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...

 

[SuperMario333]

and here the sdk folder. also no **.kn5 files

 

[SuperMario333]

Sorry Guys my mistake. The purchase of the Porsche Pack in Steam was is aborted with a failure and not successful. For all other bought cars I have the *.kn5 files.

Sorry again.

 

[Russell Sobie]

Glad you got it sorted. There is another way to get the files out of the kn5 files without using that hack, and that is using Content Manager. Michael Martin over at the simracingsystem forums figured it out. Check out his post over there at http://www.simracingsystem.com/showthread.php?tid=6557

 

[Nrde]

http://www.simracingsystem.com/showthread.php?tid=6557

Do I have to download something as it's not showing up automatically. I have autodesk fbx converter installed already.

 

[Nrde]

For others not seeing the converter, restart content manager (or I think that made it appear to the list)

 

[SuperMario333]

Hello Russell,

I have a question to the export from Mudbox. I understand that every geometry have his own paint layer. But how can export all painting layers together? My *.psd file have everytime only one paint layer. What I do wrong? In your tutorial it looks that you export all layers.

thx
Mario

 

[Nrde]

Hello Russell,

I have a question to the export from Mudbox. I understand that every geometry have his own paint layer. But how can export all painting layers together? My *.psd file have everytime only one paint layer. What I do wrong? In your tutorial it looks that you export all layers.

I would think having one geometry layer exported as single paint layer would be the preferred option. Just open them up in photoshop, paint.net, gimp etc and adjust the layers as desired. But maybe you have more simple work flow in mind...

At the moment I don't have mudbox installed, but I think if you select multiple layers, right click and choose "export selected" you can at least export multiple psd files at the same time. You may also try to combine the layers in mudbox and then export the combined layer.

 

[SuperMario333]

thx@Nrde

I think that's my mistake. I thought, in the * .psd file, all painting layers are together - not just one. That means I must merge with Photoshop (and not Mudbox) all of these separat exported *.psd files together to an main skin file?

 

[Nrde]

thx@Nrde

I think that's my mistake. I thought, in the * .psd file, all painting layers are together - not just one. That means I must merge with Photoshop (and not Mudbox) all of these separat exported *.psd files together to an main skin file?

That is at least how I do it, combine them in photoshop etc. and then export them as dds.

 

[Russell Sobie]

My preferred method of exporting the final dds file is to use an Action in Photoshop. I'd recommend googling "creating Actions in photoshop" for a good how-to, but here's a good list of commands to do in a row once you have your "multi-layer" psd ready to export to a dds:

1. Make sure the current active layer has some content in it.
2. Create a new Action.
3. Name it something clever and hit Record.
4. Ctrl-A (Select All)
5. Ctrl-Shift-C (Copy Merged)
6. Ctrl-N (New)
7. Ctrl-V (Paste)
8. Alt-Ctrl-I (Image Size)
9. Resize down to 2048x2048 using Bicubic Sharper (reduction) Resample method, or to whatever size you want your final image size to be. I typically work in 4096x and then resample down to 2k for exporting).
10. Shift-Ctrl-S (Save As...)
11. Save over the .dss file that makes your body or skin file for the particular car under your skin folder (with the appropriate .dss file format selected from the Save As dialog, of course).
12. Ctrl-W (Close)
13. Stop recording the action.
14. To the left of the "Save" command in the list of steps, click the "Toggle Dialog On/Off" button to tell the action to show you the Save As dialog every time you play the action.
15. Make changes to your source .psd file, and next time you want to export, just replay the action, and point to the file you want to save it to.

 

[SuperMario333]

Hi Russell + Nrde,
I have a question how do you paint objects which have to be turned before painting. As stencil I have a white rectangle. I know how I can rotate the stencil. But the result on the object looks very bad, because the straight line has a lot of steps. I mean this is an Alias-Effect. How do you paint straight lines which have to be rotated on the object ? Attached an example what I mean.

