A comment appeared on one of my Photoshop 3D Painting YouTube video earlier in the week, so I wanted to address the basic concept this in a post.
When painting 3D models there is always a challenge when the designer/artists reaches the edge of a seam or a UV island and would like the texture to be carried over to the adjoining seam or UV island.
What does this mean. Typically when you view a 3D object on the screen you see the whole object in it’s entirety. Once you start painting things can go a bit wry. For example, paint may end up somewhere else on the model, of even in multiple places at the same time. Or depending on which mode is being used for painting (projection or texture), you may get a warning to suggest that the paint brush has hit a seam. The first example is pretty simple, and can typically happen when a UV island is overlaying another UV island (Remember UV references are just coordinates of a flat 2D reference to the surface of the 3D object. I’ll cover this in a separate post, then we can look at how to correct it).
This post will focus on the tools needed to paint across seams or UV’s islands. I’ll write another post about strategies on how to get continuous texture across a seam soon.
Let us take this example. Here we have a custom built chameleon (by Jon Reilly) and we would like to paint it. Understanding how the UV islands work, can be important for more complex painting and to get full control of the job in hand.
When the UV texture is opened you will hopefully the black lines. These lines represent the polygons that make up the model, but are laid down flat. To do this, the geometry of the model needs to be unwrapped and laid down flat. Obviously, this requires the polygons to be cut, which creates seams (i.e. take a tin and unwrap it, will at some point need to put the physical object at specific points to do it, this is the same concept). We can see that in this example Jon really knows what he’s doing and has taken lots of case to lay it out in a very logical way. However, as you can see on the diagram, when it’s examined more closely there are well placed seams that enable the textures to support the painting process.The area that we will focus on in this case, is the join between the tail and the body.
On the 3D model it looks like it’s on one piece (i.e a single shell), which it is! And this is great and will talk about it a little later on. When the 2D UV map/texture is opened, it’s clear, and it turns out that there are many individual connected parts. The joint area that we are focusing on, is less logical. In fact there is a connection between all of the UV Islands, just it’s not logical where, unless we understand how the UV map was created. To see how the seams work and put it into practice, select the 3D object window, and make the brush active (using the B key), then select a foreground colour. Within the properties panel of the brush, make sure that Projection mode is selected.
There are two modes :-
Projection Painting is suitable for painting multiple UV islands and across seams simultaneously or for painting the seam between two textures. However, in general, it is a lower-performance painting method and may result in cracks when you’re painting complex 3D objects.
Texture painting is targeted to single islands / seams, but will improve the painted texture quality.
Then select the 3D model window and paint directly on the model. You will hopefully see that the paint flows on the model and across the UV islands on the UV mode
This will demonstrate where the seams connect, and where Photoshop will lay the paint down and make the connection for you. As you know, both sides can be painted on, and the paint will appear automatically on the other view (if for some reason the paint is not updated, Photoshop lost the connection to the other canvas. Best thing to do in this case is close the texture down and re-open it from the model).
You can see that trying to do this direct on the 2D UV map will be challenging, and the UV map is laid down really well.
To put this into context, below is the UV before it was laid out properly in Zbrush. This is typically how UV’s are laid out. Imagine painting on this ! So the lesson is to have good and well laid out UV’s it will help in the painting of a model.
OK, so why is this important. Well it allows us to paint directly on a model without worrying about seams. And allows a continuous painting experience. This is even more important when working with textures, which I’ll cover this in another blog post very soon.
I hope you enjoyed this and it makes sense for painting on a 3D model with UV’s.
Other links – Photoshop Painting page