RTC
®
5 PC Interface Board
Rev. 1.9 e
8 Advanced Functions for Scan Head and Laser Control
192
8.8 Scanning Raster Images (Bitmaps)
The vector commands described in chapter 7.1 are
intended for scanning vector based images. However,
the RTC
®
5 also allows reproduction of raster images
(or bitmaps). That means black-and-white images or
greyscale images can be created with a suitably
prepared laser. Furthermore, raster and vector based
images can be combined as desired.
8.8.1 Principle Of Operation
A raster image is created line by line, where each line
consists of a number of equidistant pixels. A line is
reproduced in a single scan. During this scan, the
laser focus moves – as with a normal mark command
– at an approximately constant velocity along the
entire image line (the motion is microvectorized). The
individual pixels will be marked in passing: each pixel
receives a laser pulse at the appropriate location. By
varying the laser energy from pixel to pixel, greyscale
images are produces (black-and-white images are
also possible as a special case). For controlling the
laser, pulse lengths (digital) and voltage levels
(analog) are outputted.
Notes
• You can combine pixel output mode with
Processing-on-the-fly (see page 177), but not
with Wobbel (see page 167).
8.8.2 Software Commands
Before starting an image line, you should execute a
jump command to the line’s start position.
At the beginning of each image line, the pixel output
mode is activated with the command set_pixel_line
or set_pixel_line_3d. The pixel distance and pixel
output period (and, resultingly, the speed at which
the image line is traversed) are simultaneously set as
well. The pixel output period is defined via the
parameter
HalfPeriod
(half pixel output period).
This is also half the laser period. The pixel distance
between two adjacent pixels in the line – and thus
also the marking direction – is defined via a 2D vector
(
dX
,
dY
) by set_pixel_line or (for pixel marking on
sloped surfaces) via a 3D vector (
dX
,
dY
,
dZ
) using
set_pixel_line_3d. The
set_pixel_line/set_pixel_line_3d commands are also
used to define which of the two analog ports
(ANALOG OUT1 or ANALOG OUT2) should output the
analog voltage levels of subsequent set_pixel or
set_n_pixel commands.
Directly after the set_pixel_line/set_pixel_line_3d
command, set_pixel has to be called separately for
each of the line’s image elements. This defines the
laser energies to be discharged at the corresponding
pixel locations: a pulse duration and/or a 12-bit
analog voltage level can be specified (see "Laser
Control" on page 193). Pixel pulses are outputted at
the LASER1 port, analog voltage levels at either the
ANALOG OUT1 or ANALOG OUT2 analog port (see
above).
To specify an identical analog voltage level or pulse
duration for multiple (
n
) directly successive image
elements in an image line, you can use the
set_n_pixel command instead of (
n
) set_pixel
commands. Then only one command will be stored
on the board, but the list will execute an appropriate
set_pixel command
n
times. Particularly for black &
white images, this can drastically reduce the size of
lists. Don’t confuse set_n_pixel with the n_set_pixel
command (multi-board version of the set_pixel
command).
Prior to the end of an image line, no command other
than set_pixel or set_n_pixel must be written into
the list. After set_pixel_line/set_pixel_line_3d, the
first list command that is not a set_pixel or
set_n_pixel command stops the pixel output mode
and thus processing of the image line. Each
set_pixel/set_n_pixel command that does not follow
another set_pixel/set_n_pixel or
set_pixel_line/set_pixel_line_3d command will be
ignored during processing and will thus be a short list
command (see page 217).
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