The direction and structure of illumination is critically important to seeing features or defects on the object under inspection. Join Gregory Hollows, Director of Machine Vision Solutions, as he uses a real-world UPC bar code example to illustrate the effects of directional illumination on flat, matte surfaces and glossy surfaces.
Hi, I am Greg Hollows. Welcome to the Imaging Lab. In this video, we are going to spend some time talking about directional illumination. As we have seen in some earlier videos, the direction and structural illumination are critically important to what you're trying to see or visualize in the machine vision or imaging application. We have a couple of directional illumination pieces here on the table top. I think you can see in the video that we have some light streaming across the table. As you can see in the image that is coming up on the screen, directional illumination can have a variety of effects depending on the surface topography and the actual surface material that is there. Directional illumination can work very very well when we're trying to look at things like, let's say, a 2D barcode or information that is on the side of a box, something where we're able to get a certain amount of illumination on there and it comes off very clean and we get a high contrast image. Now the problem with directional illumination, again if we refer back to the image, some things that are highly gloss or specular surfaces, we get a lot of high amounts of reflectivity, and it is not necessarily even, or something that we can balance out in the system. It generally ends up in one spot being much hotter than another, creating a hot spot, when we get a rolling off of the illumination as in the example that you see here. Very close to the light source we have a lot of illumination. As we move out, things are getting lower and lower and lower. So, for simple applications for diffuse surfaces like, maybe, a table cloth or something that is a fabric, directional illumination works well where a flat finished sort of paper or something that is a printing that is not a high gloss finish, directional illumination will work very very well. Now as you'll see here, we have two different types. We have a spotlight and a bar light in this situation. Now the two different ones can be used depending on the size of the object and what needs to be seen. We are going to see later how something like this that is very long could be used on a curved surface and not something that is flat and get decent illumination, depending on the type of camera we can use. That is going to be in some of the more advanced topics that we cover, structured illumination. But for right now, directional illumination can be very very effective again for flat, matte finishes. You can click on any of the suggested videos on the page to take you to another illumination or imaging topic.