An effective way to use texture images and stock photos is to turn them into brushes for use in your graphic editor. Both Adobe Photoshop and Gimp allow you to easily create brushes and maintain libraries of them. Brushes are a very effective tool for any graphic artist because you can easily change the size, opacity, and placement of them in your image. You can also change their rotation and shape very quickly. Different brushes can be used for common tools such as the paintbrush, airbrush, and eraser. I promise to post how to make a brush in Adobe Photoshop, but since I am on my laptop that just has Gimp on it, we will use Gimp! Before we begin, the image below shows a quick example of the type of cool grungy surfaces we can make using only the brush we will create in this example:
Now if you look hard at the above image, you will start to see a repeating pattern that changes size, orientation, and position as I just airbrushed our new brush onto a solid grey color a few times. With the use of a just a couple 'grunge' brushes, you can make a completely unique cracked surface for your graphic for use in your 3d program, website, or whatever. So let's make a new brush! I grabbed a Cement Texture that I think would make a good brush:
The only way brushes look good and can be used in multiple places around your image is when they fade nicely to 100% transparent. You don't want to see sharp lines from the edge of the image while using your new brush. Use either the eraser tool to erase or airbrush in a solid color that you can turn transparent later to smooth the areas of the texture you want to keep to transparent. I created a solid colored layer behind my brush layer so that I can see how it will turn out more accurately. Here, you can see that we want to keep the cracks in our cement and fade out the rest:
Brushes can be made in color and they can also be created using multiple layers that can be randomized, but for now we will just make the most common brush; a greyscale one. Now let's turn our main color to transparent under Layer - Transparency - Color to Alpha. Now we have a brush that is ready to be saved:
The most common type of brush in Gimp is a .gbr file. There are a few other types, but this is what I prefer. Just click Save-As and select the .gbr file extension and name your new brush. At this point, you can also pick a folder that Gimp searches for available brushes:
A dialog will pop up, asking you to name your brush and provide the default step spacing for it. The brush can be named something different then it's filename that Gimp will show in its brush library. The spacing is how many pixels Gimp will draw each iteration of the brush if you were to hold down your mouse button and paint your brush across the image. Here is our dialog where we name the brush:
The last step is to get Gimp to recognize your brush. Hopefully it was saved in a folder that Gimp will search for brushes in. The default folder is under Gimp's installation folder, then share/gimp/version/brushes. You can also add folders for Gimp to browse brushes under Preferences - Folders - Brushes:
Now click Refresh in your brush dialog box or restart Gimp to use your new brush! Again, I promise to do this same procedure with Photoshop and I will also begin making some brush packs available because they are so useful!