Creating stimuli with Inkscape and other software

All things you can draw are objects. In the screenshot above, the are four objects (a rectangle, a circle, a triangle, and a text). Each object has a number of properties, such as a fill color, and a border (i.e., stroke) color. You can change the features interactively.

There are a number of reasons for the preferred use of bitmaps in PsyToolkit. For one, bitmaps will look the same on any computer, whereas stimuli that are only described by the software are potentially rendered differently on different computers. Also, rendering bitmaps is computationally simplest and fastest, which matters because PsyToolkit aims to be fast.

You should see something like what you see in the image below. The orange window border is specific to my system and this might look differently on your computer, depending on what operating system you use.

For this lesson, I have made the Inkscape window as small as possible. This is just to make the images fit within the browser window. When you start it on your own computer, you will see much more information on screen. Especially, there are more tools than you see here.

Note: You see many symbols that all reflect Inkscape functions. At the center, you see the area where you can "draw" objects. This area is called the canvas. You see the shape of the page, just like you might do in a text processor. This layout is similar to other software. The best way is just to "play around" a bit to get a bit of a feel for the program.

The rectangle tool is indicated by the red arrow below. You can select the rectangle tool in different ways. You can click the rectangle in the toolbar on the left. Or you can type the key "r" or alternatively "F4".

You can do this in different ways. First of all, make sure the rectangle is selected. You need to click it, but before you click it, make sure you have selected the selection tool. You can do this by clicking the "arrow" in the toolbox on the left, or by typing the key "F1".

At the bottom of the screen, you see a palette of different colors. Select green. You will now see that the rectangle is filled green.

You likely will see that the rectangle still has a thin black border. This is called the stroke. You can either remove the stroke or make it green as well. To make it green, click a color from the palette, but while doing so hold the shift key. Alternatively, you can hold the shift key and click the little red X on the palette, which will remove the stroke color altogether.

Explanation of numbers in image below[] . Click the red X while holding the shift button. Make sure you do this while the green rectangle is selected (which you have if you see the black arrows around the object). .Click this symbol to export the selection as PNG bitmap.

You can resize the rectangle a bit to suit your needs. Just use the handles of the object. If you do not see handles, select the arrow selection tool (or type F1) and click the rectangle. Resize as you like.

From the menu, select the export option (menubar: File, Export Bitmap). You can also type shift+control+e to do this. Set the width and height. Or just set the width, and type "enter", and you will see that the height will be changed to keep the same aspect ratio. Select a filename and save it somewhere. Later, PsyToolkit can use this file for the experiment.

Explanation of numbers in image below: . First, make sure you export the selected object. . Make sure you select px (pixels) as the unit to work with. . Set the appropriate bitmap size. Inkscape will remember the values. Also, if you just want to change width and height, you only need to change width or height, and then press enter. Inkscape will appropriately adjust the value you did not change to keep the aspect ratio. . Select a filename. Make sure you have selected the appropriate folder/directory. . When everything is set, click "export" to save the selection as bitmap.

From the menubar, select "File", "save" and save the file. This is different from exporting as bitmap. This time, you save the whole page, not just the green rectangle. Next time, when you want to work on your stimuli, for example to make a change to the color or the size, you would re-open this file, make some changes, and again save the stimulus using the export bitmap function.

Summary: You have created a SVG file containing a green rectangle. You have selected the green rectangle and exported it as a bitmap. Altogether, you have two files of two different formats (one is SVG and one is PNG).

You first select the text tool [1], then you click the canvas and start writing [2], and further, you can change the font type, size, and properties [3].

You click the arrow symbol (or press the F1 key) and then click the text. It will be selected, as you see in the example below. Then choose a color from the palette. Because we are going to have a black background, you should choose a light color. If you choose white, you will not be able to see the text, though (but see the tip below on how to deal with that).

Click the rectangle tool (or press "r") and draw a rectangle. Make it black (you should know how to to do this by now).

Now click the selection tool (the arrow, or press the F1 key). Click on the text such that it is selected. Now click the "raise to top" button [1], or simply type the home key. This makes sure that the text is in front of the black background (see section on object order below for more explanation).

Now select the selection tool (or press F1) and select all objects. There are only two objects. Just bring the mouse cursor to a position of the top left of the canvas, hold the mouse button, and draw an box around all objects and release the mouse button. Now all object are selected. Alternatively, you can choose "select all objects" from the menubar (File, Edit, Select All, or just press control+a).

