It's time to put your laser engraving and cutting machine into practical application! To unlock the potential of your machine, let’s begin with one of the laser’s most basic applications, engraving pictures.
In this episode, we would like to go through the whole process of laser engraving a picture with you, including material preparation, picture selection and editing, and work parameter configuration.
1. Prepare a Material
In the previous episode, Material Selection Guide: How to Choose a Proper Material for Laser Processing, we have introduced some commonly used materials for laser processing and the principles for material selection. Ensure that the material is safe for your health and the environment and that your machine is capable of engraving it. In addition, to engrave a clear picture, we recommend you use a material that has the following features:
- Flat top surface
As a picture is two-dimensional, it can only match a flat surface. If you engrave a picture on an uneven object, the result would be distorted. Besides, a laser engraving and cutting machine usually works with a fixed focal length. During engraving, a level surface enables consistent focusing, and thus guarantees uniform engraving effects.
- Fine and smooth surface
A fine and smooth surface allows more details of a picture to be presented. If the material you want to use doesn’t feel smooth, you can try to polish it. Avoid using porous materials; otherwise, the result will be blurry.
- Light color
Generally, the laser beam engraves materials through burning and makes the surface of the material darker. When engraving on a light-color material, the differences between the lightest and the darkest area could be more prominent, allowing more color gradients to exist in between.
Based on these considerations, we choose basswood, which meets the above requirements and is inexpensive and easily accessed, to demonstrate the process of laser engraving a picture.
2. Select a Picture
Picture selection is key to the success of laser engraving. A picture with high resolution and contrast would be our first choice since it contains more minutiae and objects in the picture are more distinguishable. Besides, to retain more details in the engraving product, it would be better to use a picture that includes a lot of transitions from light to dark and doesn’t contain large blocks of solid color.
Understanding the reasons why we choose a picture that has a high resolution, high contrast, and rich color gradient without large blocks of solid color, now let’s see how we can identify a qualified picture.
- High resolution
Image resolution is the detail an image holds. Images are made of tiny pixels (picture elements), or squares of color. Image resolution can be measured in pixels per inch (PPI) or dots per inch (DPI).
High-resolution pictures are at least 300 PPI or 300 DPI, appearing sharp and crisp. This resolution makes for good print quality and is pretty much a requirement for any picture that you want to reproduce.
Just because a picture looks good on your computer screen doesn’t mean it has high resolution. You can’t tell by the length-width dimensions, either. Heavy file size can be a clue, but not in all cases. A simple way to check image resolution is to open up the picture in an image program and view the file properties. You don’t need a fancy program to do this; most computers come with a basic image editing program that will do the trick.
- High contrast
Contrast is the degree of difference between two colors or between the lightest and darkest areas in an image. A high contrast picture features a big difference between light and dark, while a low contrast one has colors close in tone. If a picture is plain white, there are no differences in its color, thus the contrast is zero.
Although it seems easy to distinguish the light from the dark in real life, it may become a little bit tricky when it comes to a static picture. Take the following two pictures as an example, can you tell which one has the higher contrast?
Picture 1 has the higher contrast. Have you got the right answer? Here is a simple way to help you find the contrast differences between pictures:
(1) Prepare a screenshot software.
(2) Respectively cut out small squares of the lightest and the darkest areas from the selected picture. Then, juxtapose the light and the dark squares, so that you can easily see the contrast.
(3) Repeat Step (2) on another picture to get its contrast samples.
(4) Compare the contrast samples from different pictures. The larger difference between the lightest and darkest squares from a picture, the higher contrast the picture has.
- Rich color gradient without large blocks of solid color
When engraving a picture, the laser cannot reproduce color. Instead, it creates different levels of light and dark by controlling the amount of energy emitted, and thus recreates the picture. With a lot of transitions from light to dark in a picture, the monochrome engraving product will be more vivid. Conversely, if a picture contains too many large blocks of solid color, the engraving result may appear flat and dull.
