Rendering Problem - Polyloop

steve_j · 15th February 2006, 00:24

I'm a new user of Carrara 5 and am having a problem rendering with global illumination. I have imported a model (from truespace-in obj format) containing 2 microwave 'horns'. I "creased edges" on the upper horn to make its surfaces look flat. I wanted global illumination so I loaded a background image (snowfield -- supplied with C5) and set the default light to zero. When I render the image using GI, (sky light checked) I get the first attached image -- with the strange smudges on the top horn. The smudges are not there when I use individual lights and no global illumination, but they are there no matter what quality I set for lighting or how many photons I use in GI.

The texture for that horn has Transparency set at 0-100% with the value at 0% (this is how it imported). When I set Transparency to 'None" the smudges go away (the second image). 0% should be equivalent to 'none', don't you think? Also, the smudges only occur in parts of the model that have had edges creased.

It would be an easy workaround to change Transparency to 'none' if the model was as simple as the images shown but there are many other parts and they all have this problem. This looks like a rendering or transparency bug to me -- has anyone seen this before?

bwtr · 15th February 2006, 01:28

Others will reply with proper info but it appers from earlier threads that the setting "None" or "Value 0%" are quite different on all items in the shader menu.

Patrick210 · 15th February 2006, 06:05

Try turning off interpolation in GI.

steve_j · 15th February 2006, 07:02

That did it! Thanks, Patrick. I still think it's a bug, but that is the least objectionable workaround.

andywright · 15th February 2006, 17:01

sounds like you should report it in the bugs section

Patrick210 · 15th February 2006, 17:07

It's not a really a bug. Interpolation is really a down and dirty, quick sampling of the way the photons are working. It can be useful in some situations and it has worked exactly like this since GI came out in Carrara 3. Most everyone is aware of this except persons new to the program who we are happy to enlighten.

andywright · 15th February 2006, 17:51

Quote:

Originally Posted by Patrick210

It's not a really a bug. Interpolation is really a down and dirty, quick sampling of the way the photons are working. It can be useful in some situations and it has worked exactly like this since GI came out in Carrara 3. Most everyone is aware of this except persons new to the program who we are happy to enlighten.

Thanks ... I am enlightened ....I think

I was aware that some of the rendering in many 3D apps use approximations and short cuts to make rendering time acceptable, didn't realise this one was one of them. It was useful to find out that 0% and off are not the same in the shader tree...not what I would have assumed.

As it happens...haven't got that far yet to notice some of the quirks of the program, I am having a crash course in Hexagon, Carrara pro and poser simultaneously....the learning curve feels like a cliff

but i am having fun

AWBenson · 15th February 2006, 23:14

The reason why the shader thinks 0% and none are different because when you make complex procedural textures, you will typically layer patterns on top of other patterns. In this case 0% means the color black, and none means it's tranparant to it's parenting (sub)channel.

steve_j · 16th February 2006, 06:45

These responses are helpful, but I think there's more to this problem. As I said in my first post, when I import the *.obj file, it has transparency set at 0-100% with a value of 0% (there is no child to "transparency -- see the first screen capture). If I set transparency to "none" the smudges go away. Then, if I then select "transparency" and set the value to 0% the smudges are still gone, but there is a subtle difference -- the 'transparency' portion of the shader now has a child that has a value of 0% (see the second capture). Apparently, the imported *.obj file has a different way of specifying zero transparency than Carrara's internal shader does, and this is somehow involved in the creation of the smudges.

Patrick210 · 16th February 2006, 08:03

2 things - are you enabling "light through transparency" in the render settings? The shader question is simple. When the object file is imported, the transparency channel, has a simple percentage value. When you change it to "none" and then try to change it to back to a value, you are in effect resetting it to the Carrara 5 Pro transparency default setup, which includes the Fresnel option. If you wanted to you could copy and paste a simple value channel in there from another part of the shader, but I don't think that would change anything really. It might be that GI is affected a little differently even with a zero value as opposed to none, that's why I asked about light through transparency. If that is true it's a little bit of a mystery. It doesn't seem like this is a big obstacle to getting a correct render, though.

