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for some reason i am getting these black patches all around my image. it seems to be most obvious where certain sections overlap slightly, but i have no idea how to fix them (very new to blender o.o) enter image description here

im not sure why this is happening. heres a version where the points im referencing are circled

enter image description here

i don't know what settings you guys need to know so just ask me if you need too. i can tell you this was only renderd 10x but even at 20,000 samples it did not fix anything

keep in mind, i am still a noob at this so any suggestions please word as simplisticly as possible xD thank you!

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Ok so it turns out my mesh had a few problems of its own. the B's center issue in box was caused by overlapping mesh. so i went in and fixed it best i could. as for the other black spots gandalf3 your suggestion semed to help the most, it didn't fix it completely but i did get this text from the basic text object, then added bevel and depth so im not surprised this happened. im rendering at about 10k samples right now and its looking alot better, if anybody has suggestions on how to prevent overlapping mesh when using the text object i would be all ears. –  user2620255 Mar 19 at 11:26
    
This post has some possible solutions for beveled text. –  gandalf3 Mar 19 at 18:44
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3 Answers 3

up vote 4 down vote accepted

This is caused by sharp, low poly geometry with smooth shading (you'll notice that the problem goes away with flat shading). It's true that bounces can also cause dark spots (as mentioned in the other answers), but I think this is the issue in your case.

There a couple things you can try:

  • Adding more geometry (works well for curved objects)

    No subsurf:
    enter image description here Subsurf level 2:
    enter image description here

  • Using an edge split modifier (works better on objects with sharp edges)

    Without edge split:
    enter image description here With edge split:
    enter image description here

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The black spots are due to the depth limits in the transmission rays. You need to increase the Transmissions rays so that light can gr thorough more objects and the Glossy Rays so that you do not get black reflection from other object (letters) in the scene.

Default Render Settings:

enter image description here enter image description here

Increased Depth:

enter image description here enter image description here

NOTE: that the total number of bounces for each ray is set by the Max parameter under bounces. You also need to increase this if you really want to go over the default.

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that didn't seem to work for some reason, it all looks the same, could it possibly just need more samples with that method of fixing? or a higher value for those options? –  user2620255 Mar 19 at 1:47
    
also i am still only rendering in 10 samples just for the preview window but that at least isn't changeing –  user2620255 Mar 19 at 1:48
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Vaders answer is correct; the number of times a specific type of light ray is permitted to bounce before it is terminated is the problem, and is also correct that it is the Glossy and Transmission ray bounces need to be increased.

The reason you saw no improvement when you made the suggested adjustments is that those values are set in two places.

The value you set for each bounce type (outlined in blue) is the limit for the maximum number of times that type of ray can bounce before it is no longer calculated, depending upon your scene however, it may be terminated before reaching that limit. But; those limits are constrained by the Min and Max values (outlined in red). By way of example; in the image below, despite having a setting of 1, 3 Volume bounces will be calculated, and entering a value of 50 for the Transmission bounces, still only 12 bounces would calculated as the Max value will terminate the ray at 12.

Light Path Settings

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