|Intelligent Scissors in GIMP
a previous article (Digital
Image Editing with GIMP), I
suggested that you could get most of the benefits of a $1000 image
editing program at zero cost by using the open-source GNU Image
Manipulation Program (GIMP). This program offers a vast array of
features, from the most basic editing tools, to some extremely
powerful techniques to achieve quite complex tasks.
have been using GIMP as my main image editor for several years,
mainly using simple features such as tools to crop photographs, or
change the brightness and contrast. But, as noted in the earlier
article (or simply hinted at) GIMP has a number of very powerful
tools. For example, suppose that we wanted to cut an object out of a
photograph for use as a stand-alone image. How would we go about
doing this? In Gimp, one answer is to use the “Intelligent
the name of the tool suggests, the “scissors” are used to cut out
part of an image, but this is accomplished with minimum effort on the
part of the user – hence the “intelligent” qualifier.
for example, that we want to extract the image of the bull from the
photograph shown below (left). Firstly, we open the original image
in Gimp. Now, since we are only interested in the portion of the
image containing the bull we can crop the image appropriately and
then enlarge the selected area. Click on the Rectangle Select Tool,
draw a box around the bull, select Image – Crop to Selection, then
View - Zoom – Fit Image in Window.
it’s time to click on the intelligent scissors’ tool. The cursor
changes to crosshairs with an adjacent tiny scissors icon. We
position the crosshairs along the bull’s back, immediately ahead of
the junction with the tail, and left-click on the mouse. A white dot
shows our first selected point. We move along the bull’s back,
selecting individual points as we go.
don’t have to be too precise as the scissors are intelligent so the
selected outline pretty well follows the desired contour. However,
sometimes it’s necessary to select an inflection point so as to
avoid the selected contour from taking a short cut away from the
desired outline of the object. Note, for example, in the above
screenshot (right) that the selection follows the bull’s contour,
even when we select two points that are quite far apart. However, if
we are too ambitious, i.e. going from the back of the neck to the tip
of a horn, the selected line fails to follow the contour of the neck
and jumps across to a point near the base of the horn.
are “tricks” to make our lives easier in such situations. Edit –
Undo Modify Scissors Curve (Ctrl-Z is even easier!) will remove the
selected point at the tip of the horns. We can then select a couple
of points along the neck to the base of the horns before continuing
to define the horns themselves. It is also useful to temporarily
enlarge our view in areas where the image has considerable detail
(e.g. the horns and tail). Selecting View – Zoom In (or just using
the + key), and re-centering the image in the window using the
scroll bars, enlarges a section of the image and makes point
selection more definite.
all the desired points on the outline have been selected, we can
click on the very first point in order to complete the selection.
Hovering the mouse over this point produces a message on the status
bar indicating "Click to close the curve". Having done
this, the status bar message indicates "Click or press Enter to
convert to a selection". Clicking once more on the image
changes the solid line with the selected points into a continuous
dashed line that "shimmers" to highlight the selected area.
Now, we can copy the selected image to the clipboard using Edit –
we can create a blank canvas on which to store our extracted image.
Select File – New and choose an appropriate width and height. In
my case, the image of the bull would fit into a frame of 2500 x 1400
px. Clicking OK displays the new blank image window onto which we
can copy the extracted image of our bull using Edit – Paste. Save
the new image as a new JPG file. Job done!
that the final product isn't perfect. (For example, do you see the
grey area in the lower portion of the end of the tail?) I could have
spent more time refining the final image but, for me, the end result
is good enough for government work! And, actually, I think it's an
amazing result for a few minutes work with a free image editing
Image Manipulation Program (GIMP) (Open Source)
Kimball, Peter Mattis and the GIMP Development Team
published: January 2019
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