Using Inkscape for Biological Illustration A Guide for Entomologists, Taxonomists, and Other “On the Cheap” Illustrators

Zelia L ‘Kai’ Burington keroplatus (at)

Version 1.0 May, 2017


1. Introduction The purpose of this book When I was first starting out with insect illustration during my master's degree, I did everything by hand. I learned first by drawing freehand. Despite my best efforts, these drawings weren't particularly good. My thesis adviser showed me how to use a gridicule eyepiece and grid paper to produce better drawings. My drawings improved, but I could never get the lines just right. The illustrations were good enough for publication but still dissatisfying. Enter Inkscape. Several years ago I started using this software to produce illustrations for my dissertation. I had previously considered learning Adobe Illustrator, but the price deterred me. Now Illustrator is available only by subscription plan, making it an even less attractive option. Inkscape is free. I went looking for Inkscape tutorials dealing with biological illustration, but there were none. Some enterprising people had been using the software to produce other sorts of figures for publications, but no one that I could see was using it to produce the sort of line illustrations common to the biological literature. I struggled with the program and eventually arrived at an amateurish level of skill. This resulted in a short blog post about my methods ( Still, I wasn't satisfied. It has taken until now that I feel competent enough as an Inkscape user to produce nice publication-quality illustrations of which I am proud. This book is inspired by Dr. Ralph Hozenthal's "Adobe Illustrator: A Tutorial for Entomologists". I wanted to write something similar, a standard method for using Inkscape to illustrate insects and other biological subjects. I hope this book will be useful for other "cheap" entomologists, biologists, ecologists, taxonomists, graduate students, non-professionals, and anyone looking to make vectorized line art of organisms without a large monetary investment. About Inkscape Inkscape is an open source vector image program. Vector images are composed of line equations rather than of individual pixels like that of typical digital "bitmap" or "raster" images. While a raster image will become distorted and pixelated when enlarged, a vector image is infinitely scalable, and therefore never subject to scale-based distortion. Vector-based images are extremely "clean" in look and feel, and thus highly desirable for use in publications. To be open source means to be created by a community of unpaid enthusiasts. Anyone can look at the software code and modify it as they please. It also means Inkscape is permanently free of charge to use. Inkscape is still in development, but the tools currently available are powerful and sufficient for most biological illustration needs and are better every year. There are still


many things Adobe Illustrator does better than Inkscape, but likewise, there are functions that are included in Inkscape that are not easily available in Illustrator (see Chapter 10). In cases where Inkscape is behind, such as in the creation and use of custom brushes, there are often easy and only slightly tedious work arounds. The program is available for download in MacOS, Windows, and Linux formats from Other useful manuals and guides There is a wealth of tutorials on the Internet about using Inkscape. A good starting point for these is the Inkscape organizational website ( One of the best resources is "Inkscape: Guide to a Vector Image Program" by Tavmjong Bah. I highly recommend reading their book and trying some of the numerous tutorials before attempting the illustration techniques below. How this book is organized I have written this book to follow my method for making a scientific line drawing of insect genitalia. Each section covers a major step in completing the drawing. For best results, start with Chapter 2 and work through in a linear fashion. Several chapters (”Setae and Hairs”, “Shading”) cover specialized issues, while the rest are common to all sorts of line drawings.


2. Getting set up One of the most difficult parts of learning a new piece of software is finding ones way around the interface. If you are new to Inkscape, start here. If you are somewhat familiar with the program, at least read the sections on setting a template and preferences. The main tools When you first open Inkscape you will see a window similar to that of Figure 1.

Figure 1. The Inkscape Main Window.

At the very top of the window are the typical File, Edit, and other dropdown menus. Below this is the toolbar, which will have options related to the currently selected tool. On the left side bar are the main Inkscape tools. At the bottom of the screen are the color swathes, a Layers dropdown menu, information related to the currently selected tool, the current cursor position, and the current zoom level. On the right should be a toolbar related to saving and editing, and also a toolbar related to "snapping", which can be useful in positioning individual parts of an image. There may also be one or more


