Skip to Main Content

CNC Guide

A guide to using the Shopbot CNC machine in MAKE ll at Library 21c

Vectorizing Images

Tracing bitmaps is a way of converting a standard image file (e.g. JPGs, PNGs) into vector files by drawing a line along the border of any two pixels of different colors. In order to do this, select the "Import Bitmap for Tracing" button from the File Operations group or simply drag and drop the images into the workspace.

Next, select the "Trace Bitmap" icon in the "Create Vectors" group. You can trace either black & white images or full color ones. Black & white images are the easiest, as all the software has to do is draw lines around the black shapes. If you need to work with full color images, the software will first have to simplify the image by reducing it to no more than 16 different colors.

Black & White Images

For black & white images, the only option is threshold, which runs from 0.01 to 0.99. If your image is not pure black and white, but contains shades of gray, this is what will determine what shades are treated as black instead of white.

Color Images

The software will automatically simplify the image to be no more than 16 colors, and you can control this with the slider bar under Number of Colors / Threshold. After setting the number of colors, use the check boxes to select which colors will be in the new vector. You can also click directly on the image to select the color.

Other Options

  • Corner Fit: How sharp corners are kept when vectorizing. Looser corners may give an more accurate representation of how the material will be cut, especially with an exterior cut. Tighter corners may be more true to the original design.
  • Noise Filter: The higher the filter level, the more noise (random pixels that do not match the color of nearby areas) is ignored. Setting this to the right level can result in better vectors, but too high may result in areas merging.
  • Bitmap Fading: How faded the bitmap is in the preview area - more faded makes it easier to see the vector preview but harder to see the original bitmap. This has no impact on the final vector.
  • Group vectors: If the created vector is composed of multiple shapes, it will automatically group them.

Additionally, you can use the mouse to draw a bounding box within the selected bitmap and only the area within it will be vectorized. Once you have everything set, click preview to show the vector lines and if it is what you need, click Apply to create the actual vectors.

Multiple vectors can be created - after creating the first one, simply adjust any settings and selections and click Apply to create them.

If the trace is not working properly, try adjusting the slider bars to see if you get better results. Be aware that not every image can be traced well, and the more complex it is the more difficult it will be to get a satisfactory tracing. If you are unable to get a proper trace in VCarve, you may be able to get better results by taking the bitmap into a graphics design program such as Inkscape or GIMP and simplifying it before trying to trace it in VCarve.