Weird Black "Shadows" On Rendered Image

Question

I'm getting these weird black shadows on my rendered image of this mailbox I'm making. Here's a link to the file and a link to YouTube so you can see what's going on.

I was able to mess with the normals and removed all doubles and this is what I was able to come up with. That will still not go away unless I change the texture to diffuse, and it's not a shadow: I've moved my lights and camera trying to see but it wasn't.

EDIT:

So did all that stuff and still no luck, It did make it look better but on the angle that I want for the pic there is still an area. I have found that if I rotate the camera there are certain areas where this "shadow" does not occur. I also checked to see if maybe the letters or the top of the mailbox was casting a shadow in some way, but that was not. I also moved my light sources around, took away the floor, and added more objects around to see if it would work. Well it still has that unsightly shadow, although it does look better I'm just surprised there is no way to get rid of that black shadow that I know of.

Here is a pic of my current progress

It's kind of hard to see in that pic but at the bottom right corner there is still a weird shadow. Also I found if I take off the top there is an unsightly shadow on the top of the main mailbox mesh. And this is after I deleted duplicates and checked my normals, etc.

Answer 1

A lot of your normals are facing inwards. You probably can't see this because backface culling is disabled by default. I always keep it activated so I can see these problems right away. Here's what it looks like with Backface Culling enabled.

You can view the normals using the following setting.

You can flip them with the following tool in Edit mode.

I also use remove doubles because there were many vertices that were overlapping which were not attached to each other.

The door is partially attached to the rest of the mail-box at the bottom which makes the polygon flow difficult to work with.

Also, there is a shelf inside the model which is attached to the outer polygons, this may be intentional but has the same effect as interior faces: it causes rendering artifacts and was the biggest problem here.

Cycles cannot handle super low-poly models very well. Basically triangles become very dark and visible at areas where the lights hit them at glancing angles. Adding more geometry, lights and an HDR texture can help with this.

I used inset on the top piece and some loop cuts along the rim.

The main box and the door have a Bevel Modifier attached and set to 'Angle'.

I applied the Solidify modifier on the door latch/hook thing and added inset and loop cuts to it as well as a sub-surface modifier to make the edges more crisp.

Here's the .blend http://www.pasteall.org/blend/34426

Answer 2

That looks like it is because you have a glossy shader on your object. What is happening is there is nothing for the glossy surface to reflect. You are just seeing a reflection of the (almost) black world which is unrealistic, ugly, and boring.

You can fix this by adding an HDR environment texture or placing more objects in your scene, that way there would be something interesting in the reflections, rather than black[ish] bleah.

Environment textures:

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To add an environment texture simply go to the node editor, choose world as the type of shaders to edit at the bottom, and click use nodes. Then add an environment texture texture node, load in a panoramic skydome environment texture, and plug it into the color input of the background shader. I am using Greg Zaal's Golden Gate

Without environment texture:

With environment texture:

As you can see, the detail of the model and my car paint shader is much more pronounced as the reflections are much more interesting and non-uniform.

But, now you can see that since the HDR is now lighting the scene (and the lighting for the scene is not meant to work with HDR lighting) it is a bit washed out. You can fix this by making the HDR only affect the glossiness of things. This is done by mixing a plain black background shader with the textured one based on the is glossy ray output of a light path node.

(click image to view larger)

You can see I also added a few more nodes here, they just give more flexibility. The texture coordinate and mapping nodes allow you to rotate the environment texture by adjusting the Z-rotation spinner. And the math > multiply node could be plugged into the strength of the background shader to get stronger shadows (brighter areas of the HDR will emit more light), I didn't feel that was necessary for this particular scene/texture combo so I didn't plug it in.

So here is the final result, with a few more objects in the scene to further enhance the reflections:

Answer 3

I've had this happen on only one occasion, and it was caused by a blank UV map that shouldn't have been there.

If you're using a Diffuse BSDF, try selecting your object, go to the materials tab, click the button next to where it says Normal, and click Remove in the top right of the menu.

Answer 4

You need to first remove doubles, then make normals consistent (in the edit mode-selecting all vertices). That should help.

Cheers AM