In this portion of my series of coloring tutorials I will cover how to use Inkscape to convert your comic art into vector format and then convert it back into a raster image. Doing this cleans up your line art and allows you to fill your art with color without fear of accumulating those evil little white jaggies between your color and your lines.
As I said in the introduction to this tutorial series, Inkscape is a freeware vector art program. I won’t claim that it has the same functionality as Illustrator or CorelDRAW, but it’s perfect for our purposes. So, go to the website, download, and install it.
I’m going to assume that you already have your line art ready as an image file. Personally, I like drawing my art by hand and scanning it in to the computer, but I know a lot of people do their drawing directly in their art program using a tablet. It doesn’t really matter what method you use to make your line art.
Preparing your art for Inkscape
This step is critical for scanned art, but not for art that is digitally drawn. If your comic is digitally drawn, skip ahead to the next section.
1. Open up your line art file in your favorite raster art program. I prefer Photoshop, myself.
2. Use the program’s Levels function to clean up your line art. Levels are a way to redefine what parts of your image are considered white, and what are considered black. In short, it’s a way to adjust the contrast of your piece- except it’s better than that. You can also adjust the median tones of your piece- the grays in between true black and true white.
In Photoshop you can access the Levels option by going to Image > Adjustments > Levels or by hitting ctrl+alt+L (in Windows, anyway). For other programs, search around in your menu- if your program is robust, it’s probably in there somewhere.
3. Once your Levels popup is open, click on the black and white sliders and slide them towards the middle. But not all the way! Just enough to create a nice contrast between your lines and your background. You may want to play around with sliding the gray slider as well, to see if that helps to strengthen your lines. Do not worry if your background isn’t totally white- Inkscape will simply overlook that. And do not make your likes so bold that you lose a lot of detail.
4. When you’ve adjusted your image to the point you’re happy with it, click on Okay.
5. Save a version of your comic in a standard image format. I prefer .jpg. Do not use a program-specific format like .psd (Photoshop’s proprietary format).
Importing to Inkscape
1. Open Inkscape. Go to the File menu and select Open. Find the image of your comic and open it.
2. Inkscape will likely give you a popup asking if you want to link or embed the image. Select Embed and click Okay. Inkscape will then import your image. This might take a bit, so be patient.
3. Once it has imported your image, click on it. Inkscape treats your entire comic as a single object, so you have to select it in order to affect it. Little arrows should appear all around the perimeter of your comic.
4. Go up to the Paths menu and select Trace Bitmap. This is the Inkscape function that will go over your comic and create a vector copy of it.
5. A new Trace Bitmap popup will appear with several settings that you can change. Make sure that the dot next to the Brightness Cutoff option is filled. Next to Brightness Cutoff there should be a Threshold setting along with a number.
The Brightness Cutoff setting determines at what point Inkscape separates the foreground, which it will convert to vector, from the background, which it will delete. The higher the value, the more of your image it will interpret to be something it wants to convert to vector. I find that a Brightness Cutoff Threshold of about .540 usually works pretty well for my comics.
If your Brightness Cutoff Threshold is too low, Inkscape won’t copy the lighter portions of your line art and you may end up with annoying gaps in your lines that will frustrate you when you have to fill them with color later.
6. Once you have set the Threshold click on the Okay button.
7. Inkscape will now take a little while to go over your image and convert it to vector. Again, be patient. When it is done, the popup will not go away. You’ll have to click on its little X to close it.
8. Click on your comic and drag it to one side. You’ll notice that there are actually two copies of your comic- the original, and the new vector version.
9. Click on the original and hit the Backspace key to delete it. You won’t need it.
10. Now to convert your cleaned up vector image back into a raster/bitmap image! (Note: Raster and bitmap are really the same thing) Click on the vector image to select it. Go up to the main menu and select Export Bitmap from the File menu.
11. A new popup will appear. Here you can enter the dimensions of the new image. I usually go with something around 4000 pixels wide, just to be safe. The length will adjust proportionally when you set the width. This is actually really big, but better too large than too small- I can scale it down later. Though an image that is really big is also a bad idea as it will take a long time to process and might crash the program. Really, anything beyond 9000 pixels wide is pretty excessive.
12. Next, select a save location and choose a new file name for your bitmap image. Click the Export button. It will take some time, but Inkscape will save your cleaned up image to the location you specify. The new image will be a .png file of your line art with a transparent background.
And that’s it!
Next time I will cover importing your file and using it to do flat coloring. I’ll talk about Photoshop exclusively, I’m afraid, but the principles behind it should carry over into other programs, too.