Oce 3050 - Page 46

46 Océ 3050 User Manual
THRESHOLDING The thresholding setup screen is the most important of the
"Imaging Scanner Setup" screen, allowing separate adjustment of the track
area, tracking limits and thresholding levels together with half tone and
polarity settings. Together, these determine how "Image Processing" analyses
the image density data it obtains during the scan and uses this to threshold the
incoming data. The output of the thresholding operation is preserved as
greyscale information representing the difference between the data signal level
and the computed threshold value and it is used for further extraction
processing which is described below.
THRESHOLDING / TRACKING LIMITS This control has two sliders MAX and
MIN which set the maximum and minimum limits, which together define the
range of film density within which the automatic tracking system of "Image
Processing" is allowed to work. For automatic batch operation these limits will
need to be very wide, so that image data can be retrieved from frames having
widely varying background densities and frames which have variations of
background density within the same image.
An inherent consequence of tracking the background density is that there is no
means of distinguishing a large area of intentional foreground, such as a logo
block or inverse image area, from a real change in background density. In order
to make such a distinction, it is necessary to use other information, such as the
absolute density value, to identify the feature as foreground data. The
TRACKING LIMITS settings allow this to be done by defining a limit to the
dynamic range of the tracking system. Reducing the MAX limit will prevent
the tracking system from eliminating the centres of intentional solid areas.
Conversely, raising the MIN limit will prevent the tracking system from trying
to detect changes in the background when it is really required that they are
suppressed. A typical use of this would be to suppress the detection of changes
in background as the scan crosses from one sheet to another sheet on a
multipage image.
It is anticipated that adjustment of the tracking limits will be used in a second
pass on specific (and normally a very small percentage) of images which have
this type of feature. This second scan would be an optional choice for the
customer since the information content is still present on the first scan. What
is being provided is a means of improving the appearance of the image rather
than detecting extra information.