Using bitmaps to create reliefs for CNC routing

By René Giroux

Posted on Sunday, August 21st, 2022

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What is relief? To me, relief is like three-dimensional color. Just as you can add color to a line art layout to make it more appealing, you can add relief to a layout to add interest. You can add both of them to truly maximize a good layout. Make sure you troubleshoot your graphics first, of course, because dimension, like color, cannot save a defective layout.

I often say that relief adds as much to good design as color might. Here’s how. Think of an everyday object that has only one color—like a coin, for example. All the graphics, faces and lettering on a coin are very visible on this small object that cannot use contrast between colors to be effective. Think of a chocolate bar that has a brand name embossed on it. It’s all one shade of brown, yet all the details are there. How about the lettering on an aspirin or on your tires? All of these use relief to achieve readability.

If you want to learn more about 3-D software, you can contact tech support, who may well overload you with technical jargon, but here you’re going to get a simple example from sign maker to sign maker. It doesn’t really matter what software or what CNC machine you use to produce your work. Those are both just tools. I call all CNC router tables “fancy hammers” because that’s just what they are. Mine is an AXYZ 4008 series CNC router. (I like to tease my friend Dan Sawatzky comparing his choice of router table to mine, but that’s not the issue here. Luckily, we both use EnRoute Pro software to drive our tables, so that cuts down on the leg-pulling!)

Relief creates appeal

There are several ways to apply relief to a sign. Carving into the surface by hand or by machine is one. Sandblasting works, too. Even adding cut-out letters to a sign adds relief.

The available software packages all have different relief tools for you to play with. Making a cube out of a square, a dome out of a circle, or a letter from any vector shape is easy. You just have to learn the different options within the software and invest the time required to better yourself at it.

The approach I wish to focus on today, though, is adding relief using bitmaps. What is this? Well, follow along.

Bitmaps and router tables

Bitmap images are made of individual blocks called pixels that are arranged and colored differently to create the image. You can see these little squares when you zoom in to part of the image. From a distance, though, the colors and shapes in a bitmap image appear continuous.

Bitmap images can be used in color, but for us, it will be much simpler to keep everything in black and white with grayscales. From the start, the principle to understand is that the relief we want to create will be in proportion to the contrast between the darker and the lighter shades in our photo. Because I work in EnRoute, I can say that’s what happens in this program, but I’m pretty sure the other software packages function the same way.

Figure A

Using a small image (Figure A), 3-by-3 in. and 1-in.-thick with a flat relief, I add a bitmap image, which represents a white dot on a black surface. EnRoute will leave the black background as a neutral relief, and the white part will stand out if I choose to add to the relief (positive value) or as a hole into the surface if I choose to remove from the relief (negative value).

The height or depth of this white dot can be programmed and controlled. What’s important to understand is that the measurement is in proportion with the percentage of the grayscale value. Black is neutral or non-affected. White will be 100% of the programmed height, and a 50% gray would be half the height.

Figure B

That’s simple enough. Let’s try this one now (Figure B). We make four small rectangles of different shades on a black background. We export the file to EnRoute as a bitmap and apply it to a flat relief object once again. Let’s say that we program a height of 1 in. The first example we find will look like stairs going up because we chose to add to the relief. If we asked for a 1-in. relief, the white part will stand out 1 in. from the background and the 25% gray will stand out 3⁄4 in. The same logic will apply to all the other shades of gray. Should we choose to remove from the relief or ask for a negative value, the result from the same image would look like stairs going down.

Creating a basket weave background

Now, how does that apply to real life? Last summer I had a client who wanted a monument sign for a locally renowned day spa. The colors, typeface and logos were to reflect the website pages they had just spent a fortune on. (There goes the nice hand-done script!) Looking at their website, I saw a few images of natural things like rocks, plants and wicker mats. There was the texture I needed to make the sign come alive! They loved the idea.

At first, I tried using woven patterns generated by the computer. They looked too stiff. A hand-drawn one looked too uneven and cartoonish and didn’t suit their needs. The next day while at the hardware store picking up supplies, I passed a wicker chair in the home decor section. I ran back to the van, grabbed my camera and took several photos of the chairs under different lights and at various angles.

One of them suited my needs for this job perfectly. I brought the picture into CorelDRAW and changed it to grayscale.

Once in grayscale in CorelDRAW, I chose Bitmap Image > 3-D Effect>Stamping, then played around with it to create an image with very dark and very light highlights to maximize contrast, and thus relief.

I exported the new bitmap image to EnRoute and used it as a background texture to enhance the negative space in the format.


Here’s one of the sign panels in progress. Notice that the wicker texture in the background is already very visible without any finish on it.

Here’s a close-up after finishing.

The wicker background adds interest to an otherwise basic job. The faces are 4-ft.-by-6-ft. ovals of 20-lb., 2-in.-thick Corafoam mounted to an Extira fiberboard core. It was designed in EnRoute software and routed on an AXYZ 4008 series CNC router. This sign is finished with 1Shot enamels and acrylic latex paint and is mounted on red cedar posts with wood trim.

The sign itself is a relatively simple design. The clients didn’t want gold, scrolls or any other fancy elements. It had to be kept classy while using decorative elements that would not steal the show. This just goes to show how texture can add to the value and esthetics of a sign.

Those ideas can be found in everyday objects. All you need is an imaginative eye and a camera to capture images such as tree bark, bricks, stucco, rocks, wood grain, concrete, grass, fabrics and so on. With those ideas and a few clicks of the mouse, you can quickly and easily create your own library of 3-D reliefs. Let the fun begin!

Some of you might have seen my work in SignCraft in the past, or met me at a meet or sign show. As a French Canadian, writing a technical article in English is quite a challenge, so please bear with me. I’m a signwriter, not a writer. — René

René Giroux lives in Gatineau, Quebec, Canada.


This article appeared in the March/April 2008 issue of SignCraft. René notes that while plenty of technology has evolved in the years since then, this process is still relevant. “This is the basics,” says René, “and that never changes.”