open "docks" on either side of the canvas. The tools most often used when illustrating biological subjects in Inkscape are: Selection Tool (F1) - For moving, rotating, and selecting objects and paths. The icon is a cursor arrow. Node Tool (F2) - For editing both the nodes and curves of vector objects and paths. The icon is a path. Zoom Tool (F3) - For zooming in and out of the canvas. Holding Shift changes the tool from zoom in to zoom out. The Icon is a magnifying glass. Bezier Tool (Default of Shift+F5): For creating continuous vector objects by placing nodes. The icon is a felt tipped pen and vector. Pencil Tool (F6) - For creating freehand paths where nodes are inferred from the shape of the path. The icon is a pencil. Tweak Tool (Shift+F2) - For changing the shape, width and direction of a path by "nudging" the boundaries. The icon is a wave. Other useful tools Some other tools that are less often used in this book and usually for specific tasks are: Rectangle Tool - For creating a white background behind the finished illustration. Circle Tool - For creating the annuli of hairs and other such structures. Calligraphy Tool - For creating a signature. Text Tool - For adding labels and text to figures. Keyboard shortcuts The keyboard shortcuts for the main tools are listed above. Several other key combinations are handy to know. Ctrl+C - Copies object. Ctrl+V - Paste copied or cut object at location of mouse cursor. Ctrl+X - Cuts object, removing it from the canvas and keeping a copy in memory for pasting. Ctrl+Z - Undo last action. Arguably the most useful shortcut. Ctrl+Alt+C - Stroke to path. Changes the vector stroke to a path with the shape and width of the original vector, bounded by a closed vector. This is a necessary step before using the Tweak Tool, and thus it is nice to know the shortcut. Ctrl+S - Save file. A wise illustrator does so often. Ctrl+A - Select all. Selects all visible objects and paths in current layer. Ctrl+G - Group. Groups paths and objects together as a single selection. This can be useful when aligning parts. External tools and peripherals


In addition to Inkscape, I also recommend using the GNU Image Manipulation Program (GIMP), another open source program. As Inkscape can only work in vectors, which do not lend themselves well to shading, it is often easier to shade in a raster program. GIMP, as Inkscape, has a large following and a large number of available tutorials. It is available here: While Inkscape can be operated with a mouse pad, it is recommended that a user at least use an external mouse to increase efficiency, decrease fatigue, and free up the left hand for using hotkeys. Ideally, one would use a tablet and stylus, as this most closely replicates the more natural act of drawing. Before using these, you should check the "Input Devices" options under the Edit menu and adjust them as you prefer. Working with Docks Most of the major option menus in Inkscape are in the form of movable dialogue menu interfaces called “docks”. They can either be opened in a separate window from the main workspace, or they can be “docked” or locked in position to the side or bottom of the workspace. Several of the most commonly used docks are listed below. Layers (Shift+Ctrl+L) - Used to create and alter layers of the illustration. Each layer can be selected individually, made visible or invisible, and locked to separate several sets of paths or objects on a single illustration. Fill and Stroke (Shift+Ctrl+F) - Used for altering the outline width and style of objects and paths, as well as the fill color or pattern. Undo History (Shift+Ctrl+H) - Allows tracking each individual action in an illustration’s history, and quickly revoking large numbers of actions at once. Align and Distribute (Shift+Ctrl+A) - Used to align objects and paths. Export .png image (Shift+Ctrl+E) - Used to export images from Inkscape.


Figure 2. The Inkscape main window with several docks open. These include Undo History, Fill and Stroke, and Layers.

By default, when a dock is opened, it will be locked to the upper right-hand corner of the workspace. Multiple docks can be opened at once, as in Figure 2. Each dock can be changed in position of the dock by left-clicking and dragging the title bar. The new position of the dock is shown with dotted lines. When working with Inkscape, I prefer the arrangement of Undo History, Layers, and Fill and Stroke docks as in Figure 2. Unless the preferences are set to save and restore dialogue status, Inkscape will not remember your dock setup and will leave dialogue menus closed upon starting the program again. Saving a template workspace When making a large number of similar drawings with the same system of layers and same page layout, it can be tedious to set these up every time. However, new documents can be created from templates using the “new from template” command in the file menu. First, locate the “templates” folder in the main Inkscape folder, which should be under “C:/Program Files/Inkscape/Share/Templates/” (Figure 3). The new template will now show up in the list when you use Templates (Ctrl+Alt+N). You can also save as “default.svg” and replace the default file in that folder. This will cause your template to be used whenever a new instance of the program is opened.


