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In Automated Proofreading, One Equals Four

Photonics Spectra
May 2004
Hank Hogan

One machine eye equals four human ones. That's the formula used by manufacturers when following US Food and Drug Administration (FDA) guidelines for proofreading the inserts, labels, regulatory directives or other materials that accompany pharmaceuticals. Because the agency wants to ensure that such printed matter is accurate without fail, it mandates that materials destined for the public be proofread and inspected. There's a good reason for this vigilance.

In Automated Proofreading, One Equals Four
Automated proofreading systems evaluate the inserts, labels and other printed materials that accompany pharmaceuticals. Courtesy of Complete Inspection Systems Inc.

"The FDA has indicated over the years that label printing errors are one of the major reasons for product recall," explained Gary Parish, president of Complete Inspection Systems Inc. of Indialantic, Fla. The company makes systems for automated document inspection in pharmaceutical applications.

Under the recommendations, drug companies can perform manual or automated inspections. Manual inspections must involve two passes: a check and recheck. Automated systems must accurately detect defects, and that capability must be validated.

Many companies opt for the manual approach. Because of the complexity of some documents, however, a manual inspection can take eight hours or more. Moreover, because people are involved, errors can emerge as a result of fatigue or distraction.

The automated approach has its own problems. These materials can be quite large, up to 20 in. on a side. Consequently, an automated system must have a large field of view or face the problems of performing a step-and-repeat inspection, aligning different fields of view and handling the seams where the fields abut. What's more, some of the printed features aren't easy to see. A document may be missing a decimal point in eye-straining three-point type. To spot such features with 100 percent accuracy, an automated system must be able to scan documents at a resolution of 300 dots per inch or higher.

Nevertheless, Complete Inspection Systems' AutoProof Pro automated solution can handle this inspection task in a minute or two -- given the right machine vision capabilities. It is designed to accommodate documents up to 50 in. wide at scanning speeds of 10 in. per second and at resolutions of up to 800 dots per inch.

The system's software performs document matching by comparing two bit-mapped images and highlighting the differences as defects. "The difficult part is to realign the larger document pixel by pixel," Parish said. "We then are able to subtract the two using 256 shades of gray, and any differences are shown as either lighter or darker and are noted in a report." He added that an operator still makes the final decision because not all printed defects are of the same magnitude.

Although the company had used multiple CCD cameras in the automated systems to accomplish the imaging, today it makes use of a single, CMOS-based camera from Lumenera Corp. of Ottawa. Lumenera's business development manager, Greg Bell, said that the Infinity X was designed to be a flexible microscopy tool. It has a 1/2-in. color sensor with a 1280 × 1024-pixel array. Thanks to subpixel shifting, it is capable of resolutions of up to 20 megapixels.

The camera captures an image, rapidly shifts the sensor a fraction of a pixel by electromechanical means, captures another image and repeats the process. After acquiring the data, software algorithms combine the images, using the captured data and knowledge of the sensor's position to improve resolution. Lumenera contends that this combination of hardware and software allows the camera to increase its resolution until the limits of the optics are reached.

The adoption of a single camera simplifies Complete Inspection Systems' document-matching system and, consequently, cuts costs. Parish noted, however, that there are still some machine vision constraints to keep in mind -- for example, the interaction of the system's optics and the camera's resolution. This can be adversely affected by the sometimes less than perfectly flat nature of paper, which leads to valleys and rises in the document being scanned.

"Camera imaging requires accurate material handling to assure that the distance of the part to the camera is consistent, along with correct lighting and, of course, quality lenses," he said.


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