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E-24 A-61122/A-61124 March 1999
Staircasing
Staircasing is displayed when a detail on the scanned image
switches from the scan line to the next line of the grid. This is the
same degradation seen on computer-generated images and is
most apparent on shallow slopes and soft curves. Staircasing can
be minimized by scanning at higher resolutions (more dpi).
One factor which can aggravate staircasing is skew. Unlike
computer-generated images, scanned horizontal and vertical
lines may not be square with the image. A slight skew when
feeding the original into the scanner can cause square lines in
the original to have a shallow slope on the scanned image, thus
introducing staircasing.
Aliasing
If the spacing of details in an original is close to the dpi of the
scanner, aliasing can occur. Aliasing causes a false image to
appear over the true image which is illustrated in Figures A and
B. Note the heavy diagonal bars over the narrow bars in Figure A
and the cross hatch patterns in Figure B. You can reduce this
problem by scanning at a much higher resolution or selecting the
Screen Removal option of the Image Enhancement filter.
Figure A Figure B
Figure A Bars at 10, 50, and 96 lines-per-inch, scanned at 200
dpi with Fine Line enhancement.
Figure B 120 dpi screen, scanned at 200 dpi with Fine Line
enhancement.
NOTE: 1 line-per-inch = 2 dots-per-inch
Shallow lines with staircasing