Figure 3. The Inkscape Templates folder.

Setting preferences There are several places where user preferences can be set in Inkscape. The first is through Document Properties (Shift+Ctrl+D), which allows you to change the size and orientation of the page outlined in the workspace. The second is Preferences (Shift+Ctrl+P), which allows you to change a large number of options related to individual tools and menus. I recommend setting the “style of new objects” under the “Pencil” section to “this tool’s own style”, “remember and use last window’s geometry” and “save and restore dialogue status” under “Windows”, and changing the “Pen” tool shortcut to “F5” under “Shortcuts” -> “Context”.


3. Importing sketches/photographs Biological illustrations ideally start with a hand sketch or a photograph. Of course, you can lay down the vectors free hand, but it is much more efficient and accurate to trace an image. Inkscape can import nearly any sort of image, including .jpeg and .png file formats. In whatever way you digitize them, either by scanning or from a digital photograph, these images will become the template for your illustration. Working with Layers If you set up your docks as recommended in the last chapter, your workspace should have a Layers dock open on the right side (Figure 4). Think of layers in Inkscape like layers of an onion. Each one is separate and overlapping, thus allowing you to alter or select one part of a drawing without changing others. In the top part of the Layers dock is a window showing all the layers in your current workspace. Below this are several buttons that allow you to create, delete, and raise and lower layers. At the bottom is an “Opacity” bar, allowing you to adjust the transparency of a layer from 100 (opaque) to 0 (invisible).

Figure 4. The Layers dock.

If there are no Layers in the window, create one now with the “create layer” button and name it “sketch”. The highlight indicates the layer that is currently selected. You will notice the new layer has two icons to the left of the name, an eye, and a lock. Clicking the eye changes whether the layer is visible in the workspace, and clicking the lock prevents any changes from being made to that layer. It’s good practice to only keep those layers unlocked that you’re currently working on. You’ll note later that even selecting objects on a locked layer is impossible. Create several more layers; note that the program asks you whether you would like these new layers above or below the current selected. You can select objects from any layers that are unlocked, but you will


only produce new lines and paths on the layer currently selected.

Importing photographs/sketches Make sure the sketch layer is at the lowest position, select it, and press Ctrl+I. This will open the "Import" dialogue, also available under File-> "Import...". You can then choose the image from file. A second dialog follows with options related to image quality. It is usually best to leave these alone. The exception is if your images have such a large file size they slow your computer to a crawl. Images are usually quite large in scale, so it is best to zoom out from the page outline before importing. The image may take up most of the screen. You can import as many images as needed, but only one at a time. Resizing, rotating, flipping, and clipping Once you have an image imported, using the Select Tool (F1) click on the image. You should see a dashed bounding box appear, along with some arrows (Figure 5). Click the image again, and the arrows turn sideways. In the first case, the image can be adjusted in scale, and in the second, the image can be rotated. These transformations are produced by clicking the black arrows and dragging. Click again, and the arrows change to the scale adjustment. It can be dragged about in both modes. The crosshairs in the rotation mode can be dragged to change the center of rotation.

Figure 5. An image selected with the Select Tool. Note the dashed line bounding box and the resizing arrows.


Scale the image down so that it fits the page by using a corner arrow while holding down Ctrl. This will scale the image in the original proportions. Rotate the image by using the corner rotation arrows until it is in the correct position. Usually this is with the dorsum towards the top of the page and the body oriented in the left-lateral view. If you are looking at the right side of the organism, and assuming it is bilaterally symmetrical, you can flip the image horizontally by pressing "h" or vertically by pressing "v". These options can also be accessed in the select toolbar at the top of the workspace. When the image is positioned, remember to lock the "Sketch" layer so you do not make changes to your template while working. You may also desire to reduce the opacity of that layer using the opacity meter to make your vectors easier to see, but usually this is not necessary. If the important part of the image is only a small portion of the total, you can “clip” it to size. Unlike cropping, clipping is a reversible process. Using the Rectangle Tool (F4), draw a square over the top of the relevant part of the image. The square should be opaque and solid colored (you can adjust this under the Stroke and Fill dock). Select the square, and then holding shift, select the image to be clipped, in that order (Figure 6). When both are selected, under the Object menu select “clip” -> “set”. Only the portion under the square will be visible. You can revert the image at any time with “clip” -> “release”.

