Skinning Assetto Corsa Cars from Nothing using Mudbox and Photoshop

[Russell Sobie]

This Tutorial was originally posted over on the simracingsystem.com forums where I do all of my skinning. I was constructing it AS I was learning the process, so obviously some of this is going to be "not the best way" to do certain things. I was going to make a post just linking the original tutorial, but after asking permission to the folks here at RD, it was suggested that I just post the tutorial in its entirety here! That said, let's get started!

NOTE: I have added notices before or during the parts where it is SRS specific, like making sure your skin is under 10MB (a limitation of the SRS Skin Transfer App used to automatically share custom skins just before races start). Follow the red instructions so you aren't doing extra work where you don't need to!

Software Used

• Adobe Photoshop (with NVidia Texture Tools for Photoshop Installed) (or... with Intel Graphics' version of a similar Plugin that works better for more recent versions of PS)
• Autodesk Mudbox
• kn5conv.exe
• Content Manager
• Notepad++
• Greenshot

The Goal
Since it is almost the end of the current season and I don't know what cars are going to be used next season, I figured I'd learn on something that I figure will EVENTUALLY come up. So the McLaren 650 GT3 is what I'll be doing. The goal is to replicate my typical Red/Black two tone design, complete with a skull on the hood using the most efficient means... rather than just fumbling around with a wireframe texture in Photoshop like I have been doing.

Disclaimers

• I'm not a professional artist. I have a background in graphic design and some 3d modeling but make no claims to know the best way to do any of this stuff. This is just what I've learned jumping in head first.
• Also, Mudbox crashes. A lot. Save often!

Extracting 3D Model
I started by using a program called 3DSimED3. Unfortunately it only has a 20 day trial, and today it ran out. Normally in this situation I would just purchase a licence and call it a day, but I was curious if there was a better way to just get a 3D model out of the .kn5 files that Kunos includes in a normal installation of Assetto Corsa. My googling lead me to this youtube video: Assetto Corsa KN5 Converter & Download

I was unable to find the origin of kn5conv.exe, but I ran a few scans on it and it turned up nothing, so I gave it a try. Works great. Here's how _I_ would recommend extracting the model (as opposed to how the youtuber above does it):

1. Create a Workspace for your new skin outside of your Assetto Corsa file structure. Here's mine: S:\GameFiles\AssettoCorsaStuff\cars\ks_mclaren_650_gt3\workspace
2. Copy the mclaren_650_gt3.kn5 file from your Assetto Corsa installation into this folder (you can find it here: ...\Steam\steamapps\common\assettocorsa\content\cars\ks_mclaren_650_gt3.kn5)
3. Place an instance of kn5conv.exe in your workspace folder.
4. Drag the KN5 file onto kn5conv.exe and watch the magic happen.

The result is that in your workspace folder you will now have a number of file types that can be understood by a number of 3D software packages, such as Mudbox and Blender. I gave Blender my best shot, but couldn't figure it out and there was not a good tutorial I could find that would clue me into how it works. I did find one that was enough help so that I could get going in Mudbox, so that's what I'll be doing.

If interested, here's the youtube video I found that got me going:

Cleaning Model For Painting
Once you have an .FBX file for the car you want to paint, you can import it into Mudbox.

1. Open Mudbox.
2. File>Import...
3. Navigate to your workspace folder and import mclaren_650_gt3.fbx
4. Save the scene as a .mud file (mclaren_650_gt3.mud) in your workspace folder.

This is ALL of the geometry and a bunch of other nodes/objects that you will not need for the purposes of creating a livery. So we must now delete all of the stuff we don't care about. This will speed up performance within Mudbox, as well as avoid Mudbox wanting you to add additional materials every time you attempt to paint on a different mesh. In other words, we want to avoid painting on the windshield when what we want to do is paint on the car's body. Here's what I did to go through everything:

1. Change to the Object List.
   
   
   
   
2. Hide everything in the Object List
   
   
   
   
3. Show only Geometry
   
   
   
   
4. Switch to Object Selection, and turn on Mirror on the X axis.
   
   
   
   
5. Select geometry in the scene view that you know you will not be painting. Windows, tires, brake discs, windshield wipers, whatever. All that should be left are the panels of the car you want to put your design on.
6. Save your .mud file. You may want to save it as a different .mud file than the original, in case you realize later you deleted some part of the geometry you actually wanted!

The end result should look a bit like this:

...continued next post...

 

[Nrde]

I have in Mudbox some objects (little plates or srews) which are not generated correctly at the export to Photoshop.
View attachment 333002 View attachment 333003

Just paint the squares on whatever color you want? You want the smaller squares to be what color? I guess the the texture on mudbox is 2 layers or?

 

[SuperMario333]

Are you saying you painted green rectangles on both the left and right side of that bumper and it only shows up as a single rectangle in Photoshop?

Exactly that's my problem.

