Backlight illumination - diffuse
A technique positioning a diffuse illuminator behind the object to give a silhouette. This technique is normally used if 'through holes' or shapes are of interest, or the object is generally opaque with darker/brighter variations in the areas of interest.
The images show how the fill level of a bottle is being checked. The first image was taken under normal domestic lighting while the second image was captured using a high intensity backlight to create a clear image of the liquid surface which shows up as a dark line in the camera image that is then very easily detected by the software.
It is not easy to check the fill level of a brown bottle under normal domestic lighting.
Another common use for backlights is part presence verification. In the images the component has been transformed into a binary image that is much easier to examine for simple defects such as bent or missing connectors or for major damage.
