Scanlab RTC 4, Installation And Operation Manual

Page: 47 / 136

RTC
®
4 PC Interface Board
Rev. 1.3 e
5 Advanced Programming
47
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5.7 Scanning Raster Images (Bitmaps)
The vector commands described in chapter 4.2 are
intended for scanning vector based images. However,
the RTC
®
4 also allows reproduction of raster images
(or bitmaps). That means black-and-white images
and even greyscale images can be created with a
suitably prepared laser. Furthermore, raster and
vector based images can be combined as desired.
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 (set position) moves from one pixel to the
next at a constant time rate. The pixel distance and
the output period can be set by the user.
Each pixel is usually marked by one laser pulse. For
black-and-white images the laser will be turned on or
off at each pixel. Greyscale images can be created by
modulating the laser power or the pulse width of the
laser pulse for each individual pixel or, alternatively,
by varying the number of laser pulses per pixel.
Please refer to the section
"Laser Control" on page 50
for details.
Software Commands
Before starting an image line, a jump command to
the start position of the line must be performed.
The image line itself starts with the command
set_pixel_line (see page 113) . This command turns
on the pixel output mode, sets the pixel output
period T and defines the distance in the X and
Y directions (dx, dy) between two adjacent pixels in
the line.
Pixel Output
Each pixel in the image line is then created by one
set_pixel command. This command defines the
pulse width of the LASERON signal for the pixel.
In addition, an analog output signal (ANALOG OUT2,
10-bit resolution) can be specified for each pixel.
The analog signal is transmitted synchronously with
the pixel output (scanner position) and can be used
for modulating the laser power. (See the section
"Laser Control" on page 50 .)
Data Input (Optional)
If the RTC
®
4 is used together with an optional I/O
Extension Board, the command set_pixel also allows
data to be read from an analog input port
synchronous to pixel output. The input data is
written to the RTC
®
4 list buffer, from where it can
later be read. For further details please refer to the
commands
set_pixel (page 112) and read_pixel_ad
(page 100) .
Notes
• The commands set_pixel_line and set_pixel are list
commands, i.e. they are written into a list.
• The command set_pixel_line requires two list entries in
the list buffer memory.
• The number of pixels in an image line is limited only by
the capacity of the RTC
®
4 list buffer (see page 130 ). It
is suggested – especially for large bitmaps – to set up a
new list for each image line to avoid a list change during
the execution of one line.
• Each image line must start with a set_pixel_line
command.
• The set_pixel commands for the individual pixels must
follow immediately after the set_pixel_line command.
The first subsequent command in the list which is not a
set_pixel command turns off the pixel output mode.
• The pixel distance (dx, dy) in the X and Y directions
(in bits) can be specified with floating point numbers.
This allows scaling and rotating the image without
rounding errors. However, the actual output
coordinates (in bits) of each individual pixel are always
rounded to integer values.
• The pixel output period can be any multiple of 10
µ
s,
whereas the standard output period for the microsteps
in the vector mode is always 10
µ
s. Also see the section
"Scanner Control", page 49 .