How To Paint Transparency Onto Your Image Texture?


There are several ways in which you can create texture maps for 3D objects in Blender. Perhaps the most creative of which is to paint your own custom-made texture in the image editor or the texture paint workspace. But did you know that you can actually make parts of your model appear transparent using the texture paint tool?

To apply transparency to a painted texture map, go to either the image editor or the 3D viewport in texture paint mode and go to the header bar. You will see an option labeled ‘Mix’ which represents the Brush Blender Mode. Change this to the erase alpha option and then draw onto your UV map to begin adding transparency.

This is a great way of creating transparency on your custom-made textures while having full control over where you want that transparent effect to be applied. You can also use pre-made textures with transparent channels or use math and color nodes with procedural textures to also achieve the transparent effect.

Creating Transparency On Any Painted Textures

If you have ever attempted to create your own textures using the paint tools in Blender then you will likely have been taken aback by the number of options that you have at your disposal. The problem is that many of these options are initially hidden from view.

Creating a transparent layer for your texture is as simple as enabling it from a single menu, but is easy to miss if you do not know it exists in the 1st place. Of course, you first need to make sure that your object has a UV map, and that you have at least created a base color map to work from before you can add transparency.

You can apply this option in no less than four different locations, as with many of the other tools Blender likes to give you multiple ways to do the same thing.

Image Editor Header

The 1st location is in the image editor. The header bar at the top has many of the basic brush parameters that you can edit to change the behavior of the brush, such as the base color.

Next to the base color, which appears as a color bar to indicate what that color is, you will a drop-down box that is currently labeled as Mix.

Image Editor Header

This is the menu for changing the brush blend type and is used to determine how paint layers are going to merge together when the brush is applied.

The menu is split into smaller sections based on how these different blend modes affect the brush. The last of which will have two options. One option is to add an alpha channel, and the second is to erase the alpha channel.

Erase Alpha Option

The one that we want is the erase alpha channel option, so left click to enable the blend type. If you begin painting on your UV map, you will begin to paint a transparent layer onto your object.

Image Editor Side Panel

The second location is going to be the image editor side panel, which houses many of the same options as the header bar but in a slightly easier-to-read format.

Again you are looking for the same menu for the brush blend type, which in the side panel can be located under the tab labeled as brush settings.

Image Editor Side Panel

It is more clearly labeled here as the blend menu, and if you have not touched it will also be labeled as Mix. Open up the menu and select the erase alpha option to activate that blend mode.

3D Viewport Header Menu

The alternative editor for texture painting is the 3D viewport, where you can preview the texture that is being painted onto your model in real-time.

You can also use the same paint tools in the 3D viewport as you can in the image editor by selecting the object and changing the mode to texture paint mode.

3D Viewport Header (Texture Paint Mode)

The only difference here is that you are now painting on the 3D object itself in the viewport rather than the UV map in the image editor.

3D Viewport Side Panel

Much like the image editor, the 3D viewport also has a side panel to access additional tools. If the side panel is not visible then you can press the N key to bring the side panel into view.

You will then need to go to the tool tab locating in the column to the side of the panel. Unlike the image editor, the tool tab is not the first option here.

3D Viewport Side Panel

There are some different options here to what you will find in the image editor but the brush settings remain. The first option is again for the blend type so switch this to the erase alpha mode.

What Does The Add Alpha Option Do?

You may be forgiven for thinking that the add alpha option is to tool that you need to use to create the transparent effect, after all, it involves adding the alpha channel.

But actually, it does the reverse in practice, restoring the texture underneath where transparency was applied using the erase brush mode.

As such this mode will only work on areas that have already been affected by the erase mode where transparency is created.

These different modes are formed as separate layers, which means that when you use the Add Alpha mode you are restoring the texture back to how it was before it was made transparent.

For example, say you had a cube with blue as the base color, and then painting sections of the cube green. You then use the erase alpha mode to create transparent holes in the green sections. If you then decide to remove these holes with the add alpha mode, what color do you think it will become?

The answer is green because that paint layer already exists under the transparent layer, which is removed with the add alpha option.

The Transparent Areas Of My Model Appear Black In The Render?

If you have simply connected your image texture to the base color of the Principled BSDF node in the shader editor, then it is likely that you will come up against a rather frustrating obstacle when attempting to render. All of the areas of transparency appear as black color, and you can’t see what’s on the other side.

The reason why is because while you may have told your material to use the textures color channels, you may not have told it to use the alpha channel as well.

To correct this, go to the shader editor where you should see the image texture node connected to the Principled BSDF shader via the color. For the image texture node, there is a second output labeled as alpha.

Connect Alpha Channel

Click and drag from this node and connect it to the alpha input of the shader node. After a couple of seconds, you should then be able to see inside your object through the transparent texture.

My Transparency Seems To Be Pixelated Around The Edges?

When you are creating procedurally generated textures using math and texture nodes, you are able to work with an infinite resolution to create perfectly smooth textures. However, with a painted texture you are working with the pixel count that you assigned when you first created the texture.

Limitations to your textures are most apparent when you try to add transparency to them. This pixelated effect around the edges can be very distracting.

The quickest way to correct this is to simply increase the resolution. To resize the image texture go to Image Editor > Image (Menu) > Resize, and then set the resolution on the X and Y axis to new values.

Transparent Hole Created By Texture

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