The word itself “UV Mapping” might seem intimidating and complex for so many people, giving the impression of something super technical and complex, while UV Mapping is indeed not easy but getting your head around the basics is fairly simple.
In this article, I will try to explain to you UV Mapping in simple words, for some of you who already know a bit about it, it will be a good refresher and for people new to it after reading this article you will have a general overview about it and also ready to do your first UV Unwrap!
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What is UV Mapping?
UV Mapping is the process of taking a 3D model and flattening it up and spreading it so we can have a 2D version of it in order to apply 2D textures directly on it.
So let’s say we have a 3D sphere and we want to put a 2D texture of an image we like, now the sphere is 3D and the image is 2D and in order to apply the 2D image on our 3D sphere we need to have a 2D version of the 3D Sphere flattened in order to apply our texture.
But what is the term UV, well it’s simple just like in the 2D space there 2 dimensions the X which is horizontal, and the Y which is vertical.
In the texturing space, we have 2 dimensions as well U and V also U is vertical and V is horizontal, the process of UV mapping is creating a map version of a 3D object on a UV space from 0 to 1 (image below showing the UV axis in the UV editor).
Types of UV Mapping
There are many types of UV mapping, the goal is one, to Unwrap our 3D object so we can apply 2D images on it, but the types correspond is the easiest way of achieving a UV Map depending on the type of object we are UV mapping.
If we want to create UV mapping for an object that is fairly flat, like a terrain or a piece of cloth or walls..etc then it’s best to use Planar mapping.
Planner mapping is using a Plan reference object in order to UV map our object because it has a similar shape and form to a plan (image below showing how we chose Planar mapping and apply it to our plan object).
As the naming suggests this type of UV mapping is for cylindrical objects for example poles, fingers, bottles…etc one thing to note here is when you apply the Cylindrical UV mapping or any type of mapping you will see a gizmo in the viewport.
This gizmo is a temporary object that you can manipulate, move, rotate, and scale to fit the object you are trying to UV map. The effect can be seen directly in the UV editor as you are manipulating the gizmo.
Below is an image of the Gizmo
Spherical Mapping can be used for any type of spherical object for example balls, planets… etc also after applying this type of UV mapping you will a sphere gizmo appearing where you can manipulate it and even make it half-sphere in case the object you trying to UV isn’t 100% spherical.
This type of UV mapping is mostly used for objects that have a box shape this could be buildings or frames…etc
Automatic UV Mapping
This type of UV mapping is quite interesting, as we have seen from the Planar UV mapping, one plane gizmo is projected onto our object with this type of UV mapping you can have several planes surrounding the object to be projected onto your object.
This is very interesting because then you will be able to capture your model from different sides and you won’t have any hidden areas that are not projected.
Of course, you can increase the number of planes to whatever number you like but be careful as the higher the plane number the smaller the UV islands you will have to deal with later.
UV Mapping Techniques
Manual UV Mapping
So far we have seen how we can use primitive UV mapping techniques and understood that basically, UV mapping is trying to project a 3D object on a 2D plane.
In the real world, there are objects more complex than a sphere, a plane, or a cylinder, actually organic objects are formed by the combination of primitive shapes, for example, a head is a sphere with a cylinder as a neck, and spheres for eyes, etc…
This is where we would want to do manual UV mapping, and to be honest I prefer using manual UV mapping all the time as I will have more control and it tends to be very straightforward.
Manual UV mapping is the process of selecting seams and then unwrapping our object based on those seams.
What are Seams? well, seams are the areas where your mesh would be cut, as you recall we have a 3D object, and in order to lay it down on a 2D plane we can cut it at some point in order to spread it. The area you choose to cut is what we call Seams.
In reality, seams are normal edges, any edge in our mesh can be a seam if we choose it to be, what we have to do is only select and select from the menu “Cut” and you will see that edge turn to white telling us that this is now a seam.
Where to place Seams?
So how do I know where to put the seams? It’s simple, look at your clothes now, yes your own cloth! you shirt lift your arm and look at the bottom of your sleeves you will see a line that goes all the way to the wrist well that line is a seam, this is where the sleeve was stitched from a plane piece of cloth.
Seams are usually placed in hidden places, in the back of the head, under the arms, or anywhere that is less likely to be shown to the camera because sometimes they can visual issues and we would like to hide them as much as possible.
Below are images where I would place seams on a 3D character (the white line is where the UV is, and it won’t show unless you have the UV editor open).
UV Mapping Best Practices
Minimizing Texture Distortion
First, let’s define texture distortion, in the instance where you create your UVs but you don’t lay them, for example, say you are doing UVs for a character with horns and you do not cut out the horn and insert some seams to lay it out properly.
What happens, in this case, is the texture in the horn region would be very much distorted because, on the UV space, it’s a very small space but on the 3D object it’s much bigger because there is X Y, and Z so the texture in that region becomes distorted.
We can clearly see that if we apply a checker texture, you will see that the checker gets very small and distorted in that in that comparing to the rest of the characters and this would results in unwanted visuals.
Optimizing UV Layouts
There are lots of optimization practices for UVs and it depends on what industry you will work in, whether its animation or Gaming, for example, let’s start with some optimization good practices in the gaming industry:
- Have as less UV islands as possible
- Mirror UVs as much as possible.
- have at least 5px padding (dilation) between the UV islands to avoid any visual seams.
- Plan your UV layout beforehand, especially when doing Building upgrades.
When it comes to the animation industry it’s much more flexible as there are no performance restrictions, I do advise even using UDIM (meaning not just 0 to 1 UV space but you can even go more like the image below from the basemesh that I use.
Using Overlapping UVs
You can use Overlapping UVs in gaming as that will save you space and will make your textures smaller in size, But if you want to have a backing workflow beware of this practice as overlapping UVs will end up in black and UV backs.
My advice in that direction is to move the similar UV islands to another UV tile 1 to 2 for example in the same position that way you save space and it won’t cause you any problems with the backing, the image below is for clarity.
UV Padding (Bleed/Dilation)
I want to quickly go over what padding is because we can’t talk about UV maps without mentioning and explaining exactly what padding is.
Padding is taking your texture border and expanding them by 3 or 5 pixels, this means we take whatever color or hue at that point and expand it more, the reason we do this is to avoid having black lines on our 3D models when these islands meet.
Padding, Bleed or dilation terms can be different from one software to another but the meaning is one, in the past, we used to do this by hand but nowadays with software like Substance Painter it is an option that you can choose and it will be done automatically for you.
Below is an image showing the padding area growing beyond the UV borders.
UV mapping is not something artists are very fond of, it’s a very noncreative process but a very much-needed and essential one. Some artists find it fun and a break from the creative work, and some even enjoy it as they can go all in planning and have the perfect UV layout.
If you want to get deeper and learn more about UV Mapping check out this course – Link Here
In all ways, UV mapping should be planned well and executed well in order to have an easy 3D texturing process and a very performant 3D asset.