Curve tools simplify the process of drawing curved lines on pictures in an image editor. You might find it next to impossible to draw perfect curves on your images without the aid of a curve tool. In Paint Tools SAI, the curve tool isn't available upon starting the program. After activating the tool and configuring it, however, you can accent any of your image's curves or add news one to it.
Launch Paint Tools SAI. Download and install a free copy of the program if you don't already have it (see Resources).
Click on SAI's "File" heading. Select the "Open" option from the file menu. Using the file explorer window that appears, select an image to import into SAI. Click "Open."
Click on the "Layer" heading, then select the "New Linework Layer" option in the context menu that appears beneath the heading.
Select a color for your curve. Click on the desired color in SAI's color palette. Select a size preset for your curve from the options in the box below the "Advanced Settings" heading.
Click on the "Curve" tool in SAI's toolbox. Right-click on the area in your image where you'd like your curve to start.
Click again at the location where you'd like to place the curve's peak or valley. Click on the image a third time to set the curve's endpoint. You can continue to add peaks and valleys to your curve, by clicking in new locations on the image. You can undo your curve's last addition by clicking your mouse's left button.
Double-click the mouse's right button to anchor your curve.
Select the "Save as" option from SAI's "File" heading to save a copy of your work.