Do you have the Audi R8 LMS 2016 car in AC? Maybe you can try at your car to paint this little objects (rectangles) on the rear bumper. For a test it should be enough to select this both objects, to paint it und export it.

What are you actually wanting it to look like on the car itself?

That the entire rear bumper is green without the grey rectangles. Currently it looks so

P.S. Sorry for my english !!!

 

[SuperMario333]

Just paint the squares on whatever color you want? You want the smaller squares to be what color? I guess the the texture on mudbox is 2 layers or?

Yes, bumper and rectangles are different objects. Therefore I export separately the painting layer for the bumper and the rectangles to different *.psd files. For the bumper file everything looks good, but for the rectangles file I get everytime only this huge green box.

Thank you too

 

[Nrde]

Yes, bumper and rectangles are different objects. Therefore I export separately the painting layer for the bumper and the rectangles to different *.psd files. For the bumper file everything looks good, but for the rectangles file I get everytime only this huge green box.

Thank you too

It's only once in the texture file (the psd/dds file) The same way you only have one file for the rims of the 4 wheels.

How does your EXT_Details2.dds file look like? Or do you have one?

 

[SuperMario333]

No, I don't have one. Sorry, I don't knew that the special parts in a separate file. Looks that's my issue. And how can I generate that file to paint these parts with Mudbox? It looks to a screenshot from Content Manager. But I was never in this menue. Until now I have only worked with Mudbox together with the guide from Russell

 

[Nrde]

But I was never in this menue. Until now I have only worked with Mudbox together with the guide from Russell

How do you extract the mudbox model, because I get a texture directory inside the car's directory when "unpacking" the kn5 file. So you can just open that file from there, change the colours, exports as DDS and copy that into the appropriate skin directory.

I think exporting from CM works only on registered version (which I suggest you do in any case, as it's excellent and should be supported).

 

[Russell Sobie]

The kn5 extractor linked in this guide does the same thing as CM's kn5 unpacker; it creates a texture folder where you can find all the textures used on the geometry in case that texture is not represented in the skin folder. What was confusing to me is that your attachment in "Plate PS result.jpg" looks exactly like what Ndre has identified as EXT_Details2.dds. So it looks like you almost got there on your own!

If you've deleted the texture folder after unpacking the kn5, just re-extract it and find it again. Then, if you simply don't want that particular rectangle to be visible from EXT_Details2.dds, you can just have that rectangle be entirely black in an alpha channel. That should allow the main skin's texture information to show through.

Or you can just paint that rectangle the same exact color as the rest of the body in EXT_Details2.dds. Same result, I think.

 

[SuperMario333]

Great, thank you very much to you two !

So you can just open that file from there, change the colours, exports as DDS and copy that into the appropriate skin directory.

When you write just open, change and export .... do you mean with PS or Mudbox ? I hope my project is then finished. Only with your help!!! I'm very happy.

 

[Nrde]

When you write just open, change and export .... do you mean with PS or Mudbox ? I hope my project is then finished. Only with your help!!! I'm very happy.

DDS is just a bitmap file. So PS (or gimp or some other DDS capable bitmap editor software).

 

[Juttie205]

I have just installed mudbox after watching the video and I'm having a issue with image browser as I have a folder on my desktop that has my jpeg and png files in and I can open these files fine in photoshop. If I go to this folder through mudbox image browser it show the folder as empty??

 

[SuperMario333]

and you have used the Refresh Button (left from Bookmarks) ?

 

[Juttie205]

Been following guides and been great but cannot get clean lines on my stencils no matter what resolution I do them in they allways seem pixelated any help would be great.

 

[Russell Sobie]

Things to try:

• Paint on 4096x paint layers.
• Use 4096x textures for stencils.
• Make sure your car model is scaled up to "adequate scale"... I usually scale up the model such that it takes up 4 of the grid boxes around 0 0 0 in the Mudbox scene.
• Focus the geometry (look at and hit F) before starting to paint a surface.
• Try different distances away from the surface when you line up the stencil.

I can't think of anything else I do... and I do probably 90% of my painting using stencils at this point.

 

[Juttie205]

Thanks did try and follow the guide on front page with scale up the image struggled to get all parts to scale even though they are selected but did find if I held mouse button down could turn everything yellow and scale that way is that way ok?.

 

[Juttie205]

The bottom of the orange on nose section is showing issue im having and that's using the stencil that is already in mudbox I cannot get a crisp line and that's with layer set to 4096

 

[Russell Sobie]

I use that specific stencil all the time. Sorry... I don't know what to tell you.

 

[Juttie205]

I know been following your vids on youtube I dont understand it

 

[Juttie205]

As you can see from this pictures the stencil does not look to bad but when I brush onto car it looks awful that's with model scaled upto 4 squares and pressing f key

 

[Russell Sobie]

That might be the car's UV mapping causing it. If the mapping for that part of the car is really small you won't get good resolution with anything. What does it look like with a tiny brush (no stencil)?

 

[Juttie205]

Not tried it with a small brush will take a look