Figure 6. Clipping images. Select the rectangle above the image first, then (holding shift) select the image. After clipping, the image appears as at right.


4. Outlining Once you have your sketch image positioned, it is time to draw the outline of your subject. This is the heart of the work, and usually the part that takes the most time. These lines are “paths”, meaning they are vectors described by an equation. Laying down the line Select the Bezier Tool (F5). In a layer above the sketch, start inserting nodes along the outline of the subject one at a time by left clicking (Figure 7). Most Inkscape tutorials will recommend using a small number of nodes for smooth curves, but biological objects are generally rough or irregular in outline. Thus, more nodes are usually better. You can also create smooth curves by clicking and dragging; when you release, you can adjust the shape of the curve. Don’t worry about smoothness, this can be adjusted later. If you misplace a node, simply press Delete and replace it. You can press Delete as many times as needed to remove previous nodes or to remove the path entirely.

Figure 7. Laying lines with the Bezier Tool. The square box is the start of the path. The currently active segment is highlighted in red, and other segments are highlighted in green.

When you have finished outlining an area, press Enter. The vector will turn the selected stroke color (Figure 8). If you pressed enter by accident, do not fret. Click the Bezier tool on one of the end nodes and you can continue where you left off. You can also close the path by clicking on the first node. This creates a single continuous path.


Figure 8. A completed Bezier Tool path. The squares indicate the start and end nodes of the path. Additional segments can be drawn to either end by clicking the pen on one of these nodes.

Adjusting lines Paths can be adjusted in one of two ways, either by changing the stroke paint and style in the Fill and Stroke dock, or by using the Node Tool (F2). If you click an object with the node tool, all the nodes in the object will be visible, and a bounding box will appear (Figure 9). Clicking an individual node highlights it, and you can now change its position. Clicking on a curve between two nodes highlight the two, and you can now change the shape of the curve by clicking and dragging. You can add a new node by double clicking a line section or by pressing the "New Node" button on the toolbar. Likewise, you can delete a note using the "Delete Node" button or by pressing the Delete key.


Figure 9. A path selected with the Node Tool. Each square is one node. Individual nodes or segments can be adjusted using the Node Tool.

By dragging a box around a group of nodes, you can select all of them at once. If you click the toolbar button "Make selected nodes smooth", all selected nodes will be changed from the default "corner node" setting to the smooth node setting. You can change nodes back to cornered with the adjacent toolbar button. The other two node types, the symmetrical and the auto-smooth, generally go unused as they produce too smooth of an outline for biological specimens. The smooth nodes, however, keep a nice irregularity if there are enough nodes present. Once you have all your nodes positioned correctly, turn them all into smooth nodes. There are likely a few that need to remain as cornered nodes, so select these, change them back into the cornered type, and adjust the lines as needed. Before continuing to the next part, it is best to adjust the stroke width as needed. This can be changed in the “Stroke Style” tab of the Fill and Stroke (Ctrl+Shift+F) dock (Figure 10). This is a stylistic choice; whether you decide to lead to the tweaking phase with all of your vector lines the same width or of different widths is up to you. In the past I have started with relatively wide stroke widths of up to 1.5, but now I tend to start with stroke widths of 1 or lower. Narrower lines to start seem to give my illustrations a more "classic" feel, and tend to give a rougher outline than those that start thicker. I often will make parts of an illustration that are heavier or closer to me have thicker lines to start, and parts that are more membranous, transparent, or further away from me have thinner lines to start. Again, it is a matter of personal style.


Figure 10. Stroke Style options in the Fill and Stroke dock.


5. Tweaking lines Once you have all of your lines positioned and adjusted, it is time to add some depth. There are two general ways to do this. Both of them involve transforming the outside boundaries of your vector paths (the “strokes”) to paths themselves. The first method involves manually changing the width of the paths using the Node Tool as described in the previous chapter. This can be effective, but is incredibly tedious and time consuming. The second, far more efficient method, is to use the Tweak Tool. The tweak tool Before using the tweak tool, the outline of the vector in question must be transformed into a path. Do so by selecting the vector and pressing the shortcut Ctrl+Alt+C, or by pressing the "Stroke to Path" button on the Node Tool toolbar. Or, through the Path Menu->"Stroke to Path". Make sure you are pleased with your node positions and line shapes before you do this, as these are difficult to adjust precisely after transforming strokes to path.

