In this article I’ll describe my workflow for texturing my mechanical creations. Using both Blender and GIMP, I quickly create color, bump and specular maps. Blender ’s texture paint is used to start the texturing. From here, I use GIMP’s layers and layer masks to quickly add more detail and create the bump and specular maps as well. The mesh I amworking with is my Retro Rocket Racer, it has already been UV mapped and has a car paint material assigned to it that I downloaded from: So let ’s dive into it!

A blank canvas:

Initially, my screen layout looks like this:

Quick texture technique-1.jpg

I have the 3D view, UV/Image editor, and the properties panels open. The current material is displayed and from here we can start working on the textures.
First up, we will need a blank canvas to start painting on. Left-clicking on the material’s diffuse color will bring up a color picker. Select “Hex” from the three buttons below the color wheel. Now the color values for the material are displayed as one set of letters and numbers (hexadecimal format). Mouse over the value and use [Ctrl+C] to copy it.
Now open GIMP and create a new image. For this project I used an image that was 1024x1024 in size.
Left-clicking on the foreground color in GIMP opens a ‘Change Foreground¡ Color ’ window. Move the mouse to the ‘HTML notation’ field and use [Ctrl+V] to paste the color value. Now use the Bucket Fill T ool to change the color of the image to match the color of Blender ’s material. Save the image with a meaningful name and in a format blender can use (I use .png format). This is our blank canvas.
In Blender, with a material assigned to the mesh, switch the Properties panel to Textures. If no textures have been created yet, the panel won’t contain much information, that ’s about to change.
Left-clicking on the ‘New’ button will create a new texture slot and we will be presented with a wealth of data.
Right below the texture ID name will be a ‘ Type’ selection box and left-clicking on that box will allow you to choose what type of texture we will be working with. Choose ‘ Image or Movie’ from the pop-up menú. Scroll through the texture panel to the ‘Mapping’ section to adjust a few settings.
‘Coordinates’ needs to be set to ‘UV’ (since the mesh has been UV-unwrapped) and upon doing so a new ‘Layer ’ field appears. Set that to ‘UVT ex’.
Scroll to the ‘ Image’ panel, click on the ‘Open’ button and select the new blank canvas image just saved from GIMP to load the image. Select the mesh in the 3D window and enter edit mode. Use the [A-key] to select all the vértices. In the UV Image editor ’s header, left-click on the image icon and select the image that was just loaded into Blender. Now our mesh is set up to use the new image as a color map.
In the 3D view, we have a few more settings to be changed. In the 3D view’s header. Switch ‘ Viewport Shading’ to ‘ T extured’. In the transforms panel [N-key] under ‘Display’, set ‘Shading’ to ‘GLSL’.
(Note: for this to work, your model will have to be lit by lights. I usually place a few ‘Point ’ lamps around the object to light it from all sides.)
We now have everything set up for Blender ’s texture painting tools.
In the 3D view, you can now enter Texture Paint mode. Select the ‘Brush’ from the tools panel, use the color wheel to select a color close to the one we will be painting over and turn the strength of the brush down quite a bit. At this point you need to think about what parts of your mesh will show signs of dirt/scratches and start painting them on the mesh. Rotate around the model, and paint the áreas where you want to add dirt/scratches. This is my result after a few paint strokes where I want dirt/scratches:

Quick texture technique-2.jpg

From the UV/Image editor ’s header select Image>>Save Image to save our work so far.
This will be the basis of the color map, so now it ’s time to move over to GIMP to refine it.

Into GIMP:

Once you’re in GIMP, load the color map just saved in Blender. After that, use ‘File’ menú >> ‘Open as Layers…’ to load in the UV Layout from Blender.
Now we need one more texture in GIMP and this one will depend upon the look we want.
Should this look be dirt, scratches or rustí I’ve decided on rust, so in GIMP go to ‘File’ >> ‘Open as Layers…’ and choose a rust image that ’s the same size or bigger than the texture we’re working on. Time to organize this mess…
Arrange the layers as follows: the UV Layout should be on top while the next layer should be the color map saved from Blender after texture painting. The bottom layer should be the image that has the look we are after, in this case the rust image. Right clicking on the color map layer opens a menú where we can select >> ‘ Add Layer Mask’ to add a layer mask. From the next pop-up prompt choose >>’White (full opacity)’. My layers in GIMP look
like this:

Quick texture technique-3.jpg

After creating the layer mask in GIMP, it is now the active image that will be painted on.
It can be a little confusing at first, as the active image in GIMP is outlined in white and the layer mask is white as well. Left clicking on the color map will make it active, left clicking on the layer mask (to the right of the color map) will make it the active image to be painted. This layer mask on the color map is hiding the rust texture layer below it.
Layer masks in GIMP are grayscale images that control the visibility of the layer below it.
The darker the layer mask is, the more transparent the layer mask is and the more visible the layer below it will become.
Likewise, the closer to white the layer mask is, the more invisible the layer below it will be.
Using the Paintbrush Tool, and using various shades of grey colors, brushes (airbrush style brushes work best here) and brush sizes, slowly work to reveal the rust texture following the guidelines on the color map from Blender’s texture paint. During this
process, keep changing the brush pattern often, (I have 8~10 grunge type brushes), to avoid a repeating pattern of the brush. The Smudge Tool is very helpful during this process as well by smudging away any repeating pattern created by the brushes.
When the layer mask has been painted enough to give a general idea of what áreas will be painted, switch over to work on the color map. On the color map, select the base color and paint over the guidelines painted in Blender to hide them. Then go back to the layer mask to finish it up. After a few minutes work on the layer mask, this is my image (UV Layout shown for reference):

