Number of points in a horizontal Line Roi different when line width > 1

[Cardone, Giovanni]

Hi,

I discovered that when tracing an horizontal line on an image and retrieving 
the profile intensity, the number of points is artificially increased by one 
when setting a line width larger than one.
Here is a python script that reproduces the issue

from ij import IJ

from ij.gui import Line

imp = IJ.openImage("http://imagej.net/images/Cell_Colony.jpg";)

imp.show()

h = imp.getHeight()

w = imp.getWidth()

for line_thickness in (1, 5):

    roi = Line(0,int(h/2),w,int(h/2))

    roi.setLineWidth(line_thickness)

    imp.setRoi(roi)

    y = roi.getPixels()

    print("Line thickness: %d - Number of points on the X axis: 
%d"%(line_thickness,len(y)))

This inconsistency only happens when the line is perfectly horizontal. I looked 
at the code and it seems that the extra point at the end of the profile is 
generated by the function PolygonRoi.fitSplineForStraightening() called by 
Straightener.straightenLine().
In my tests I could see this happening only when the Line Roi is horizontal, 
and it affects also a profile plot (e.g. when calling IJ.run(imp, "Plot 
Profile", "")).

In my script I was able to bypass the issue by using instead a rectangular Roi 
with height equal to the line thickness, but I thought it was important to be 
aware of this anomaly.

Best,
Giovanni

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html