Figure 11. A path transformed using Stroke to Path. The normal outlines (strokes) of the path have been transformed into paths themselves. The line is now adjustable in width at each node and segment.

The new paths are the same shape as vector lines, except the boundaries of that line now have nodes (Figure 11). This allows you to adjust the width dynamically with the Tweak Tool (Shift+F2). Make sure the path is selected, and change to the Tweak Tool. All bounding boxes disappear (Figure 12). If no paths were selected, the tweak tool does nothing. It will only modify paths that are selected when it is activated. 16

Figure 12. A line selected with the Tweak Tool. When using the Tweak Tool, no bounding box appears around the path. The yellow circle cursor is the tools area of influence. Only lines selected when activating the Tweak Tool can be influenced; all other lines are unaffected.

The toolbar for the Tweak Tool has a large number of options, but only a few of them are useful for these circumstances (Figure 13). The “Width” sets the width of the tweak area, regardless of scale. The “Force” sets the strength of the tweaking force applied to the path. The modes determine how the path will be modified. The two applicable modes are the “Push Path” mode and the “Grow/Shrink mode”. The former will nudge a path length in a particular direction, and the latter will either increase (when Shift is pressed) or decrease the width of the line section. The final option is for “Fidelity”, which determines how close in shape the resulting path will be to the original. To use the path tool, click and drag along the length of path you wish to modify, and release. The slower and heavier you drag, the more the path will be altered.


Figure 13. A "tweaked" line. The Tweak Tool toolbar is shown at top.

Guidelines for tweaking line thickness Although your decision on how to use the Tweak Tool is entirely stylistic and personal, I have the following recommendations. ● Fidelity should be set to 95 or higher, such that the resulting line has a nearly identical shape to the original. ● Force should be set low. I never use a force higher than 10, and I often use a force of 1 when fine tuning widths. ● A larger width only means a wide area of alteration, but a tweak width zoomed out will often create a smoother feeling tweak than when zoomed in. ● Generally, a subject is depicted as if light is being projected directly down onto a subject and slightly up and to the left. Thus, areas that curve away from the viewer are often depicted with a darker outline than areas in your plane of vision. Thinner or membranous areas are usually depicted with a thinner outline. ● It is best to try to alter your lines in as smooth of passes as possible, or at as low of force as possible. This will give a more gradual and less abrupt feeling to changes in width. ● If you cause a line segment to disappear, do not panic! Press Ctrl+Z until it reappears. This indicates the force is set too high; decrease the force and increase the speed of the pass. ● If you are illustrating overlapping structures, you can tweak a gap between a path end and the other structure. Simply nudge the terminal section until it disappears, then adjust the terminal nodes until the gap is the size you desire. Further ways to achieve this are outlined in the next chapter. ● Tweaking paths seems to be as much an art as it is a skill. Finding a feel for how this


tool works requires a great deal of practice, but it pays off in much higher efficiency.


6. Detailing Now that you have your outlines finished, it is time to add details. These include clarifying lines for structures that are overlapping or that are entirely or partially covered. Make sure that details are located in a layer above the outlines, otherwise they will not always be visible. Distinguishing overlapping structures

Figure 14. A gap between two structures can show depth and the manner of overlap.

When two structures overlap, the most common way to illustrate this is to leave a gap in the line such that the underlying structure is incomplete and unjoined to the line of the overlying structure. The simplest way to achieve this is to draw the underlying structure such that the lines stop short of the overlying structure (Figure 14). If the lines are connected but should not be, you can use the tweak tool as noted in the previous chapter, or simply drag the nodes until they are not. A more complicated method is to draw a line at the point where the gap should be, adjust the width such that it does not overlap the lines of the overlying structure, and change the stroke paint to white (in the Fill and Stroke dock) (Figure 15).


Figure 15. Using white lines to show overlap.

Figure 16. Using dashed lines to show outlines of underlying structures.