Thanks again
Mario

 

[Russell Sobie]

You are talking about the pixelation of the paint? Seems like one thing you can do to is up the working resolution (see a few posts above). Another would be to make sure you are using high enough resolution stencils. I think the distance away from the geometry of the surface from the camera before you paint down something also has something to do with how the stencil is applied, but I'm not sure.

And finally, check to see if your falloff is not a solid block. I don't have Mudbox on the PC I'm on right now, but I'll see if I can't get a screenshot of what I'm talking about when I get home this evening. You want it to be a linear or a slerp fall off. A solid block falloff may be causing that pixelation.

 

[SuperMario333]

Thanks Russell ! I mean the steps (jagged edges) on the white border. I'm not sure if I translate correct the effect from german. English Wikipedia says "Jaggies" to it. This effect is only if I rotate the stencil. In your videos I have never see this phenomenon.

 

[Russell Sobie]

They are definately there... it's just I start with a 4096x4096 texture to paint on, so you have to zoom in real close to see them.

https://imgur.com/cXU9Oic

Here's the same stencil used at the same angle and scale but on three different sized texture layers in Mudbox. The difference is striking.

https://imgur.com/F0hgMHD

The stencil is a 2048x2048 white square png file only. So that might be something to look into as well. Hmm... let's try a 256x square stencil.

Nope... that didn't seem to make much difference at all, actually (256x stencil on the left on the same layers as the corresponding squares on the right).

https://imgur.com/r8R7khx

So basically my advice is to work on a 4K texture and then downscale in Photoshop or whatever after you are happy with the results. Good luck!

 

[SuperMario333]

Great, thank you very much for your explanation. This was the reason. I used for the rectangle only a size of 2048.
Unfortunately now I have the next problem. In Photoshop every layer looks correct but if I export the *.dds file (DTX5) and use in AC there are many objects with miscolors. Therefore I have imported the before generated *.dds file in Photoshop. In this imported file the miscolors are good to see and it is not surprising why AC shows this failures. Do you have an idea what is going wrong now?

For better understand I have uploaded my original *.psd file.

EXT_skin00.psd

drive.google.com

Thank your very much again!

 

[Russell Sobie]

Looks like the problem is that you have an Alpha channel in that file you don't actually need (since it is all white). I was able to delete the channel and export as DDS and it looks like the original PSD still.

Additionally, I stopped using the nVidia version of the DDS plugin a while back as it stopped working with the later versions of Photoshop. I use this now: https://software.intel.com/en-us/articles/intel-texture-works-plugin

(I updated the original post with a link to that as well)

Hopefully this will fix you up!

 

[SuperMario333]

Hello Russell, thank you for the help and the hint to the other software. I think my failure was selfmade and very stupid. I had unselect the main layer inside Photoshop and therefore the skin had no background. That led to the miscolors at the *.dds export. Sorry for the circumstances.
I hope to have the last question to you now. I have in Mudbox some objects (little plates or srews) which are not generated correctly at the export to Photoshop. Do you have an idea what I do wrong? Attached an example for plates on the rear bumper. The correct paint layer is for the export selected

Thanks
Mario

 

[Russell Sobie]

Likely those square bolts/rivets are part of the geometry of the car itself, and might be assigned a generic material (like chrome or "metal" or something like that. Those are usually like 32x32 textures somewhere, where if you change the texture a little bit, parts all over the car will change (which usually isn't what you want).

I can't tell for sure from your first screenshot though... but that's the only reason I could think of that there would be blank squares at the corners of that green rectangle.

 

[SuperMario333]

Oh, I think there is a misunderstand. It is very interesting what you describe about the square bolts/rivets. But my main issue were the green plates (only as example). On my picture from the rear bumper you see two plates they are painted in green. These plates are together on one painting layer. If I export these layer to Photoshop I will get the showing result with only one huge green rectangle. Until now the export were at no time a problem. This is only happen with any special objects.

 

[Russell Sobie]

Yeah, something is lost in translation, I'm afraid. I'm still not quite understanding. 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?

Or how about a different tactic: What are you actually wanting it to look like on the car itself? I am just not sure what the problem is.