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...

 

[Juttie205]

When making stencils in photoshop I just use the pen tool on a 4096 page then save as a png is that correct or do i need to make a shape in photoshop so it's a vector shape?

 

[Juttie205]

Russell could I send you the file and see if it's a problem with the model or something I'm doing wrong?

 

[Juttie205]

Not sure what I've done wrong but when I export to photoshop the image is to small for template so nothing lines up was fine before so not sure what I've changed and help would be great

 

[Russell Sobie]

1) Stencils can be any sized image, but I like to stick to 4096x for all of them. PNG is fine. They are bitmaps, as in... just images. The vector stuff isn't going to come through as anything other than tiny squares no matter what.

2) If you want to put up your file somewhere for me to download, that'd be fine.

3) I don't know what you mean by the image is too small for template... When you do an Export Channel to PSD, it should export at whatever the layer texture size you've entered when you created the Layer. Are ALL of your layers 4096? I don't recommend choosing multiple sizes... not sure how that works out.

Once it is in Photoshop, if the image isn't 4096, then you did something wrong in Mudbox. If you are talking about "template" as in, the original wireframe you grabbed from Content Manager... I'd probably skip that step now. Let Mudbox export its own wireframe layer when you Export Channel to PSD.

 

[Juttie205]

As you can see here I exported the layer which is 4096 and my wire frame from original template is also 4096 but when I put the blue layer over it does not line up it's too small as you can see when its selected in picture

 

[Russell Sobie]

I'd go the other direction. Put the ambient occlusion layer into the PSD file you are exporting to instead. In my opinion, you should be working in that PSD back and forth until such time as you don't want to work in Mudbox anymore.

What looks like is happening is that you copied the blue contents from a single layer in the exported PSD and are trying to paste it on top of the "template" PSD. Try "Paste in Place" if your version of Photoshop has such a thing (I'm on a very old copy, and I have to do shinanigans to do the operation you are trying there). Or... you can just line it up manually after you paste it with your Cursor keys.

 

[Juttie205]

mate your a star it was paste in place now spot on thanks again

 

[Juttie205]

Have finished my first livery using all your guides made it bloody awesome so thanks could you tell me how your grabbing the picture from cm showroom at end of your video many thanks

 

[Russell Sobie]

Greenshot. Free replacement for Snipper Tool that does a lot of awesome things (such as allow me to capture most of the images in this very tutorial!)

Greenshot

Greenshot - a free screenshot tool optimized for productivity

getgreenshot.org

 

[Juttie205]

Thanks will take a look

 

[Juttie205]

With all your help and guidance these are my first 4 attempts many thanks again

 

[Juttie205]

Quick one once I export layer to photoshop and say do some touching up or effects etc how do I get it to show back in mudbox like in your videos does it need saving as something special??

 

[Russell Sobie]

If everything is set up correctly (I didn't do anything special or anything), when you Export Layer to PSD, it'll open the file in Photoshop AND Mudbox will then start watching that .psd file for changes. Basically any time you make changes to that .psd file Mudbox will bring up a dialog that will say something like "Update changes?" or "Re-import changes?" or the like. Just press the button that makes that happen, and it will bring your changes over, including any new layers you may have added.

 

[Jose$wervo]

a little off topic:
once a skin is completed, is there a way to assign a skin to a person so they get that skin every time they enter our race server?

 

[Russell Sobie]

Not sure. I race pretty much exclusively on simracingsystem.com where they have an automated SRSSkin app that people use to upload and download their skins automatically (with some minor folder setup in the skin folder).

I suppose it depends on how you have your server setup?

 

[Juttie205]

When I use the stencil tool to make shapes and delete parts it does not seem to make a clean edge its allmost like a faded edge feathered off if that makes sense. Can you change it like in photoshop brush tool for example you can change if it's a soft edge etc

 

[Russell Sobie]

Yup. You want to change your Falloff. I typically put it on "full" and leave it there since I do mostly all stencil work.

 

[Juttie205]

Brilliant thanks mate knew must be summit like that

 

[Juttie205]

I have exported a layer to photoshop to make some changes like putting a stroke around a shape as I would like a black line but it seems to want to include all the parts I have used the eraser tool on? And not just the shape I've made what am I doing wrong?.

 

[leotkowns]

Have you ever tried to skin the dashboard of a car? Like add a logo to it? Trying to find a tutorial on that. It struggling. Thanks