cen as a starting
the illumination
nsity explicitly
1 the case of er-
lues and to the
s of the signals
f a white signal,
spectre and the
be determined.
lon intensity is
; procedure, the
und the optimal
the illumination
eference values
ent illumination
jne illumination
réseau illumina-
s are visible in
ensor and it is
tion of the sen-
mage. The light
he ellipse to be
e of the signals
nated. For this
background are
or the measure-
surement of the
value is chosen
ind grey values
regulated on a
neasurement of
lack signal tar-
t contrast of the
ckground.
cur in the retro
kground. There-
' to differentiate
| be used. From
nade within the
rosses, one for
ages, signal tar-
means that the
hese signals are
For this reason,
always effected
rpose is to give
om 0-50 and to
s, bright interfe-
ferences are re-
' image are then
(n be found and
, effected for the
w the threshold
lues above this
on the different
‘negative attributes, the threshold values, for isolating
the crosses and for isolating the ellipses, are also
adopted to the brightness conditions in the basic
image. The grey values of the original signal and the
background grey values are taken as a reference for
this reglementation. For the threshold value of the
réseau crosses, the value of the background is used
and increased by 2096 of the difference between back-
ground value and the grey spectre value of the réseau
crosses. For the ellipses, the brightness value is in-
creased by 90% of the difference to the background
and is used as a reference value. The true regulation is
then effected in small steps as for the adjustment of the
light intensity of images without réseau preillumina-
tion. Should the threshold value be lower than the cal-
culated reference value, the threshold value is incre-
mented, otherwise decremented.
A prerequisite for the described adaptation of the
illumination intensity and the threshold value is the
even movement of the sensor over the image. It is im-
possible, to adapt the illumination intensity to the
illumination differences on the negative when subse-
quent measurements are effected in totally different
parts of the negative. A second advantage can be seen
in the fact that the movements of the sensor are de-
creased and possible delays before sensor positioning
can be avoided. This results in the necessity to assure
the scanner movement to the closest point and a gra-
dual changement of the brightness. The adaptation of
illumination intensities and of the threshold values can
then be effected. This rearrangement of the points
happens in a step taken before measurement.
USER INTERFACES
The development of a complex user interface was
avoided in order to make possible a later introduction
of specific customer demands. The experienced user is
able to create his own measurement programs, adapted
to his own demands.
For standard applications, on the one hand, given in-
terpreter files can be used, on the other hand, program
generators can be applied which are independent from
the MIROS measurement system. The command
structure and the interpretation of such an interpreter
file are similar to the batch programming in a DOS
shell in order to guarantee an easy approach in the
possibilities of the interpreter. To give an overview of
the work of the interpreter, some of the implemented
commands are described in the following:
l. Include
allows to import command sequences to the actual
program position. With this command, standard
command sequences can be combined as a macro
and be included.
2. Label
define positions in the measurement program to
which jumps with the commands "Goto" and "If"
are possible.
3. If
makes possible to effect a conditional jump. The
functions ’Yes-Pressed’ and 'No-Pressed' have
been implemented which react to a Yes or No of
the user. Further functions can be implemented.
4. System
executes a DOS command which is given as a pa-
rameter or starts a DOS shell. This shell can be left
with the "EXIT" command.
5. Getpicture
Starts the image orientation. Image numbers,
réseau types and as an option also the information
which side of the negative is on top are required.
6. Automode
sets the level of automation. One can chose be-
tween 'ON', 'OFF' and 'HALF'. With the 'ON'
parameter a fully automatic measurement is cho-
sen. With the 'OFF' command a manual measure-
ment is set. The 'HALF' command activates this
manual measurement after the automatic measure-
ment has failed (major signal disturbances).
7. Meas
is the command that starts the actual measurement.
As parameter amongst others, the file from which
the points to be measured are taken, is disposed. In
this file start and end lines can be named.
RECOGNITION OF MARKS
Measurement of Ellipses
Circular point signals are fixed as target marks on the
object. This assures a conform copy in the image. The
measurement of positions in the negative is thus re-
stricted to the measurement of ellipses, as circular sig-
nals are always reflected as ellipses, because of the
perspective image. As a point coordinate in the image
the center of this ellipsis is determined. The problem to
be solved is a interference tolerant identification of the
margin points of this ellipsis.
Problems that might occur are the following:
o Is the approximate value, which is the starting
point for setting the margin points, within or with-
out the ellipsis?
e How can this approximate value be improved with
a fast and safe algorithm?
e How distinctive are the margins of the ellipsis, are
all margins homogeneous, how can the margins be
recognised by avoiding errors?
e Are all recognised margin points part of the ellip-
sis, or do they just represent areas of high grey
scale differences?
< Is the recognised object a measurement target, or
just a disturbance on the negative, in the shape of
