Adding Shading to Vector Objects
by Tom Coates

Date Posted: 08/21/2001 - Several of my recent Canvas images have used the same basic technique to add realistic looking shading to Vector objects. This method is limited to giving rounded edging to objects. It has the advantages that it is quick, easy, works on just about anything and allows you to adjust the original object’s inking after the shading is done. The basic concept behind this is to create a paint object of the same “shape” as the original vector shape. The paint object is given the desired shading. Then the paint object is placed on top of the vector object and the two are combined using the Hardlight Transfer Mode. Below I’ve shown graphically how this is achieved. The real trick is easily creating the proper shading in the paint object. This tutorial shows the method I use to create the shaded paint object.:



Create the original object, with the desired fill and stroke. Virtually any object or group of objects could be used. Create a duplicate of the original object, but switch the inks on the fill and stroke to solid black. I’m going to show all of these intermediate steps on a contrasting background to make things clearer. But the background is not necessary for the process to work.



Use Image > Area > Render to transform the black object into a grayscale paint object, at the final resolution you’ll want in your drawing (in this example, 72ppi) and use fine anti-aliasing. Also, give the rendering a Transparency Mask, which creates a channel mask on the Paint object. This will make something that looks an awful lot like the original black object, which you can now delete. Note that the transparent areas actually have a white fill which you don’t see. I’ve shown here what things would look like if you turned off the channel mask.



Next, reverse crop the paint object to give it some white border space. The extra space is needed during the later embossing and blurring steps. You can create the border manually by Control-dragging the edges, but I prefer to use the Menu palette Image > Area > Crop, and fill in the dialog box. I typically expand the area by 120 percent. Due to the transparency mask, you won’t see the effects of this operation directly. Again, I’ve shown here how things would look without the mask.



Use the Image > Filter > Stylize > Emboss filter to create the illusion of depth. On a black object, you get mostly grey, with white and black highlights. Note how the channel mask limits the areas where the effect is visible. You can now see the 3D shading starting to take form. The filter’s controls are your primary method of controlling the overall effect. Use Angle to control the apparent light direction. Height controls how far the shading will extend into the object’s interior. Small values give slightly rounded edges, while larger values can round the entire surface. The “Amount” control is usually set high enough to get full black and white in the dark and light areas. Above 100 usually does that. If you set it lower, you’ll get less intense shading.

 

Use the Gaussian Blur Filter to smooth the edges. As before, without the channel mask, things look pretty ugly. But when we only look at the masked image, we get a beautiful rounded edging. In this case I used a setting of 3.5 pixels. The values used have to be enough to blur the sharp edges created in the embossing step.



Finally turn on the Hardlight Transfer mode in the Transparency palette, and place the shading object over the original vector object. There’s usually a little bit of hand adjustment required to get the two to align optimally. It’s often desireable to group the two objects together.



Once you have the shading worked out, it’s possible to change the inks used on the original vector object. Just apply the new inks to see how they look. The shading will automatically be re-applied, Here I selected a veined-stone texture Ink.



Several additions can be made to this process. First, the intensity of the effect can be adjustedwithImage>Adjust>Contrast. This can make the shading more or less intense, which can be necessary depending on the lightness of the inks on the vector object, or the surface characteristics you are after. For example, shiny plastic surfaces often have sharper hightlights, with more contrast.

Likewise, the overall effect can be adjusted by using the other painting tools on the shading object. For example,usingImage>Adjust>Invert you can reverse the apparent direction of the lighting, by swapping dark and light areas. The Curves and Levels adjustments can also be of use to get the exact results you want. You can also hand-paint onto the shading object to add or remove shading as needed. For example, you might want one portion of the edges to be less rounded. Air brushing a bit of 50% grey on these areas will remove the shading effect. The Dodge or Burn tools can create new shaded areas by darkening and lightening the existing values.