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Thread: Question about edges are they darker?

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    Question about edges are they darker?

    Hi, I get:

    1. Planes appear lighter or darker depending on the angle they are compared to the light source

    2. Planes can appear lighter or darker depending on position of the observer. ie. because not all light is reflected in random directions, smooth objects can reflect more light at a certain angle.

    But

    I want to know if a plane appears darker because it is oblique to the observer. This is suggested here: http://conceptart.org/forums/showthread.php?t=14739

    on page 2

    If so, why?

    Does that explain why the horizon is darker (ie. planes further away will get closer and closer to being oblique) or is it just the waves bunched up. see here:

    http://stapletonkearns.blogspot.com/...rtance-to.html
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    Two things are happening , something one of my instructors called Spontaneous Contrast which is essentially an illusion. You may also be observing that the part that is darkest is almost paralell to the rays of light, so it's catching less light, (less reflected light and direct light)
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    Quote Originally Posted by sharprm View Post
    Hi, I get:

    1. Planes appear lighter or darker depending on the angle they are compared to the light source

    Does that explain why the horizon is darker (ie. planes further away will get closer and closer to being oblique) or is it just the waves bunched up. see here:
    It has more to do with #1 - the orientation of the plane to the light.

    The horizon isn't generally darker - rather lighter in "most" situations, due to atmospheric perspective and it being flat to the light source (sun or sky).

    The important thing to keep in mind is there aren't any rules to these things - at least not when it comes to the landscape - still life is a little more controlled and therefor subject to more consistent "rules".

    If you want to further understand the idea of planes in the landscape get a copy of "Carlson's Guide to Landscape Painting" - which is what Stapleton is referencing in his article.

    Hope that helps!
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    >"Spontaneous Contrast which is essentially an illusion" - can you explain more? Does the brain see things differently than they should appear. Where a light object overlaps a dark object, does the brain put a darker edge on the dark object?

    Jeffxx9:

    But if you look at the horizon it is darker in that situation. Why? Is it specific to those waves (ie. the light side of the waves are hidden by the dark side - deeper ocean etc.) or is it an illustration of the plane "oblique to the eye".

    What I'm asking is if I had a plane in 3ds max and I had a light source that was directly above it and both had the same axis of rotation, so when I rotated the plane the light was still directly above it, and if I rotated the plane so it became "oblique to the eye" would it be dark?

    Thx for help srry I posted in wrong section
    Last edited by sharprm; April 1st, 2010 at 04:55 AM.
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    I will explain it for you since some of the responses are lacking in explanation.

    In the standard fixed function graphics pipeline, light is modelled as several terms.

    Ambient, Diffuse, and Specular.

    Ambient light is essentially blanket light coverage that illuminates all objects. It is light that has bounced around so many surfaces that it is impossible to detect the source. Ambient lighting is generally very smooth and uniform across the surface of an object.

    The next term, diffuse, is light that reflects from a source in a spread out way. This is generally attributed to the uneven surface of an object so parallel rays of light bounce off the object 'diffusely'. This is your general lighting term.

    The last term, specular, is light that reflects at a specific angle. This is generally attributed to shiny, smooth surfaces. Light no longer reflects as a spread, but reflects as a point. Specular light can only be observed at certain angles.

    These are the three basic terms and applies for both light coming from point sources and for light reflecting off another surface.

    The whole 'darker as the plane turns away from you' is a simple artistic tool to emphasise the mass and form of a shape. In the real world, we need no visual cues to perceive depth. We have two eyes and depth is created as a combination of two images taken at two different angles. When we deal with a 2D image, we need a little extra help in order to perceive it as a three dimensional object. Thus artists tend to make planes facing away from the viewer darker than those facing the viewer. It is nothing more than artistic representation and isn't really present in the real world.

    Vilppu explains is better than I can so if you want more info (or a better explanation) go to this link: http://www.awn.com/articles/tutorials/using-tone-draw
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    Thanks alot M-Kaibigan! I appreciate the clear answer. I'm nolonger confused, the "oblique to the eye" was a representation method. The links seem good but I haven't read it properly yet.

    One last question: light falls off at 1/r^2. Reflected light seems stronger the closer the plane is to the reflecting plane. When you are drawing from imagination, are there some rules for how bright the reflected light will be based on distance?,

    If not its okay I'll just copy some busts/statues. Thanks for your help guys.
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    Quote Originally Posted by sharprm View Post
    Hi, I get:

    1. Planes appear lighter or darker depending on the angle they are compared to the light source

    2. Planes can appear lighter or darker depending on position of the observer. ie. because not all light is reflected in random directions, smooth objects can reflect more light at a certain angle.

    But

    I want to know if a plane appears darker because it is oblique to the observer. This is suggested here: http://conceptart.org/forums/showthread.php?t=14739

    on page 2

    If so, why?
    Not sure what you are referring to here, edges or planes? It does talk about contrast and keeping local value accurate. Where did your observation come from, the picture or description?

