Raster and vector are two different object types, which require different modes of laser processing. Raster object types are comprised of pixels. For instance, a photograph on the computer is a raster file, in fact, most common image formats, JPG, BMP, GIF and PNG are all raster types. Vector graphics on the other hand are comprised of lines and splines. Unlike Raster, Vector files can usually be scaled to any size without loss of quality, this is because, each line and spline are mathematically formulated, giving you the perfect representation for any scale, whereas Raster, particularly with upscaling, will lose resolution and quality.
The laser’s approach to raster images and vector images is very different to one another.
Similar to an inkjet printer, where the file is printed line by line, raster engraving on a laser reproduces the greyscale representation of the job file, line by line. This is the standard process for engraving.
How does this work with a laser?
As mentioned above, a raster file is ultimately a bitmap or flat image file, made up of pixels. The image is engraved line by line, point by point, just as with an inkjet printer – instead rather than ink being applied, material is removed pixel by pixel by the laser.
The image is sent out to the laser in greyscale, each pixel is a variant of this greyscale, from black, which is 100% of the available power, determined in JobControl settings, through to white, which is no power. The engraver axis then moves at super high speeds delivering the laser power that represents the specific pixel thus resulting in an engraved image.
The speed of the two axis is very different for the line-by-line of the raster engraving. The speed is highest on the x axis (the axis the laser head is attached to) and lower by comparison on the y axis.
In raster engraving, the PPI parameter (PPI = pulses per inch) to be selected in the Trotec JobControl laser software is important, as this controls the density of the laser points (the resolution). You can read more about the parameter definition here.
Vector engraving, often referred to as scoring, involves the laser head moving around in a similar fashion to an illustrator drawing with a pencil. Rather than engraving the job line-by-line, pixel-by-pixel, the image is broken down into a series of lines and contours, where the engraving head traces around the shapes.
The easiest way to picture it is by drawing a circle on paper. If you were to draw a circle on paper in a ‘raster’ fashion, you will have a series of lifting and setting down your pen as you moved from line to line. Vector on the other hand, is a single pen-down motion, the circle is drawn in one movement.
Vector files consist of lines and curve geometry. In the graphics program, these lines are maked as hairlines which JobControl then identifies as vectors for vector engraving.
The difference between vector engraving and vector cutting is all in the power. If a lower power setting is chosen, the line is “scored” as engraving; higher power produces a vector cut that goes through the material.
See here for more on the quick determination of optimal laser parameters.