Illustrating interior structures If two structures overlap but you wish to illustrate the underlying structure, you can do so with a dotted or dashed stroke style (Figure 16). Draw the outline of the structure


with the Bezier Tool, adjust the curve of the lines, and change the Stroke Style to one of the dashed or dotted forms. I recommend using a stroke width lower than of the uncovered structure and a fine dash.

Figure 17. Using a stripe pattern to depict internal/covered structures.

You can also depict internal structures with a single hatch pattern (Figure 17). Create a closed path the size and shape of the structure's area, and adjust as needed. Change the fill paint to "Pattern", and select "Stripe 1:1"; make sure the stroke paint is set to none. Using the node tool, adjust the angle of the hatch with the circle, the width of the hatching with the square, and the position of the hatch with the cross. This can be useful to distinguish between three or more overlapping structures. (Note: the square, cross, and circle may be located far away from your object; you may need to zoom out and search around the workspace for them.)


7. Setae and hairs In biological illustration, one of the most frustrating structures to illustrate is hair. This section is a specialized method to producing satisfactory insect setae or "hairs". While it likely will not apply directly to other fields, the method of using the Pencil tool to produce repetitive structures is widely applicable.

Figure 18. Pencil Tool paths drawn using different levels of "smooth". At the lowest smooth, every jitter of the hand is replicated. At the highest smooth, important details are lost.

Using the pencil tool Select the Pencil Tool (F6). In the pencil toolbar, "Smooth" changes the smoothness of the curves in the resulting line. "O" replicates every shake of the hand, and "100" always makes a straight line (Figure 18). I find that somewhere from 30 to 50 is a good setting. The "Shape" dropdown menu defines the shape of the resulting line. For tapered setae, choose "triangle in".


Figure 19. Drawing setae with the Pencil Tool.

To create a seta, start from the base. Left click, and in one smooth motion drag the shape of the seta onto the workspace (Figure 19). The line appears after releasing. Alternatively, you can click once to place the setal base and click where the apex should be. This will create a straight seta. Tweaking setae Pencil Tool vectors can be manipulated with the Node Tool just as with the Bezier Tool vectors (Figure 20). The shape of the seta can be adjusted by dragging the line segment, and the position of the base and apex can be adjusted by dragging the diamond nodes. In addition, the seta can also be adjusted in width by dragging the pink triangle at the base. More nodes can be added to the line segment to produce a greater curve. Thus you can create setae of any size or shape.


Figure 20. Adjusting setae with the Node Tool.

Creating setal annuli The setal annulus is the ring that surrounds the base of all true setae in Insects. If a seta is missing the setal annulus is visible in its absence and is usually visible when the seta is intact. Select the Circle Tool from the left side toolbar. Click and drag while holding down Ctrl to create a perfect circle. Change the fill paint to none and the stroke paint to black. Adjust the stroke width until the outline is thin but not invisible at the appropriate zoom level (Figure 21). Drag the annulus to the base of a seta, and adjust the radius to suit the setal width. Cut (Ctrl+X) the annulus, and paste it (Ctrl+V) at the base of every seta. Alternatively, while holding left click you can stamp the annulus at the setal base by pressing Spacebar. Smaller setae usually require smaller annuli.


Figure 21. Creating setal annuli

Adding setal outlines In some illustration styles, setae are drawn with a white outline. When these setae cross the outline of a structure, the white creates a visible gap in the outline. Inkscape does not have a particularly good way to replicate this, as stroke widths of 0.1 or greater tend to reduce the length of setae by covering their apices. I have experimented with stroke widths of 0.08 (Figure 22). While they are not completely satisfactory to me, this method may be of use to someone.


Figure 22. An example of a seta with a stroked outline in white.

Start by drawing a seta as stated above. In Fill and Stroke, change the stroke paint to white, and change the stroke width to 0.08 px. The seta should be surrounded by a narrow white line. Working from a pattern As the Pencil Tool allows you to set the Shape as "From clipboard", you can effectively make patterns for setal brushes similar to those used in Illustrator. This is particularly useful if you have a large number of very wide or oddly shaped setae that require each seta to be adjusted. Draw the shape of the seta using the Bezier Tool, Pencil Tool, Circle Tool, or some combination of the above. Make sure the pattern is straight and exactly in horizontal orientation (Figure 23). When ready, convert the object to a path if it is not already so, copy the pattern, and draw with the Pencil Tool. You will note that "triangle in" setae that were created from a pattern can no longer be adjusted in width.


