Render problem, grey artifacts

[stig_olsen]

Hi,

 

Im having problems rendering, as I get some grey artifacts in the darker areas of my cubes.

I have attached the project file, but also some stills that I hope some of you can take a look at. They describe the problem very well.

The different stills also show some of my settings.

 

Thank you.

 

Stig

artifacts.hipnc

[bandini]

Looks like a shading error related to interpolated normals of your geometry.  You have kind of a rounded cube look appearance.  You may want to append a vertex sop with "cusp normals" set to a certain angle, or a facet sop set to cusp normals.

[stig_olsen]

Thank you bandini!

 

I did apply te vertex sop, set it to "cusp normals", and it did straighten up the lines. But, it didnt help me out with my problem.

If you have time, I would really appreciate if you took a look at my project file. I really think this is a beginner issue, that you you will find as soon as you see my setup.

 

Thanks again!!

 

Stig

[stig_olsen]

Hi again,

 

As you can see on the attachment; this is what happens with only the environment enabled and a vertex sop after the box sop with cusp normals set to 20.

 

Stig

[Guest tar]

try turning off reflection in the shader

[stig_olsen]

Now I disabled "reflect light" in the shader, and it looks like in the attachment.

I still feel it looks "wrong" in a way. Do you agree?

 

Stig

[Guest tar]

Try to setup a new scene with one cube and do look development on it. Once you get the look you are after transfer it into the scene.

[anim]

in scene, where you've added vertex SOP, select xform2 beneath it and uncheck Recompute Point Normals as that is destroying your vertex normals you've just computed

or add that Vertex SOP below it or after the copy, etc

 

in your original scene you can select box1and uncheck Consolidate Corner Points, it's less efficient than having vertex normals since it's actually splitting the geometry, but it's an option

 

then the other problem you may have is low attenuation on SSS component which can cause dark areas in the corners, you may want to increase the attenuation, also add some multiple scattering may soften it 

 

reflection is fine

[stig_olsen]

Thank you Anim, that feedback totally did it!

I still have some "bad resolution" in the darkest areas but I guess that can be sorted out.

 

Hope you dont mind if I ask you some basic questions...:

- Why do I need to add this vertex SOP with the Cusp normals, are these normals a reference for the material to be applied correctly?

- Why i these normals so important for such an easy thing, and does the same apply to other geometry as well, for instance for adding material to a sphere or a tube?

 

Stig

[Guest tar]

Not sure why you don't test with one cube... basic questions need simple tests.

 

Do you know what normals actually are and do?  Do you know how to look at them in the viewport?  Once you research this, all questions are answered.

[anim]

polygonal models are composed of limited amount of flat polygons which in render would be visible the same way as when you turn on Flat Shaded mode in viewport

that's why each CG app has the ability to specify N attribute which can be interpolated over the polygons which in render will give the impression of smoother surface Smooth Shaded Mode

because this interpolation is happening by default over all connected geometry you have 2 options to create hard edge/flat polygon shading (that's what you were after with cube)

 

1. splitting polygon mesh at the edges you want sharp, (hence the option of not consolidating corner points in Box SOP)

for that you can use Facet SOP, (Unique Points or Cusp Polygons mode)

or Edge Cusp SOP or Vertex Spilt SOP, ...

 

OR

 

2. creating vertex normal, since usually every Point has as many Vertices as Faces it belongs to, specifying vertex normals allows you to specify different normal for each face corner belonging to point therefore create hard edge, or flat face if you set the normals  of all vertices of the polygon to be parallel to polygon normal itself, or in other words to be perpendicular to the polygon plane itself

for this you can use Vertex SOP (Cusp Normal)

or any option of 1. for splitting the mesh then Attrib Copy SOP to copy the vertex N to original unsplit geometry

Edited July 25, 2014 by anim

[stig_olsen]

Thank you, that cleared up a lot!

 

I guess you mean that the objects in smooth shaded mode (not flat shaded) in viewport will be visible the same way in render?

When viewing the box without the cusp normals the box looks exacly the same in viewport as in render. The light fall incorrectly on the faces.

When cusping the normals on the box, the light fall correctly on the faces and in render.

 

Why is flat shaded mode an alternative to use, when its not a correct representation of how the render will look like?

 

Stig

[bandini]

 

Why is flat shaded mode an alternative to use, when its not a correct representation of how the render will look like?

 

 

Just represents display settings, such as wireframe, headlight lighting, etc. Can be useful to look at faceted geometry so you can understand the polygon flow without calculating interpolated normals or wireframe overlays. Anything you draw in the viewport and all those extras like interpolated normals, ambient occlusion, lighting, shadows, etc. takes time and gpu processing power. It's just one form of a display representation.  If you want something more accurate to what your render will look like, use smooth shading view.

[Guest tar]

Thank you, that cleared up a lot!

 

 

 

 

Lol - your questions showed nothing was cleared up.  Once again, the 3d fundamentals are required.

 

[stig_olsen]

Thanks everyone for answering my questions!

 

Marty,

As you understand I have no modeling experience, but Ive used normals to other tasks, like directing velocity on particle streams and making object paths.
Since I didn’t know that the normals also affected how the faces read the light, Bandinis explanation was very helpful to me, and "cleared up a lot".
The link between the viewport and render was also a direct and helpful answer to my next question.

 

Stig

[Guest tar]

Ok I guess learning the axioms is usually the normal way. Top down learning obviously leaves large gaps!

[stig_olsen]

Word!