Alpha Channel, Trees, Vray - HELP

CurryPork

Hi forum, I need some alpha channel help. I don't know if it's a Vray setting or a Sketchup setting.

Basically, I have some 2D and 3D trees sketchup trees, but I cannot get them to render correctly in VRAY for sketchup. How can I fix the alpha channel?

Thanks

2D Tree

2D Tree rendered in Vray

3D Tree

3D Tree rendered in Vray

thomthom

You need to extract the alpha channel as a grayscale image. Then add that to the transparency slot in the diffuse channel. V-Ray doesn't read the alpha channel from PNG images, so it need to be separate.

CurryPork

How do you extract the alpha channel? I can't even find the PNG file from these trees. The 2D might be possible with Photoshop, but how would you extract from the 3D tree?

Gaieus

How did you get these trees? What the images used in them is needed is a clip map (if you can get the original png files, you can create these clips easily in PS).

CurryPork

Here are the trees. I got them either from here, the internet or the warehouse. But my point is how can you extract the PNG or the alpha channel from these sketchup files.

2D tree

3D tree

thomthom

Right click the material in the SU material editor, choose "Extract Texture Image". Save the file to disk and open in your image editor of choice to extract the alpha channel.

CurryPork

Thanks Thom, I tried right clicking everywhere and cannot find that feature.

thomthom

Sorry. Be in the list of materials. Not in edit mode. (The "Select" tab next to "Edit")

CurryPork

Thanks Thom. I learned something new.

I got the alpha channel out of the tree now. Do you know how to make it work in Vray?

I assign a PNG as a bitmap in the COLOR slot in DIFFUSE and the alpha layer as a bitmap in the TRANSPARENCY slot in the DIFFUSE. But when I render in Vray it's not working... any suggestion?

Thanks

CurryPork

OK, I got it to work... thanks.

chango70

So how did you get it to work?

CurryPork

I have it working for the 2D tree and this works for the 3D tree as well. So, just extract the alpha channel from the original texture as Thom described.

In VRAY, apply the original texture in the Color slot and the alpha in the transparent slot. Render and this solves it.

Thanks Thom.

chango70

Thx I just tried it myself and it works.

devran

Hi Fellowcombatants listen!!! First You download the tree from warehouse... click on the component open it then rightclick and save the png. then open in Photoshop and rightclick on the icon in the layers menu and choose choose pixels... change to channels menu and create a alpha channel... this channel is saveable as a new picture... rightclick on the alpha channel and save as a new picture... thats all.... ( sorry for all non Photoshop users)... ciao devran

tvicari

You guys rock . . thanks for the tips, works great I have been looking for this solution for a long time. Thanks for making an effort and sharing knowledge.

jdcarling

Hey all,

I read this post and have figured out how to create the alpha channel in photoshop for a tree, but cannot find the location to insert the png properly in the material editor - diffuse - transparency. I clicked the lower case, then switched the left panel to TEXBITMAP but coudl not insert the alpha channel PNG anywhere... any tips.

jdcarling

Hey All,

I read this post and have figured out how to create the alpha channel in photoshop for a tree, but cannot find the location to insert the png properly in the material editor - diffuse - transparency. I clicked the lower case, then switched the left panel to TEXBITMAP but coudl not insert the alpha channel PNG anywhere... any tips.

thomthom

In the Transparency slot of the diffuse layer - add a TexBitmp:

kalu

Hi thomthom:

I have this dilema, I read the post all perfect. I try to mimic the results and I want to know what I am doing wrong. I attach the tree and the images for the render. Please let me know what I am doing wrong. I use Sketchup Pro 8 and Vray 1.48.89. Some of the leaves show as a rectangular green. I have no Idea why.

Here is the link to the 3D model of the tree:

https://rcpt.yousendit.com/1023169415/e1236da1e739047eed35fa1248da71be

Thank you!!!!

thomthom

That's because you didn't map the backside of the faces. You can even see that in SketchUp.

I'm guessing you imported this from another 3d format?
Because of that you lost the backside information. Many other 3d apps doesn't display anything on the backside of faces. You have to explicitly enable it.

To quickly transfer UV mapping from one side to another, use this plugin: http://forums.sketchucation.com/viewtopic.php?f=323&t=18992&p=155759#p155759