Figure 23. Example seta patterns for use with "from clipboard" in the Pencil Tool.


8. Shading Vector image programs have less ability to create shading when compared with a raster program. However, it is relatively easy to shade with gradients in Inkscape. Other methods detailed below should be avoided. Using gradients The easiest way to produce shading in Inkscape is through a gradient. Draw a shape matching the outline of the shaded area. In the Fill and Stroke dock, change the Fill Paint to gradient. In the object there will now be a gradient between two or more colors (Figure 24). You can change the gradient colors and style by clicking "Edit gradient" in Fill and Stroke. The options appear as a toolbar. The width and direction of the gradient can be altered using the square and circle gradient nodes on the object.

Figure 24. An example gradient. The gradient toolbar is shown at top. Dragging on the circles will change the extent and angle of the shaded area. Dragging the square changes the center of the gradient.

Creating crosshatches If your intended shading is a very regular crosshatch design, you can create it using the Interpolation extension. Create a line length using the Bezier tool. Copy the length, and place it a short distance away. Align the two lines with the Align and Distribute Dock (Shift+Ctrl+A) such that they are parallel. Select both, and open Extensions->Generate from Path->Interpolate. Choose the number of interpolation steps from the dialogue, and click Apply. The extension will create that number of interpolated lines between the two originals. Copy the lines, paste and rotate the copy, and overlap them with the first 29

set (Figure 25).

Figure 25. An example crosshatch pattern. This was created using a combination of the Bezier Tool, the Interpolate extension, and the Tweak Tool.

{Ed.: I have not tried this, but I suppose a person could lay this sort of crosshatch over an entire drawing, convert the hatch to a path (Ctrl+Alt+C) and then use the Tweak Tool to create gradients in the hatch. The difficulty seems to be that with perfectly straight lines, there are only four nodes. The Tweak tool needs to start with a node point, and in this case it means starting at an end node. It seems that if the hatch was made very thin, and then roughened slightly using the tweak mode "Roughen", there would be enough nodes to alter the width at any point in the hatch. It is an interesting idea, and again I have not tried to completion, but I would like to see if someone can make it work.} Creating stippling The following methods are possible but not recommended, as large numbers of dots causes slow loading times and frozen windows. Every dot is an individual vector, thus, the program must calculate a large number of vectors to display the dots. I have used both of these methods, and I do not find them satisfactory. The simplest method uses the Pencil Tool to lay down dots one by one. When clicking with the Pencil while the Control key is pressed, the tool makes a small round dot (Figure 26). The dot size depends upon the default value in the Pencil Tool


preferences. Successive dots can be laid down in lines or semi-randomly as one wishes. This is, of course, a tedious process.

Figure 26. An example of stippling using the Pencil Tool. Each dot is laid down individually by holding Control and left-clicking.

A more complicated method uses the Interpolate extension. Follow the directions for creating crosshatches above, except using Pencil Tool dots. After the first interpolation, copy the line and paste it adjacent to the original. The lines should be alternating, such that the space in one is a dot in the other. Group (Ctrl+G) the two lines together, copy, and paste them parallel a distance apart. Interpolate in this manner several times. If the rows are lined up correctly, it should form a large square of neatly space alternating stipples. It also has the potential to crash your Inkscape window. You have been warned! As for the crosshatching tutorial, you can tweak the stippling to create darker and lighter areas of shading. Other options Other vector-based options, including the stippling software StippleGen, are far too complicated and difficult for everyday use. Post-processing in a raster image editor like GIMP is the best alternative.


9.Finishing When you're happy with a particular illustration, unless you decide to do some post-production work in GIMP or another program, it's ready to go! Well, almost ready. There are a few things you should do before publishing. Before starting these make sure your illustrations are the right size and position on the page, and remember to make new layers for the below items as appropriate! Creating a signature It's relatively easy to create a custom signature in Inkscape using the Calligraphy Tool. Select the Calligraphic tool and set the stroke paint to none and the fill paint to black. Also set the "preset" dropdown menu in the upper toolbar to "Dip pen" and the width to "1". You can play with the other settings to achieve the style you prefer. Sign your name, then resize and rotate it so it can fit near an external line of your illustration (Figure 27). You may also decide to save your signature in a separate pallet file for easy copy-pasting.