    From the picture I can only see the cores that could look like what you are describing. Cores are darker for effect because of contrast and it's true in most cases where the reflect light would be the least in the core area. This somehow generalised into a method in art and is used to punch the effect.



    Does that explain why the horizon is darker (ie. planes further away will get closer and closer to being oblique) or is it just the waves bunched up. see here:

    http://stapletonkearns.blogspot.com/...rtance-to.html
    Water have some additional qualities to take into account.
    Question about edges are they darker?

    The texture of the water is waved, the further back into the distance you go the more of the water reflective qualities get blocked by waves due to the perspective and thus you see more darker non reflecting wave bodies. Yes, you can say then it's because they are bunched up.
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    Not sure what you are referring to here, edges or planes? It does talk about contrast and keeping local value accurate. Where did your observation come from, the picture or description?
    Hi it just came from the picture 'Materials property page 2'. He shows a dark part where "rolls away from light source". He creates a second dark part (which is not away from the light source) and says it "roll moves oblique to the eye". I thought that they are two seperate things. I thought it was just the edge (but an edge is a small plane almost parallel to the line of sight of viewer). Do you think "roll moves oblique to the eye" refers to the edge or the planes well inside?

    M-Kaibigan seems to have explained it though. "roll moves oblique to the eye" has no justification. It is there just to aid the viewer.

    My observation about the horizon was just a one off I saw (that's why I was excited and posted about it). Because if you draw a line from a point on a plane to the observer it will form an angle theta. But the further you make that point away then the smaller theta will be. Hence it is like "roll moves oblique to the eye". This could explain it getting darker. But as you say the correct explanation is that it is the waves bunching up because "roll moves oblique to eye" is not real, just to aid the viewer.

    Maybe we would see it in photos with the flash on though.

    Not sure what cores are.

    edit:
    The next term, diffuse, is light that reflects from a source in a spread out way. This is generally attributed to the uneven surface of an object so parallel rays of light bounce off the object 'diffusely'.
    does diffuse light reflected at all angles evenly? ie. if I did that plane with the light source directly above and both are rotated, would the brightness change, or would that only happen for specular?
    Last edited by sharprm; April 1st, 2010 at 08:12 AM.
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    The appearance of diffuse light depends greatly on the material.

    Question about edges are they darker?
    Image from wikipedia.

    It's essentially light that has low contrast and no hotspots. Again, depending on the surface, it generally doesn't change drastically based on your viewing angle. Since there are many many micro-facets, all presumed to be facing random directions, for a given area it will generally distribute light equally in all directions.

    In the case of a rotating plane lit directly above, I would say (for most materials) the diffuse term would constant. The specular term would be changing however. This would essentially be 'flat lighting' and one would generally try to avoid these cases as it doesn't really describe the direction of the forms best.

    I would draw up some images of my own to show/explain it better but I don't have my tablet with me 'n'
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    Quote Originally Posted by sharprm View Post
    My observation about the horizon was just a one off I saw (that's why I was excited and posted about it). Because if you draw a line from a point on a plane to the observer it will form an angle theta. But the further you make that point away then the smaller theta will be. Hence it is like "roll moves oblique to the eye". This could explain it getting darker. But as you say the correct explanation is that it is the waves bunching up because "roll moves oblique to eye" is not real, just to aid the viewer.

    Maybe we would see it in photos with the flash on though.

    Not sure what cores are.
    I see. Cores are the rim of the edge of a plane where the shadow starts, if you have seen loomis illustration on a ball, the rim is made darker and is called the core.

    The waves effect is simmilar to other effects, like skin. Look at the top of your hand , the planes that are oblique to the eye are more brown/tan color and the planes facing the eye is more pink/fleshy. If you look at your skin texture under a magnifying glass you will see the same effect as with waves. Your hand is covered with little wave or scale like bumps. Since at the oblique angle you see less of what's going on underneath the surface skin you see more of what's on the little skin shell. The bumps are more dead skin and tanned skin where as the skin in the crevice's are more pinkish and even red file folds or white.

    So, depending on the material quality you would have the same, but you can't really say it will go darker, it might but it depends on what you see at the particular angle microscopically.

    edit: does diffuse light reflected at all angles evenly? ie. if I did that plane with the light source directly above and both are rotated, would the brightness change, or would that only happen for specular?
    Diffuse is the smallest/finest texture effect and it' bouces in theory evenly in all directions. like matt is just like looking at sand paper but since the ocean have a more arraged texture behaviour it will have some angles that behaves uniquely almost like some other materials like silk, CD's etc..

