Lines, Arrow, Text Tool

This tool lets you draw straight or curved lines with optional arrowheads at either end on an image. The width, color, and transparency of the lines are controllable and there are several arrowhead styles available as well. Lines are automatically anti-aliased to avoid jagged edges. Optionally, you can place a text box at the start of the line or arrow. This is useful when using the tool to annotate photographs.

You cannot draw in color over a black and white image without first converting it to a color image by running the image through the Convert transformation.

The controls listed below change the characteristics of the current line. If there is more than one line, you can select the one you want to operate on by clicking any of its control points. Lines are defined by positioning control points. A simple straight line has two control points – one at each end. To make more complicated shapes, you can add more control points – the line always passes exactly through each one in sequence.

Broken lines are created by connecting control points with straight line segments. Curved lines are created by connecting the control points with cubic spline segments whose shape you can control with two additional handles per control point (see below).

Amount

The amount control lets you scale back the overall transparency or you can create a mask to restrict lines and arrows to specific parts of the image.

Line Width

This slider controls the line width in pixels. The smaller the width, the finer the line. Arrow heads, if any, scale up or down proportional to the line width. You can also adjust the line width using the mouse scroll wheel.

Arrowhead size

This slider controls the size of the arrowhead relative to the line width.

Transparency

This slider controls the transparency of the line and arrowheads. The more transparent, the more the image shows through.

Line Type

This control lets you select whether you want to connect control points with a broken line or with a spline curve.

Arrowheads

This control lets you select whether you want arrowheads at the beginning or end of the line, neither, or both.

Arrow Head Type

This control lets you select Normal, Sharp, or Blunt arrowheads.

Snap to 45 Degree Increments

When this button is depressed, when dragging control points (and there is more than one), they are limited to forming horizontal, vertical or 45 degree lines, whichever is closest to the direction in which you are dragging. This makes it easy to create exactly horizontal, vertical or 45 degree lines or line segments.

Text Box

When this button is depressed, a text control pops up to let you place a text box aligned with the starting point of the line (or arrow). If you close the text control and need to re-open it, just click the Text Box button twice. If the Text Box button is not depressed, no text box is placed over the image.

Color

This control sets the line color.

Editing lines and control points

Control points are displayed as an overlay on the input image. You can add or modify control points or lines as follows:

Creating simple lines

Clicking on the input image near an existing control point selects the line of which the control point is a part. You can also drag existing control points to reposition them.

Clicking on the input image away from any of the existing control points starts a new line. The first click defines the beginning of the line and the next defines the end. If all you want to do is create a few simple line segments, this is all you need.

Editing control points

To add control points to an existing line, first click on one of its control points to make sure the right line is selected. Next, shift-click to insert a new control point. If the closest thing to the cursor when you insert the new control point is a line segment, the control point is inserted in the middle of that line segment. If closest thing is one of the endpoints, the control point is inserted at the beginning or end.

To reposition a control point, drag it to the desired location.

To remove a control point, ctrl-click on it.

Depending on the Line Type (see above), either a broken line or a spline curve is run through the control points and a rough outline is displayed as an overlay over the input image.

If you select a curved line, each control point has two additional handles which control the incoming and outgoing slope and velocity of the curve at that point. The slope controls the angle at which the curve arrives at or departs from the control point. The length sets the velocity which controls how fast it arrives or departs – the higher the velocity, the further the curve goes before turning toward the other end of the segment. If you select a large enough velocity and the control points are close enough to each other, the curve may kink or intersect itself.

Removing entire lines

To remove an entire line, remove one control point at a time until there are none left.

  Using Text Boxes

Text boxes are placed at the starting point of a line or arrow. To add a text box, depress the Text button which then pops up a text control. If you want a text box without a line or arrow, create just the starting point of the line. To place text in the margins of an image, first use the Add Border transformation to create a border around the image. If you close the text control and want to get it back later so you can check the settings or make some modifications, click the Text button twice.

Enter the desired text into the Text field and then set the Font, Font Size, and other settings as necessary. To get the effect show above, Background Transparency was set to 0%, Alignment was set to Lower Right to connect the arrow to the lower right corner of the text box, and Text Margins was increased to cover the gap between the start of the line and the text box.

Another possible annotation style is:

In this case, the arrow Color and the Outline color are both set to red.