pixel granularity with axis camera

[Greg McKaskle]

If you care more about precision than performance, you don't have to use the bounding box width. You can determine a location, say near the vertical center of the bounding rect, and use edge detection on the original image to find the distance between the vertical edges of the original monochrome image. That measurement can give subPixel accuracy. Though keep in mind that you can't make something from nothing. The accuracy improvement achievable and the technique is described in the Vision Concepts manual -- C:\Program Files\National Instruments\Vision\Documentation\NIVisionConcepts. chm. Chapter one covers edge definition.

As usual, it is easiest to experiment with this using Vision Assistant. Take your color image, extract the luminance plane, and use the Edge Detector(Simple Edge Tool, First and Last, with a large edge strength of like 200). The edge strength depends on the brightness of your ring light. Draw a line across the rectangle, and the graph will help you determine the actual strength that differentiates the edges. The X values are now subPixel and more accurate than the bounding box.

Greg McKaskle