5 Replies Latest reply on Jan 4, 2011 12:31 PM by Kurt Gold

    Need help with gradients and blends

    Lou Dina Level 3

      In using Illustrator CS4 on a Mac  (OSX 10.6.3).I am colorizing a 3D CAD drawing of mechanical equipment for a brochure. I am nearly done, but have one troubling problem I don't know how to solve. The piping all uses gradients to simulate steel stainless and other rounded piping, with shading, etc. I have one element which is shaped like a large, flat-bottomed "U". I need the gradient to follow the contour of the "U", so the vertical portions are dark on the sides and brighter in the center, but the horizontal portion needs to have the dark portions of the gradient top and bottom, with the lighter color running horizontally. Unfortunately, this piping component isn't totally regular in shape, so it isn't exactly a "U".


      Here is what I have tried so far. The best result was to create three sections with no stroke, making sure the anchor points connect, then shading each one individually with a gradient fill. It was the best of the bunch, but not acceptable. I tried creating a gradient mesh, but the mesh tool and the menu command scatter a mesh all over the place and it doesn't seem to do too well. I also tried adding a separate "white highlight" and creating a blend of the two objects. These last two were very disappointing.


      If this were a pixel based image in Photoshop, it would be easy to carefully paint in the shading and highlights I want, but I need it to be vector based.


      Any ideas on how I can smooth and blend colors so I don't have hard interfaces between blends?


      Thanks, Lou

        • 1. Re: Need help with gradients and blends
          Doug Katz Level 4

          Can you do this:


          1. Use the Pen tool to draw a path that follows the centerline of the U, irregularity and all.


          2. Increase the stroke weight of the path to approximate the width of the piping that it represents and apply the shadow color.


          3. Paste a copy of the path in front (command-C; command-F) and reduce its weight (.25 pt or so) and apply the highlight color.


          4. Select both paths and create a blend.


          5. If need be, offset the top path (the highlight) so it isn't so perfect and reflects your light source.

          • 2. Re: Need help with gradients and blends
            JETalmage-71mYin Level 3



            Many users approach programs like Illustrator thinking there must be some instant feature specifically made for "metal on a curve" and so on, or some "trick" for accomplishing it. It's just not that way.


            Very realistic renderings of metallic surfaces have been done in vector drawing programs since their beginning. It's one of the most frequently asked questions, so the web is chock full of examples. Just Google for "metallic" and "Illustrator" or "Corel Draw" or any other vector drawing program. The principles shown will be very much the same, regardless.


            Conceptually, you work realistic surfaces the same way you do in any other medium, be it paint, airbrush, or Photoshop: You just draw the darks, lights, and reflections that you see within the limitations of the medium you are using. Giving specific how-to instructions is highly dependent upon seeing the example you are attempting to create, because rendering compound shaped metallic surfaces is more a matter of drawing reflections than anything else. Approaches to it are as varied as the lighting conditions and environments in which a metallic object may be found.


            That's not a cop-out; it's just the way it is. By way of example, look at the various metallic surfaces in this drawing (mirror, rims, hubcaps, headlight bezels, shock springs...) and notice the very different treatments. This drawing is entirely just stacks of ordinary vector paths with grad fills and/or blends (no meshes, no autotracing). Again, upon each metallic object, you basically just draw the reflections, highlights, and shadows that you see as separate objects. There's not really any "clever trick" to it. (There are, of course, principles of rendering metal that would apply to any medium.)




            You were on the right track when you were attempting Blends. In vector drawing programs, modeled shading is typically done with grads and blends, often in combination. (Grad meshes are a relatively recent construct, corresponding with the arrival of PostScript Level 3. But they are tedious and not particularly intuitive. Plus, you'll understand them better if you understand ordinary grads and blends first.)Normal grad fills are quite limited in their shapes (especially in Illustrator).


            Blends are more work to construct, but can be made to conform to any shape. But again, think in terms of the shapes of the reflections and shadows and highlights as individual objects, not in terms of trying to make all the paths you draw in the shape of the overall object's outlines.


            For basics, start this way:


            1. Fill the object with a base color or general grad fill. Think of this as the "underpainting" of the object.

            2. Draw the highlights in the shapes that you see them in the subject. Fill these with gradients that range from white to the base color (or from white to transparent, if the program supports that).

            3. Similarly draw the shadows in the shapes that you see them in the subject. Fill these with gradients that range from a darker tone to the base color.

            4. Add details such as the thin squiggly shapes that roughly parallel the edges of the object (and which are really dark reflections of the surroundings, like the ubiquitous horizon reflection that is so often drawn in chrome).

            Don't kill yourself over the detail. Use artistic judgement. Add just enough shapes to suggest the reflections, etc., and achieve interest; let the viewer's eye fill in the rest.


            Again, if you want to provide an image of a specific example that you want to render, some users here can help bump start you with a specific method; there are many "clever tricks" but there's no single "cookie cutter" method that works for every metallic situation, if convincing realism is what you are after.


            A few basic pointers about rendering with blends:


            • Blends work best if the two (or more) paths being blended have the same number of points and have the same direction.
            • In Illustrator, use the Specified Steps option. Don't go nuts with the number of steps. Use common sense. For example, if the blend spans a quarter-inch, and the tonal range is 20%, ask yourself, "How many steps do I really need? Can I detect an edge that spans less than 10% of a quarter-inch? Can I detect a tone difference of 2%?"
            • Realize that you can blend between two paths that have grad fills. For example, draw a kidney-shaped path. downscale a copy of it, inside the original. Select both and give them the same black-to-black grad fill. Blend them. Directselect just one path and change one of the black color stops to another color. Change the direction of the grad. Watch the interesting "satin" effects you can get this way.
            • The same principle applies when blending grads as when blending paths: Best and most predictable results are achieved when the number of color stops are the same, even if adjacent color stops are the same color.



            • 3. Re: Need help with gradients and blends
              Lou Dina Level 3



              Thanks for the great suggestions. I have a bit to learn regarding blends, gradients, mesh, etc. Doug, your suggestion was very helpful and was definitely better than my previous attempts. I'll experiment a bit more with it. JET, I have yet to try your suggestions, but they make a lot of sense to me.


              I appreciate the wonderful suggestions and will make use of them as I try to refine and close out this project. Good stuff going forward too.


              Thanks again, guys.


              Best reagards, Lou

              • 4. Re: Need help with gradients and blends
                StrongBeaver Level 3

                Is there a tutorial which that car was created ?