3. Edit the Picture
The purpose we edit the picture is to emphasize the subject and sharpen the edges, producing a clear and distinctive engraving result. It does not require a lot of complex photo editing skills to achieve the effects we want. The operations we need to perform on the picture mainly include cropping, adjusting contrast and brightness, sharpening. You can use any photo editing program that includes these basic functions. Here we use the free open-source raster graphics editor, GNU Image Manipulation Program (GIMP) for demonstration. Now, let’s open the picture in the editor and get started!
(1) Crop the picture
Crop the picture based on your need.
(2) Desaturate the background
By fading the background, we can avoid background overpowering the subject. In some cases, if you don’t need the background, you can also directly remove the background.
First, we need to isolate the main subject from the background. We can do this by using the free select tool to trace the subject out.
Then, select the background, reduce its contrast and make it lighter.
(3) Reduce the shadows
Shadows usually cause darker burning during laser engraving. If there are too many shadows on the main subject, it may cause the final engraving product to look dirty.
Select the main subject, and then adjust its shadows and highlights. By increasing the exposure of the shadows and adding more highlights, we can get rid of some heavy shadows.
(4) Sharpen the subject
After adjusting the shadows and highlights, the overall color of the subject appears bright. But this is still not the final effect we want. To make a distinct engraving, we need to make the edges more clearly defined.
First, add more contrasts, to make the lines of the subject more pronounced again.
Then, sharpen the image, making the image looks crisp.
Finally, we get the picture suited for laser engraving. As you can see, compared with the original image, the edited one has a weakened background and a well-defined subject. Now we can save the picture and export it as a .png file. If you use other image editing programs, be careful not to compress the picture when saving it.
4. Start Laser Engraving
Here we come to the last step, engraving the picture on the selected materials. Depending on the laser engraving and cutting machine you use, the procedure for starting laser engraving may vary. In this step, we will use Snapmaker Luban to transform the picture into a G-code file and use Snapmaker 2.0 1.6W Laser Module to do the laser engraving job.
(1) Import the picture to Snapmker Luban
After you import the picture to Snapmaker Luban, you can resize and rotate it, adjust its position on the coordinate, and transform it to a greyscale image.
(2) Select Movement Mode
When creating the toolpath, you can select the Movement Mode, including Dot-filled Engraving and Line-filled Engraving. Dot-filled Engraving takes more time but results in a more detailed image. To pursue a better engraving quality, we use Dot-filled Engraving as the Movement Mode.
(3) Set Laser Power and Dwell Time
Both the Laser Power and Dwell Time directly affects the engraving result. The higher the Laser Power and the longer the Dwell Time, the darker the engraving color.
We can use the control variate method to find an optimal combination of Laser Power and Dwell Time. The engraving pattern with the darker color and without excessive charring or depression on the workpiece surface is the best result.
Finally, we set Dwell Time to 5 ms/dot, and Laser Power to 30%.
(4) Set Fill Interval
As we have already known, Fill Interval is the distance between the dots constituting the engraved pattern. If the Fill Interval is too large, the engraved pattern will be light-colored and might lose some details; if too small, the dots will overlap, making the engraving color too dark and the pattern indiscernib
We need to run tests to find the best fill interval. Engrave a series of squares with different dot intervals and record the interval with the clearest diagonal texture as the optimal interval.
Based on the tests, we set 0.14 mm as the Fill Interval.
Snapmaker Luban has preset values for some material, which are tested and recommended.
For more information about how to test and set work parameters, refer to the following articles:
(5) Generate the G-code file
After configuring the work parameters, save the toolpath settings and generate a G-code file in .nc format.
(6) Start laser engraving
Transfer the G-code file to the laser engraving and cutting machine. Put on laser safety goggles, and we are ready to go!
The methods on material selection, picture selection and editing, and laser engraving discussed herein are for reference only.
Snapmaker assumes no liability or responsibility for any property loss, personal injury, machine damage or expenses incurred by the methods on material selection, picture selection and editing, and laser engraving discussed herein or in any other means related to such methods.