Using ``scissors'' to manually select objects or groups of objects

Any object or combination of objects can also be selected manually. Click on the desired image and select ``Image..Manually select area'', or press F3. Click OK on the message box, and outline the desired objects as described below.

As with any other selected region, clicking anywhere outside the region, or reconfiguring or moving the image window will deselect the area. The selected area(s) can be grabbed and copied or moved (depending on the position of the main ``Move'' button) as a group by positioning the mouse over the crawling dots and clicking the 1st mouse button.

The method of selecting the outline can be changed in the `Config..' dialog. The options are:

Single (freehand) - Only one object can be selected. Click the left mouse button and draw an outline around the object. When you unclick the mouse button, a message box appears instructing you to click somewhere in the object to define its inside. After you click, the inside will turn blue for a moment, and then its outline will be replaced by crawling lines, indicating the outline of the selected area.

Multiple (freehand) - An arbitrary number of disjoint areas can be selected. Draw a freehand outline around the object with the mouse as before. When you unclick the mouse button, a message box appears instructing you to click somewhere in the object to define its inside. After you click, the inside will turn blue. Continue selecting new objects in the same way. When finished selecting objects, click the main Cancel button. The blue will disappear and be replaced by crawling lines around each of the areas. Even though they are disjoint areas, they will be acted upon as a unit. For example, if you click the mouse on the edge of one object, all the objects will be copied at once.

Polygon - Click with the left mouse button at various points around the outside of the object to define a polygon around the boundary of the object. After each click, a small box indicating the control point will appear. These boxes can be repositioned at any time by dragging them to a new location. When finished, press the space bar (or any other key). A message box will appear instructing you to click somewhere on the object to define the inside. Note: a minimum of 3 control points is necessary to define the polygon.

Point-to-point - Click with the left mouse button at various points. Press space bar or click right mouse button when finished. A polygon is drawn in a manner similar to the drawing mode in xfig.

Once a non-rectangular area has been selected, it can be reactivated at any time with the `reselectarea' menu option, without the necessity of re-tracing the previous outline.

One limitation not shared with rectangular selected regions is that the entire irregularly-shaped region must lie within a single image or on the background.

Interaction of painting with non-rectangular selections.

Like rectangular selections, non-rectangular selections also interact with painting and gradient fills. In the above example, the black area around the fractal was selected by double-clicking on the black region. When ``Draw..paint region'' was used to change a small rectangular portion of it to red, only the selected region was affected. Normally, if no non-rectangular region had been selected, the entire square would be filled with red. If the fractal itself had been selected (by double clicking on the fractal, or by clicking on the black and selecting ``Switch selected/unselected''), only the fractal part would be painted red.

Here are some tips on selecting objects in an image:

• If the object is near the edge of the image, it may be helpful to put a border around the image.
• If the correct area is not completely identified, try double-clicking on a slightly different point.
• If the object is ill-defined or touches other objects of a similar color, it may be necessary to draw an outline around the object to separate it. This can be done by the ``spray math'' function which can lighten or darken small regions, or by drawing on the image with the ``sketch'' function.
• The sensitivity for small variations in color can be adjusted in the ``Config..Configure..Object threshold'' menu. This value is the percent difference in each color required to separate objects. A higher value results in larger areas being selected. If difficulty is experienced selecting the correct area, try adjusting the Object Threshold value to match the color of the desired area.
• On slower computers, object identification may take several seconds if the image is large. On really slow computers, if the system load becomes excessive after a complex area is selected, it can be reduced by increasing the SLOW_DELAY constant in xmtnimage.cc and recompiling.