    The ocean go darker at those areas because the depths looking into the ocean is darker there. If there where a alien luminosity that would have made the ocean brighter under the water than the sky then the ocean would have become brighter into the distance and less "sky blue"

    Secular light is noting other than reflection. So if you move the secular would move. In reality there is no pure diffuse so there is some micro scattered seculars in there changing the saturation of the surface and even changing the hue depending on the color of the light source.
    Last edited by George Abraham; April 1st, 2010 at 10:38 AM.
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    To the ambient, diffuse, and specular lighting you can add a zoo of other things.

    Reflectivity and Fresnel index: some things are reflective, some are matte, some (like water) are more or less reflective depending on the angle you view them at. Water in the distance is highly reflective, water right at your feet is barely so.

    In fact, there is really no diffusion and specularity. Specularity you get when the surface is reflective enough to give you an image of the light source. "Diffuse" lighting is either due to surface texture that breaks the reflection down, or found in the lit areas beyond the light source reflection.

    Anisotropy: things with fine-grained directional texture have shaped reflections that stretch across the texture. Applies to lots of things, from hair and vinyl records to brushed metal and waves in the distance.

    Translucence, also known as "subsurface scattering": diffusion of light through the object, rather than off its surface. Many organic things like wax, horn, organic tissue show this property.

    The one most relevant to the question about darkening of edges is the ambient lighting occlusion.

    Since the ambient lighting depends not only on the light scattered in the atmosphere, but also on the light scattered off nearby objects. (Including other surfaces of the same object, of course, if they are in the right position.) If something is close enough to your object that less scattered light enters into the space between them, both surfaces will darken.

    This is the reason why there are darker edges between fingers, in the nostrils, between touching body parts.
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    Quote Originally Posted by sharprm View Post
    >Does the brain see things differently than they should appear. Where a light object overlaps a dark object, does the brain put a darker edge on the dark object?

    Jeffxx9:

    But if you look at the horizon it is darker in that situation. Why? Is it specific to those waves (ie. the light side of the waves are hidden by the dark side - deeper ocean etc.) or is it an illustration of the plane "oblique to the eye".

    What I'm asking is if I had a plane in 3ds max and I had a light source that was directly above it and both had the same axis of rotation, so when I rotated the plane the light was still directly above it, and if I rotated the plane so it became "oblique to the eye" would it be dark?
    Lots of good technical information here. So I see, you're talking about modeling - when working from imagination or setting up environments I try to err on the side of general observation "rules" based on the lighting conditions and subject of the scene. Carlson's landscape "planes" theory is great for this - but drapery, the figure, still life are not subject to atmospheric perspective the way thte landscape is.

    So yes, the brain does see things differently because it sees things relative and it edits a great deal of information. A camera sees things much differently as well and is part of the problem with the seascape - the camera cannot accurately record relative values the way your eye/brain does. But yes, I think in that example it is specific to the wave pattern and lighting condition. The ocean, even more than the landscape, often is so light at the horizon that it is lost into the sky or atmosphere.

    Like I mentioned earlier, you can't go from one photo and draw conclusions about all the various factors in the environment/landscape - they change every minute of every day anyway and a camera doesn't even come close to capturing anything but form/detail. You're best bet is to stick with generalized "theory/rules" that work for the situation you are modeling/simulating.
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    Quote Originally Posted by zaorr View Post
    I see. Cores are the rim of the edge of a plane where the shadow starts, if you have seen loomis illustration on a ball, the rim is made darker and is called the core.

    From the picture I can only see the cores that could look like what you are describing. Cores are darker for effect because of contrast and it's true in most cases where the reflect light would be the least in the core area. This somehow generalised into a method in art and is used to punch the effect.
    I just wanted to check I got this point. So the core is there because it is further/facing away from the reflected light? (see diagram) But it could be done even in situations where that wasn't true just for effect.
    Quote Originally Posted by zaorr View Post
    The waves effect is simmilar to other effects, like skin. Look at the top of your hand , the planes that are oblique to the eye are more brown/tan color and the planes facing the eye is more pink/fleshy. If you look at your skin texture under a magnifying glass you will see the same effect as with waves. Your hand is covered with little wave or scale like bumps. Since at the oblique angle you see less of what's going on underneath the surface skin you see more of what's on the little skin shell. The bumps are more dead skin and tanned skin where as the skin in the crevice's are more pinkish and even red file folds or white.
    Thanks! I was wondering about that.

    JeffX99: The book is on google books so I will check it out. I'm not into landscapes at the moment though I just read stapleton's blog because it has so much good info on drawing.

    arenhaus: I might stick to simpler stuff for now though if you have a good link that explains how to use that info in drawings please share. Thanks.

    edit: just to explain the diagram, it is supposed to see how the core could come about. I labelled the whole thing 'potentially incorrect' (not saying loomis part is incorrect, just my explanation of it). I think if there were ambient light but no reflected light there should be no core. It is only when there is reflected light that there is a core.
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