Now we are going to align the selected objects. First, press shift+control+a to activate the alignment dialog (see example below on the right). Click the center horizontally [1] and the center vertically [2] buttons and see what happens.

Now your stimulus is ready. Export this as a bitmap, and make sure it is not bigger than 800x600. If it is bigger, it will not fit on screen! Do not forget to save the file as well, just in case you want to change your stimulus later. Again, you will have at least two files. One is the SVG file and one is the bitmap file of the stimulus only.

Summary: In this example, you have learned how to write a text and put it on a background.

Select the "stars and polygons tool" [1] (or press the key *) and draw a triangle. Make sure, you choose the "regular polygon" [2] with three corners [3]. After you have clicked the "stars and polygons" tool button, move the mouse to the canvas. You will see that the mouse cursor looks like a little star. Click and hold the left mouse button and move the mouse and you will now see a triangle. The triangle has one "handle" [4]. You can use this handle to change the size and orientation of the triangle.

There are different ways to resize the triangle. One way is to keep the polygon tool selected and drag the one handle of the triangle tool. Alternatively, you can press F1 (or click the arrow tool, that is, the selection tool). You can now drag one of the 8 black arrows [1] (see below).

You can press F1 and resize or rotate. Press F1 (or select the selection tool) and click the triangle. Click once more and notice that the 8 black arrows around the triangle look differently! The type of arrows determines whether you can resize or rotate. Below, the black arrows are in rotate and skew mode.

Press shift+control+f (or select the fill and stroke button from the horizontal toolbar, or go to the menu bar, select "Object", "Fill and Stroke"). In the fill and stroke dialog, click "Stroke paint" and "Wheel" and choose a color. Below, you see that I choose red.

In the fill and stroke dialog, now click "Stroke style", and set the width to 10 and the unit to "px" (which it is by default). When done, click the close button of the fill and stroke dialog.

Select the triangle (press F1 and click the triangle). Now press "*" or select the "polygon and stars" tool of the toolbar. Now change "Rounded" from 0 to 0.140.

Summary: With Inkscape, it is easy to draw and modify shapes. With a few lines more, you already can have a little figure that can make your experiment a little bit more attractive to participants!

Press shift+control+d to change the document properties. Change the background color to black. Make sure you set the opacity to the maximum (in the image below, the opacity, or A, is set to the maximum value 255). The image below shows how to select the background color.

Draw a rectangle as shown below. Select the color white from the palette. Notice that Inkscape adjusts the arrows of the object (they are now white, and thus visible on the black canvas).

Select the rectangle and press control+d. This duplicates the object. Although you just see one object, there are actually two, but they are perfectly aligned on top of each other. Just click the only rectangle you seen and move it to the right. You will now see two rectangles.

Select the right rectangle and press F1 (or click the arrow in the toolbar). Now click the rotate-clockwise [1] symbol and notice that your rectangle is rotated 90 degrees.

Now activate the align and distribute dialog (menubar: Object, Align and distribute; or press shift+control+a). Select both rectangles (for example, by pressing control+a or by dragging a box around them). Now center the two object vertically and horizontally (as you have done before).

In fact, you could stop now and export the objects. But you can also go one step further. You can combine the two objects into one by "unifying" them. From the menubar select Path, Union. This is handy, because Inkscape now treats this as one object. If you want to color it, you just give it one color (instead of having to color two objects).

Objects can cover each other. If one object is covered by another object, you can "raise" it to the foreground. Select an object and press the "home" key to raise it to the foreground. Press then "end" key to do the opposite, to bring it to the bottom of the object stack.

Each object in Inkscape has multiple properties. Fill and stroke are two important properties. Fill color is the main color, and stroke color is the color of the border around it. If one of these is not set, it will just be invisible. If you want to draw a rectangle, you might not want a filling. If you click shift+control+f (which also has a symbol on the horizontal toolbar underneath the menubar), you get a dialog window in which you can set the fill and stroke properties.

Color in Inkscape is easy to select. You can just select a color from the palette at the bottom of the screen. But there is more to it. Each color has four constituents:

Each of these constituents is important. If you set Alpha to zero, the object will be invisible. Typically, you should set Alpha to its maximum value. If you want white, set all values to the maximum. If you want to know more about the so-called RGBA color model, check this: RGBA color space.

In Inkscape, you can very easily set these values. There are multiple ways to do this. For example, Inkscape lists RGB, HSL, CMYK, Wheel, and CMS models. They are just different ways to set colors. Which one you want to use depends on you. The "Wheel" method is very intuitive, just play around with it. Click anywhere on the color triangle and see what happens.