Quick texture technique-4.jpg

The UV Layout layer’s visibility can be controlled by the ‘ eye’ icon on that layer. the UV Layout layer’s opacity can also be controlled via a slider at the top of the Layers window.
Save the image first in GIMP’s .xcf format, in case we wish to edit this image later. Now disable the layer that has the UV Layout on it by clicking on the ‘ eye’ icon. Make sure the color image and not the layer mask is active and save this image with a meaningful name and in a format Blender can handle (I save as a .png image, which doesn’t support layers).
GIMP will now prompt that .png doesn’t support layers, just left click on ‘Export ’ and at the next prompt left click on ‘Save’ to save the file. I generally use ‘ color ’ as part of the name, since this is our color map.
Next, right click on the layer with the layer mask and from the menú choose >> Show Layer Mask. Right click again on this layer and from the menú choose >> New from Visible.
Now GIMP has created a new layer that is just our grayscale layer mask. Make this the only visible layer (eye icon) and save the image with a meaningful name and in a format Blender can handle, (Again, there will be a series of prompts to click through).
This image is what will be used in Blender for bump and specular maps and I generally use ‘bump’ as part of the filename.
Speaquíng of Blender, it ’s time to return to Blender to finish up.

Back in Blender:

The image previously created in Texture Paint can now be replaced with the new color map saved from GIMP . In the Texture panel, with the current texture active, scroll to the ‘ Image’ panel and load in the new color map. With the 3D View set to Textured display (as previously described), the new color map is now displayed on the mesh. We aren’t done yet, remember the black and white image saved from GIMP?.
In the Texture panel, select the empty texture slot below the color map texture and left-clik on the ‘New’ button to add a new texture slot.
Just as before, set it to be an image texture, adjust the mapping settings, and load in our ¡grayscale bump map saved from GIMP . By default, this new image will affect the color of the mesh and will look really strange on your screen, so we need to make a few more adjustments…
Scroll through the texture panel to the Influence panel. Under ‘Diffuse’, uncheck ‘Color ’ and your display should return to just the color map since this texture no longer affects the color, (by default, new textures influence the color of the mesh). We need this texture to be our bump map and also affect the specular color. So under ‘Specular’, check the box by the ‘Color ’ and under “Geometry’, check the ‘Normal’ checkbox. The mesh may now look a bit distorted (or in my case, a lo distorted), but that can be fixed via the ‘Normal’ slider. The ‘Normal’ slíder needs to be adjusted to the point where the bump map barely affects the surface of the mesh. Since this is a rust texture, the surface of the mesh should only be slightly affected. I settled for a value of -.025 to give the mesh a slight indentation where the rust is.

Quick texture technique-5.jpg

In the real world, rust is never smooth. It can range from being slightly rough, to really blistering and bumpy. To achieve a bumpy blistering rust, use a positive value so the mesh is raised where the rust colors are.
Here’s a close up rendering of the results:

Quick texture technique-6.jpg

Taquíng it a step further:

This technique of using layers and layer masks in GIMP can be expanded further. I have used this method with a dark texture and used the layer mask to reveal the dark texture to add dirt to the mesh’s color map. I then duplicated the color and dark texture layers, merged them down into a single image, added a layer mask to the new image and a rust texture layer below it to add rust.
I then duplicated and merged these layers to produce a new image. A layer mask was added to the new image as well as a bright steel texture below that. I edited the layer mask to reveal the bright steel texture to produce scratches. I created bump maps at each step by displaying the layer mask, right clicking on the layer and choosing >> ‘New from Visible’ from the menu.
This can obviously become very complex in GIMP, but careful naming of the layers in GIMP can help you keep track of what each layer is for.

Final thoughts:

The aim of this article was to provide a basic workflow for creating bump and specular maps quickly using GIMP . This was a method I used while working in the older Blender 2.49.
With all the great work from the developers working on the new Blender 2.5x/2.6x versións, there have been a lot of great things added that I have not mentioned here. Now that Blender has the ability to display bump maps in the 3D viewport, bump maps can be painted in Texture Paint mode and the results can be seen on screen (it ’s almost like sculpting in fine details without using the multiresolution modifier).
One can also use custom brushes in Texture Paint mode and there is even an Add-on called ‘Material Utils’ that allows one to quickly switch which texture layer is currently being painted on as well as a few other goodies for texture painting. I regret I did not touch on these topics in this article, but now, thinking of all the texturing goodies in Blender, I’m beginning to think one could write a whole book on the subject!