HDevelop User's Manual

2.3. MAIN WINDOW 27
in a graphics window. The third mode can be used whenever image data is displayed
overlaid with region data in a graphics window (the graphics window does not need to be
active for this). In this mode, you can click into any of the segmented regions, and the
histogram of the image within that region will be computed and shown. If you click into a
part of the image that is not contained in any of the overlaid regions, the histogram of the
entire image will be displayed. In the fourth mode, the same mechanism is used for regions
that have gray value information, e.g., image objects created by ÖÙ ÓÑÒ or
ÒÒÐ×. Here, the histogram of the image object you click into will be displayed.
Finally, when the graphics window the image was sent from is cleared, the histogram is
not reset.
When a multi-channel image, e.g., a RGB color image, is sent to the tool, by default the
histogram of the first channel is displayed. The combo box ÒÒÐ lets you select the
channel from which to compute the histogram.
The radio box in the upper center of the tool lets you select whether to display the histogram
with relative or absolute frequencies. When you select ÊÐ, the frequencies of
individual gray values are displayed as percentages; when you select ×, they are displayed
as the actual number of pixels having a particular gray value. See the operator
ÖÝ ×ØÓ in the HALCON Reference Manuals for details.
Sometimes it is desirable to suppress the updating of the histogram when new image
data is available, e.g., if you want to select thresholds for a gradient image, but want to
visualize the original image along with the segmentation (see below). To do so, you can
deselect the checkbox ÔØ.
The main part of the tool is the area, in which the histogram of the image is displayed
in blue. This area contains static parts and parts that can be interactively manipulated.
The first static part is the horizontal coordinate axis, which displays the gray values in the
image. For byte images, this range is always 0 . . . 255. For all other image types, e.g.,
real images, the horizontal axis runs from the minimum to the maximum gray value of
the image, and the labeling of the axis is changed accordingly. To the left of the display,
the vertical axis representing the frequency of the gray values is drawn in white. The
final static parts of the display are three cyan arrows. The two upward pointing arrows
denote the maximum and minimum grayvalue of the image. The downward pointing
arrow denotes the gray value that occurs most frequently, i.e., the peak of the histogram.
These data are displayed in textual form within the ËØØ Ø area of the display.
The dynamic parts of the histogram area are the three colored lines, which can be manipulated.
The dashed horizontal yellow line can be dragged vertically. The label on this line
indicates the frequency of gray values above this line. The vertical green and red lines
denote the minimum and maximum selected gray value of the histogram, respectively.
The selected range is drawn as a white bar below the horizontal gray value axis. The gray
values on which the two vertical lines lie are displayed next to the lines in the same color.
The frequency of the respective gray values is displayed within the ÝÒÑ Ø area
of the display.
The selected range of gray values can be used for two major purposes. First, when the
combo box ×ÔÐÝ is set to ÌÖ×ÓÐ, the image, from which the histogram was
computed, is segmented with a ØÖ×ÓÐ operation with the selected minimum and
maximum gray value. Depending on the setting of the combo box ËÒ, the segmentation
result is either displayed in the graphics window, from which the image was originally
sent (ËÒ = ), or in the active graphics window (ËÒ = ÌÓ ØÚ). Second, if
HALCON 6.0