Optical mark recognition (OMR) collects data from people by identifying markings on a paper. OMR enables the hourly processing of hundreds or even thousands of documents. A common application of this technology is used in exams, where students mark cells as their answers. This allows for very fast automated grading of exam sheets.
Background
Many OMR devices have a scanner that shines a light onto a form. The device then looks at the contrasting reflectivity of the light at certain positions on the form. It will detect the black marks because they reflect less light than the blank areas on the form. Some OMR devices use forms that are printed on transoptic paper. The device can then measure the amount of light that passes through the paper. It will pick up any black marks on either side of the paper because they reduce the amount of light passing through. In contrast to the dedicated OMR device, desktop OMR software allows a user to create their own forms in a word processor or computer and print them on a laser printer. The OMR software then works with a common desktop image scanner with a document feeder to process the forms once filled out. OMR is generally distinguished from optical character recognition (OCR) by the fact that a complicated pattern recognition engine is not required. That is, the marks are constructed in such a way that there is little chance that the OMR device will not read them correctly. This does require the image to have high contrast and an easily recognizable or irrelevant shape. A related field to OMR and OCR is the recognition of barcodes, such as the UPC bar code found on product packaging. One of the most familiar applications of OMR is the use of #2 pencil (HB in Europe) bubble optical answer sheets in multiple choice question examinations. Students mark their answers, or other personal information, by darkening circles on a forms. The sheet is then graded by a scanning machine.
In the United States and most European countries, a horizontal or vertical "tick" in a rectangular "lozenge" is the most commonly used type of OMR form; The most familiar form in the United Kingdom is the UK National lottery form. Lozenge marks represent a later technology that is easier to mark and easier to erase. The large "bubble" marks are legacy technology from 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 by darkening circles marked on a pre-printed sheet. Then the sheet is automatically graded by a scanning machine. Many of today's OMR 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. OMR marks are also added to items of printed mail so folder inserter equipment can be used. The marks are added to each (normally facing/odd) page of a mail document and consist of a sequence of black dashes that folder inserter equipment scans in order to determine when the mail should be folded then inserted in an envelope.
Optical answer sheet
An optical answer sheet or bubble sheet is a special type of form used in multiple choice question examinations. OMR is used to detect answers. The Scantron Corporation creates many optical answer sheets, although certain uses require their own customized system. Optical answer sheets usually have a set of blank ovals or boxes that correspond to each question, often on separate sheets of paper. Bar codes may mark the sheet for automatic processing, and each series of ovals filled will return a certain value when read. In this way students' answers can be digitally recorded, or identity given.
Reading The first optical answer sheets were read by shining a light through the sheet and measuring how much of the light was blocked using phototubes on the opposite side. As some phototubes are mostly sensitive to the blue end of the visible spectrum, blue pens could not be used, as blue inks reflect and transmit blue light. Because of this, number two pencils had to be used to fill in the bubbles—graphite is a very opaque substance which absorbs or reflects most of the light which hits it. Modern optical answer sheets are read based on reflected light, measuring lightness and darkness. They do not need to be filled in with a number two pencil, though these are recommended over other types (this is due to the lighter marks made by higher-number pencils and the smudges from number 1 pencils). Black ink will be read, though many systems will ignore marks that are the same color the form is printed in. This also allows optical answer sheets to be double-sided because marks made on the opposite side will not interfere with reflectance readings as much as with opacity readings. Most systems accommodate for human error in filling in ovals imprecisely—as long as they do not stray into the other ovals and the oval is almost filled, the scanner will detect it as filled in.
Designing and printing There are specific dimensions of designing OMR sheets with 0.05 mm precision on scale. If the dimensions are not up to the precision scale, the accuracy of the OMR sheet may vary, so the sheet should be designed, printed and cut perfectly.
Single Part – Sheets are printed on 105 gsm to 120 gsm paper on A4/Legal sheets. Double Part (Carbonless) – Two sheets are printed; one on 105 gsm paper and one on 60-70 gsm paper on A4 sheets. The bottom of the first sheet and the top of the second sheet are chemically treated so that the impression of the first sheet comes on the second sheet. Three Part (Carbonless) – Three sheets are printed on one 105 gsm paper and the other two are printed on 60-70 gsm paper on A4 sheets. The bottom of the first sheet, the top and bottom of the second sheet, and the top of the third sheet are chemically treated so that the impression of the first sheet comes on the second and third sheets.
… excerpt ends here. Continue reading the full article.