15th February 2006, 00:24	#1 (permalink)
steve_j Spline Join Date: Feb 2006 Posts: 37	Rendering Problem I'm a new user of Carrara 5 and am having a problem rendering with global illumination. I have imported a model (from truespace-in obj format) containing 2 microwave 'horns'. I "creased edges" on the upper horn to make its surfaces look flat. I wanted global illumination so I loaded a background image (snowfield -- supplied with C5) and set the default light to zero. When I render the image using GI, (sky light checked) I get the first attached image -- with the strange smudges on the top horn. The smudges are not there when I use individual lights and no global illumination, but they are there no matter what quality I set for lighting or how many photons I use in GI. The texture for that horn has Transparency set at 0-100% with the value at 0% (this is how it imported). When I set Transparency to 'None" the smudges go away (the second image). 0% should be equivalent to 'none', don't you think? Also, the smudges only occur in parts of the model that have had edges creased. It would be an easy workaround to change Transparency to 'none' if the model was as simple as the images shown but there are many other parts and they all have this problem. This looks like a rendering or transparency bug to me -- has anyone seen this before? Attached Thumbnails

15th February 2006, 17:01	#5 (permalink)
andywright Extrusion Join Date: Jan 2006 Location: Oxfordshire, UK Posts: 154	sounds like you should report it in the bugs section __________________ Athlon 64 X2 4400+ Win XP Pro, 2 GB DDR 400 MHz Geoforce 6800GT Xtreme 256 MB. Carrara 5 Pro, Hexagon 2.01, Lightwave 8.5 Poser 6, DAZ Studio, Vu 5 Infinite, Bryce 5.5 www.wright-site.co.uk

15th February 2006, 23:14	#8 (permalink)
AWBenson Box modeling Join Date: Jun 2005 Location: Miami, FL Posts: 292	The reason why the shader thinks 0% and none are different because when you make complex procedural textures, you will typically layer patterns on top of other patterns. In this case 0% means the color black, and none means it's tranparant to it's parenting (sub)channel. __________________ Andrew Benson AKA: AWBenson www.awbenson.com andrew (at) awbenson (dot) com

16th February 2006, 06:45	#9 (permalink)
steve_j Spline Join Date: Feb 2006 Posts: 37	These responses are helpful, but I think there's more to this problem. As I said in my first post, when I import the .obj file, it has transparency set at 0-100% with a value of 0% (there is no child to "transparency -- see the first screen capture). If I set transparency to "none" the smudges go away. Then, if I then select "transparency" and set the value to 0% the smudges are still gone, but there is a subtle difference -- the 'transparency' portion of the shader now has a child that has a value of 0% (see the second capture). Apparently, the imported .obj file has a different way of specifying zero transparency than Carrara's internal shader does, and this is somehow involved in the creation of the smudges. Attached Thumbnails

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

15th February 2006, 01:28	#2 (permalink)
bwtr Brian Join Date: Jul 2005 Location: South Australia Posts: 2,097	Others will reply with proper info but it appers from earlier threads that the setting "None" or "Value 0%" are quite different on all items in the shader menu.

15th February 2006, 06:05	#3 (permalink)
Patrick210 Pixar want to hire me! Join Date: Apr 2004 Location: Florida, USA Posts: 549	Try turning off interpolation in GI.

15th February 2006, 07:02	#4 (permalink)
steve_j Spline Join Date: Feb 2006 Posts: 37	That did it! Thanks, Patrick. I still think it's a bug, but that is the least objectionable workaround.

15th February 2006, 17:07	#6 (permalink)
Patrick210 Pixar want to hire me! Join Date: Apr 2004 Location: Florida, USA Posts: 549	It's not a really a bug. Interpolation is really a down and dirty, quick sampling of the way the photons are working. It can be useful in some situations and it has worked exactly like this since GI came out in Carrara 3. Most everyone is aware of this except persons new to the program who we are happy to enlighten.

16th February 2006, 08:03	#10 (permalink)
Patrick210 Pixar want to hire me! Join Date: Apr 2004 Location: Florida, USA Posts: 549	2 things - are you enabling "light through transparency" in the render settings? The shader question is simple. When the object file is imported, the transparency channel, has a simple percentage value. When you change it to "none" and then try to change it to back to a value, you are in effect resetting it to the Carrara 5 Pro transparency default setup, which includes the Fresnel option. If you wanted to you could copy and paste a simple value channel in there from another part of the shader, but I don't think that would change anything really. It might be that GI is affected a little differently even with a zero value as opposed to none, that's why I asked about light through transparency. If that is true it's a little bit of a mystery. It doesn't seem like this is a big obstacle to getting a correct render, though.