One of the more requested topics that I get asked for is how to laser engrave photos on wood. Although a lot of your success is going to be dependent on the amount of testing that you do and the photos that you recieve from your clients there are some basic steps that you can take to make your chances of success a little more positive. There is nothing special here. All you need to remeber is that wood is porus and will not hold a fine detailed photo. So do not worry about getting rid of the detail in a photo. It make actually make your engraved photo look better.
Here is our Sample Image that we will use for this tutorial
First we need to import our photo in CorelDraw
Convert your image to grayscale
Our next step is to convert our image to grayscale. I do this for 3 reasons. The first is because our laser is going to convert the image to grayscale during the printing process we might as well work in grayscale ourselves. Also a grayscale image is 3 times smaller in file size than a coloured image. Thus our computer will process the image faster. Thirdly and most importantly when i do my adjustments to my photo the adjustments that I make will be seen better with the grayscale image than with the coloured image.
Select BITMAP | MODE | GRAYSCALE to convert our image to grayscale from colour.
Figure 3 shows us our image converted to grayscale
Our next step is to adjust the photo so that we can increase the contrast in our image. (For a more detailed article on increasing the contrast in an image see my article on increasing contrast in a photograph). Select EFFECTS | ADJUST | CONTRAST ENHANCEMENT COMMAND. See Figure 4
Figure 4 – Select the Contrast Enhancement Command
Figure 5 shows the contrast command opened. You need to “unlock” (1) the preview to allow you to preview the image. The original image is the left preview pane and the right preview window previewing what the original image is going to look like. If you can not see the preview windows click on the two little boxes at the top left hand corner identified as 2. Click the reset button to reset the command to its defaults (3).
The Histogram (4) shows us the spatial concentration of pixels in our image. The darker part of the image is the left side of the histogram and the right side is the lighter side of the image.
Setting the Contrast Command Window up
Once you have set up the previous window we can now make some adjustments to the image. Before I actually adjust the image let me point out a couple of commands that need to be identified in the window.
1. Auto -adjust – this adjusts the image automatically and is not something that we want to do typically
2. Shadow Adjustment – allows us to increase or decrease the shadow detail in our image
3. High Light Adjustment – allows us to increase or decrease the high light detail in our image
4. Gama Adjustment – Lets you accentuate the detail in low contrast areas without affecting the shadows or highlight areas
5. Samplers. Allows us to base our adjustments on sampled colours
Now that we know what each command is for let us look at what happens when we adjust the image. When we are working with the laser the two sliders we are concerned with are number 2 and 3 in our previous image. The slider for the shadows of our image (2) cause the darker parts of our image to become darker. The highlight slider (3) allows our lighter parts of our image to become lighter. You can see these in the previous figure.
Before we adjust the image we need to know what we are going to laser this image onto. This is because we will adjust the appropriate slider depending on what colour the finished image is going to be. In this example we will look at doing this image on a wood thus what is black will laser and what is white will not. This means that I will adjust the highlight slider more than the shadow slider.
To lighten the lighter part of the image slide the highlight slider to the left as per the next figure. You can see that the histogram is adjusting right and is becoming longer. This means that I am increasing the contrast of the image. The preview window shows me my adjustment (2).
Note: make sure that you lighten the image like mine in the figure below. Do not worry that the image is too white it will be fine. I need to create some distinction between the white and dark pixels. The red ovals indicate that areas that I want to go white. Also look at lightening up the chin.
If you want you can adjust the gamma so that the number becomes larger (say somewhere around 1.15). This will lighten up the whole image.
Adjusting the image to create more contrast
Our next step is to click on OK after the image is adjusted. Our next figure shows the adjustment
Our image has been lightened up.
Our next step is to sharpen our image by using the Unsharp command. Sharpening eliminates some of the shading in our image that will interfere with the look of our image. What the sharpening does is increase the contrast between the white and dark areas of the image by tricking our eyes. To sharpen our image go to BITMAP | SHARPEN | UNSHARP MASK.
Selecting the Unsharp mask command
The next figure shows the unsharp command opened. Again as in the contrast command click on the “lock” icon (1) so that any changes made will show in the preview window. If you can not see the preview window open it up by click on the 2 little squares at the top left hand window (2). Now take your Percentage slider (3) to 500 and your radius to 10 (4). Note: I typically move my percentage to 500. It is my radius that I need to be careful with as this can greatly effect your image.
Click the OK button. Note: just remember that the amount of your adjustments will differ depending on your image and what wood you are going onto. It is best that you spend some time practicing.
Our image is sharpened
Next we need to convert our image to black and white by using an error diffusion algorithm. Note your laser manufacturer has this built into their software but as usual I suggest you take this step as you can than see what is going to happen. First go to BITMAP | MODE | BLACK AND WHITE.
Selecting the Black and white mode
Our next figure shows us the black and black and white command. First make sure that you can see the preview images in the command. If not as per the last steps click on the two small boxes at the top left hand window (1). Next from the pull down window select the “Floyd Steinberg”, “Jarvis” or “Stucki algorithms” (2). Adjust the intensity depending on the image (3).
Converting our image to Black and White using an error diffusion
Once you are done click on the Ok button. Our next image shows the final image. Note: The image will look bad on your screen as the zoom level needs to be exact for it to display properly. This is why you need to make sure that you look at the image in the preview window.
Note: The coarser the wood the less printed resolution that you should use. For example if you are going on alder you may want to use 400 DPI. But on oak you may want 250. The coarser the wood the lower the resolution that you need to use.
Here are the Finished Images
Here are two examples of the image lasered on wood at 600 dpi and 400 dpi same powers and speeds on both