Use GIMP to add color to your line art.
GIMP is a free, open-source graphics-editing program. It is a popular alternative to Adobe Photoshop, the industry standard tool for digital graphics professionals. GIMP offers many of the same features as Photoshop, and like Photoshop it does far more than just edit photographs. You can create graphics from scratch in GIMP using a variety of drawing tools and augment existing drawings and artwork as well. If you have access to a scanner, you can scan in your line art drawings and use GIMP to fill them with color.
1. Launch GIMP, and open the line art image file you want to color.
2. Click the “Colors” menu, and then choose “Threshold.” This feature is designed to restrict the dynamic range of the image to black and white only. If used correctly, ink smudges and eraser marks will be removed so that only your lines remain. Click “Auto” to get started, and then experiment with the two sliders below the graph to see how the image is affected. Try to find settings that make all your lines bold and intact without introducing artifacts elsewhere in the image. Your drawing should ideally look like a page in a children’s coloring book. Keep the “Preview” check box enabled so you can see the image change as you make adjustments. Click “OK” to apply the Threshold effect when you’re satisfied.
3. Click the Paint Bucket tool in the Toolbox or press “Shift” +”B” to select it. Click the upper rectangle in the display underneath the icons in the Toolbox to select a color. In the dialog that appears, click the tabs along the top to reveal different color models, and choose your color using the one you prefer. Click “OK.”
4. Click with the Paint Bucket tool to fill a region of the image with the color you chose. Your lines determine the boundaries for the colored area. Fill in as many areas as you like, changing colors as necessary, to color the whole drawing.
5. Use the Pencil tool to correct a line if you find a “leak,” or break in a line that allows color to fill a larger area than you intended. Select the Zoom tool by pressing “Z.” Click on the break in the line until it’s reasonably large in the display, and then press “N” to select the pencil tool. Type “Circle(01)” into the “Brush” field in the bottom part of the Toolbox (you only have to do this the first time). Change the color to black, and then click and drag the pencil tool to bridge the gap in the line and plug the leak. Press the “grave” key (which is also the “tilde” key) to quickly restore the zoom, and then continue with the Paint Bucket. If you find yourself making corrections like this often, consider starting over from scratch and changing your threshold settings to keep your lines intact.
6. Click the “File” menu, and then choose “Save As” to save the colored version of your line art. Choose a name and location for the file, and click “Save.” Your original scanned file is not overwritten, so you can use it again later.