Vision Basics - Camera Calibration and Lighting Black Level Similarly, if a given value, or offset, were added to all the pixels, the absolute brightness of the image would increase, making it easier to work with. Black Level is the ACE Sight para- meter that performs this function. If the value of Black Level is set too high, all the intensity values are bunched up around the high end of the scale and the images are washed out (sim- ilar to overexposing a piece of photographic film). Using Gain and Black Level together allows you to maximize the brightness and contrast within an image.
The binary threshold values are calculated after the effects of Gain and Black Level have been included in the image, so the difference between light and dark areas of the image is maximized and the binary image is most useful. Exposure, Gain, and Black Level can be set from the Edit window (within Acquisition Settings) of the Virtual Camera win- dow. Gain and Black Level should be adjusted after the camera Exposure has been set for max- imum contrast. Vision Basics - Camera Calibration and Lighting Camera Calibration Camera calibration is the process of relating the image size of the camera to the actual size of the field of view.
Two primary pieces of information are established when camera calibration is run: l The number of pixels needed to see a millimeter of distance in the field of view This relationship is used by any tools that make distance measurements. It is also used by vision-guided motion devices. l The ratio of the height of a pixel to its width See Standalone Camera Calibration on page 320. NOTE : The offset of the camera from the robot or other equipment is not part of this cal- ibration. That information is obtained after the standalone camera calibration. See ACE Sight Calibrations on page 625. Some important points to remember about camera calibration:
l The millimeter-to-pixel ratio is different for different camera-to-object distances. If you are making distance measurements of objects that are different distances from the camera, you have to create a calibration data set (virtual camera) for each dis- tance. l When you change the focus of a camera lens, the amount of the viewing area in the field of view changes. This means that the millimeter-to-pixel ratio changes, and cam- ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 311