours. The fall-off of the light to shadow will be an elliptical blennd (ex. #1 below)
Hope this makes sense!
Steve Newport
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Steve
Your illustration is very good. To add a bit more realism, I like to had the far side a bit lighter to represent reflected light. The darkest part of a cylinder is usually next to the highlight as you have illustrated it.
Gary
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<BLOCKQUOTE><font size="-1">quote:</font><HR>Originally posted by Steve Newport:
It depends <HR></BLOCKQUOTE>
Wfcentral's question was, I quote:
"If light is hitting a cylinder at a 45 degree angle"
Maybe you should try to read next time.
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Best to keep quiet and have people think you rude, than to open your mouth (virtually of course) and prove it! [img]/infopop/emoticons/icon_razz.gif[/img]
Whereas the first example may be theroetically correct, Steve's second image, in my opinion, looks more natural and is more believable. If you know anything about art history, you know that historically artists have taken the path of what looks natural and believable as opposed to the anatomically correct path.
Gary
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Maybe just...
Peter Pan sees a closed the closed (not hollow) tube.
Steve sees tube which is opened at the top.
Then, of course, if we think about closed top of the tube, Peter is right while Steve is right when we regard the top of the tube as opened and tube is considered being hollow. (uh.. I speak somehow weird today ;-))
Roman
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Mr. P, nice to see you back again, hope you had a Merry Christmas or chanuka or Kwanza, whatever you celebrate. BTW, Steve is fine for the salutations.
Just one little thing before I start my explenation, you quoted me saying...
[QUOTE]Originally posted by Peter P.:
Quote: "Originally posted by Steve Newport:
It depends "
QUOTE]
I only said "Depends", how bout you start reading!
Anyway, my explenation is quite correct. In both of my illustrations the light is coming from a 45 degree angle, Just in one case, the 45 degree angle light is not completely covering the cylinder. I made a picture for you just in case you're mind can't comprehend these words (See below)
Here, try it yourself. Hold a flashlight at a
45 degree angle over a cylinder (A cup or a mug, be creative) in a dark room so that the the edge of the light is at the center (Highth-wise) of the cylinder. You will see that the fall-off is, in fact, elliptical!
I hope you understand now!
Think before you speak Petie, you might not be held as such a moron then!
Roman, I'm not really seeing what you're saying!? Maybe I'm just stupid, I dunno!
And Gary, I have quite the same outlook as you. In art, what looks right is better than what is correct. Thanks
Steve Newport
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So can't test your example Steve. However it sounds like Robert's original question can't be answered without knowing the light elevation... there is always one more detail [img]/infopop/emoticons/icon_eek.gif[/img]
Roman, does the shadow on the back of the object really change depending on whether the object is hollow or not? I quess I see (if hollow) how a reflection could change the light in front (bouncing back from the inside??), but would it effect the back?
I'm going to have to find a dark room, batteries and a cylinder somewhere [img]/infopop/emoticons/icon_biggrin.gif[/img] [img]/infopop/emoticons/icon_biggrin.gif[/img]
Mickie
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that people who post the most inflamatory messages never have an e-mail address in their profiles? [img]/infopop/emoticons/icon_eek.gif[/img]
Gary
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somehow like this.. (lousy example follows)
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Is GOOD BASIC STUFF. It should help a lot of us "learning" or "less knowledgeable" want-to-be artists.
I would like to see MORE EXAMPLS of "lighting" tricks. Ie; for different object shapes and different colored lights in different type of environments. And like Steve and Gary have tried to point out; what is real in nature may not be visually as effective in an artistic rendering ... that's where different techniques (tricks) come into play.
Info of this type can go LONG WAY in a forum of this nature.
Thanks, Robert for asking, and thanks Roman, Steve, and Gary for the lesson and examples.
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A good discussion of lighting theory here. From my days as an instructor of television production -- the closer the light is to the subject, the greater the intensity of the light measured at the subject.
There are a lot of variables at play. If the light is aimed at the top of the cylinder and is coming from a 45-degree angle, you should get a brighter reflection from the top of the cylinder than from the bottom. Whether you could see this, however, depends on the brightness (intensity) of the light source, the size of the cylinder and the distance between the light and the cylinder.
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Although not expressed in my examples, your comment is 100% correct Bob and could be very usefull to everyone in here, especially Petey over there! Thanks for the tip!
Steve Newport
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Boy, what a response we got on this thread. Sorry to see so many people get up in arms. Anyway, I thought you might like to see the type images we're creating in my office and why we were debating lighting. We are not concerned with the amount of light - we assume a daylight setting. We are more interested in the 3D look than whether it is clinically correct. I just need to illustrate to students so that they can tell whether a part is a cylinder or a flat piece of metal. The image below is part of a larger piece that goes into flash and becomes animated.
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If it's sunlight, then it would be your first example, even if it's not it looks good that way, so I think you're set! I'm assuming you're talking about the cylinder attached to the center of the wheel? Thanks for the Question!
Steve Newport
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Robert, here are some croppings of some illustrations I did for a browser-based operations manual.
These were done with CorelXara (before the advent of the timesaving eyedropper and shadow tools). OBVIOUSLY, my lighting techiniques violate the laws of nature. But I found that, due to the restrictions of size and the "zoom level/camera distance", realistic lighting could not accentuate certain components when viewed via a browser.
I guess you could say what I have done here is not really a "lighting" technique but rather a "contrasting" technique.
Regards
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John, those images are striking and very effective.
I think there is a lesson to be learnt here - it's not what looks most realisitc, it's what looks most effective. Johns images are a long way from looking realistic on a purely scientific level, yet somehow they achieve a 'realism' that's much more effective.
The choice of colours potrays the image in a much better way, making it easier to understand.
Michael Ward
http://www.metalandplastics.co.uk
http://www.leighcenturions.net
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Michael, thankyou for your kind remarks. I'm surprised at times what Xara can enable someone to produce. Although the process of doing something like these postings can be quite tedious [img]/infopop/emoticons/icon_smile.gif[/img]
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Klaus - it looks great!
Regards, Ross
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