How Can a Camera Capture Very Subtle Differences Between Colors? Help

My client’s facility manufactures sunroofs for the automotive industry. Their factory is incredibly automated and uses multiple industrial robots for many of the manufacturing operations. They’ve asked me to come up with a video inspection & recording system to help them inspect the adhesive that is applied to the glass just prior to pressing the glass into place on the sunroof’s frame. A human inspector will be doing the inspection via a 1080P monitor. We’ve figured out the video recording elements of it so they’ll have a video record of each product during its inspection along with the product’s serial number.

The problem is obtaining a good image of the adhesive so the inspector can easily spot flaws (gaps or low areas mostly) in how the adhesive was applied. The adhesive is applied automatically by the robot holding the glass under an automated applicator (basically, a glue gun) which applies a bead of adhesive around the entire perimeter of the glass. The adhesive bead is about ½” wide with a triangular cross-section about ¾” high. The perimeter of the glass is painted a very dark flat gray (nearly black) – it’s painted about 3” wide all around the perimeter. A ¾” wide (roughly) stripe of black primer is applied onto the dark gray painted surface to help the adhesive do its job. My client is perfectly willing to program the robot so the glass (with the primer and adhesive applied) is repositioned about 3-4 feet in front of the camera and wait until the operator has viewed the monitor and is satisfied with the bead of adhesive. If OK, the robot (still holding the glass) moves it and presses it down into the frame before starting again on another piece of glass.

The problem is that everything is black or nearly black. The perimeter of the glass is a very dark flat gray, the primer is black (with a bit of gloss to it) and the adhesive is also black and is quite glossy. We started by using a 5MP IP camera from 3xLogic (VSX-5MP-D2) for the inspection and have experimented with a number of different cameras trying out cameras with WDR and IR. We also tried a B/W camera. And, of course, we've adjusted contrast, white levels, etc. Unfortunately, nothing we’ve tried can discern the difference in contrast between the blacks sufficiently for an inspector to spot any flaws. We’ve suggested using a different color adhesive and/or primer but that’s out of the question. For what it’s worth, they’ve been doing visual inspections for quite some time (i.e. the robot holds it up in front of an inspector) so there’s no problem with a human eye telling the difference. But we’ve yet to find a camera that can.

Sorry I can't include any photos or drawings -- my client's rules, not mine. Any suggestions would be very much appreciated.

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