Optical Mark Recognition

OPTICAL MARK RECOGNITION (OMR)

OMR Form

OMR Reader

'Optical mark recognition' is the process of capturing data by contrasting reflectivity at predetermined positions on a page. By shining a beam of light onto the paper the scanner is able to detect a marked area because it reflects less light than the blank areas of the paper. Some OMR devices use forms which are preprinted onto 'Transoptic' paper and measure the amount of light which passes through the paper, thus a mark on either side of the paper will reduce the amount of light passing through the paper.

It is generally distinguished from optical character recognition by the fact that a recognition engine is not required. That is, the marks are constructed in such a way that there is little chance of not reading the marks correctly. This does require the image to have high contrast and an easily-recognizable or irrelevant shape.

One of the most familiar applications of optical mark recognition is the use of #2 (HB in Europe) pencil bubble optical answer sheets in multiple choice question examinations. Students mark their answers, or other personal information, by darkening circles marked on a pre-printed sheet. Afterwards the sheet is automatically graded by a scanning machine. In most European countries, a horizontal or vertical 'tick' in a rectangular 'lozenge' is the most commonly used type of OMR form, the most familiar application being the UK National lottery form. Lozenge marks are a later technology and have the advantage of being easier to mark and easier to erase. The large 'bubble' marks are legacy technology from the very early OMR machines that were so insensitive a large mark was required for reliability. In most Asian countries, a special marker is used to fill in an optical answer sheet. Students, likewise mark answers or other information via darkening circles marked on a pre-printed sheet. Then the sheet is automatically graded by a scanning machine.

Another example of OMR is the recognition of scannable bar codes.

Recent improvements in OMR have led to various kinds of two dimensional bar codes called matrix codes. For example, United Parcel Service (UPS) now prints a two dimensional bar code on every package. The code is stored in a grid of black-and-white hexagons surrounding a bullseye-shaped finder pattern. These images include error-checking data, allowing for extremely accurate scanning even when the pattern is damaged.

Most of today's OMR applications work from mechanically generated images like bar codes. A smaller but still significant number of applications involve people filling in specialized forms. These forms are optimized for computer scanning, with careful registration in the printing, and careful design so that ambiguity is reduced to the minimum possible. Due to its extremely low error rate, low cost and ease-of-use, OMR is a popular method of tallying votes