Figure 27. An example signature created with the Calligraphy Tool. The Calligraphy Toolbar is shown at top.

Inserting labels If you need to add labels or figure numbering, you can do so with the Text Tool (F8). Remember that the font size will change if you decide to later resize the illustration, so make sure you do this after you have your figure sizes correct. If illustrations from this file will later be used in designing a plate for a publication, you should hold off on figure labeling until then. As a now experienced Bezier Tool user, you can also easily add label lines pointing to structures (Figure 28). The lines can be made straight horizontal,


vertical, or at 45 degree angles by holding down Control.

Figure 28. Example of labeling using the Text Tool. Labeling lines have been added using the Bezier Tool.

The white background Inkscape exports with a transparent alpha channel background unless you create something else. This is why the layers in my template file includes a “white background” layer just above the sketch. Unlock the layer and draw a rectangle around the illustrations using the Rectangle Tool (F4) (Figure 29). Change the fill to white and hide the "sketch" layer (and any other layers you don't wish to see in the final drawing). If the size of the exported file doesn't equal the size of your box, then there is probably some potentially invisible line outside the white background rectangle; a wide sweep with the Selection Tool while zoomed far out should find anything you missed.


Figure 29. An example finished drawing with white background. The drawing is ready for export.

Exporting The Export dialogue is located in the File menu under "Export PNG Image...", or with Shift+Ctrl+E (Figure 30). You should select the "Drawing" button in the dialogue, unless your plate or figure fills the entire page. You can also select the visible area you wish to export with the Select Tool and use the "Selection" button to export only that.


Figure 30. The Export dialogue, with example image.

The "width" and "height" menus allow you to adjust the size of the resulting image, and the "dpi" menu allows you to change the density of pixels. 600 dpi is good for most purposes. The larger your drawing will be on paper, the higher the necessary density of pixels to avoid blocky pixelization. Anything much lower than 600 dpi will look pixelated on a web page. Higher dpi files will be much larger and take longer to export and upload. Click "Export As" and choose the file name of the exported image. Then click "Export". Congrats! Now only 50 more illustrations to do...


10. Conclusion When deciding between pieces of software for an artistic endeavor, cost is a major consideration. In this, Inkscape is a clear winner. However, there are other considerations, such as: Can the software do what I need it to present? What sort of artistic styles can the program successfully imitate? How much time and energy will it take to make an individual drawing? What is the learning curve? To this end, I’ve listed below some major differences between Inkscape and other types of artistic software. Inkscape is a vector-based drawing program. This allows you to scale images and change the shapes of lines without much fuss. Drawing with raster image programs like GIMP is much more like painting, allowing more free form expressiveness, but your images will always be subject to pixellization at higher magnification. Neither of these kinds of software are appropriate all of the time. Inkscape is not very good at shading. As shown in Chapter 8, it’s pretty easy to shade objects in a fuzzy way in Inkscape. But if you’re looking for a harder style like stippling or crosshatching, Adobe Illustrator or a raster image program like GIMP does a much better job. Inkscape is not very good with brushes. One of the most compelling reasons to use Illustrator over Inkscape is the ability to make custom brushes that are stored by the program. This is particularly useful for quickly painting setae, as you can paint both the annulus and the hair simultaneously. The closest Inkscape comes to replicating this is the “from clipboard” shape when using the Pencil tool. Inkscape is very good at adjusting path shapes. In Illustrator, the shape of the path length is determined at the time it was created. It’s not possible to alter the shapes of the paths after this. The same task is very easy in Inkscape. Inkscape is very good at styling paths to multiple widths. By transforming paths with “stroke to paths”, a single line can have an infinite number of widths along its entire length. This can be done very quickly with the Tweak tool, something that is impossible to do quickly in Illustrator. If Inkscape works for you, great! As Inscape is constantly being improved, this book is a work in progress. If you discover any fabulous new methods, if you have any questions, or if you just want to share your experiences using Inkscape, please send me an email (keroplatus (at) This copy is intended only to give the basics of line illustration. A future version will include more material on producing colored illustrations.


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