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.