Optical mark recognition

A response to an SAT math question marked on an 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.

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.[12] As some phototubes are mostly sensitive to the blue end of the visible spectrum,[13] 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.[12]

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.[12] 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.

Design of OMR Sheet – There are specific dimensions of designing OMR Sheet with 0.05 mm precision on scale. If the dimensions are not up to the precision scale the accuracy of OMR sheet may vary. So it is advisable that the sheet should be designed and printed with perfection and the cutting of the sheet should be perfect.

Types of OMR Sheet Single Part – Sheets are printed on 105 gsm to 120 gsm paper on A4/Legal sheet. Double Part (Carbonless) – Two Sheets are printed one 105 gsm paper and one on 60-70 gsm paper on A4 sheet . The bottom of first sheet and the top of second sheet is chemically treated so that the impression of the first sheet should come on the second sheet. Three Part (Carbonless) – Three Sheets are printed one 105 gsm paper and other two on 60-70 gsm paper on A4 sheet . The bottom of first sheet, the top and bottom of second sheet and the top of third sheet is chemically treated so that the impression of the first sheet should come on the second and third sheets.

It is possible for optical answer sheets to be printed incorrectly, such that all ovals will be read as filled. This occurs if the outline of the ovals is too thick, or is irregular. During the 2008 U.S. presidential election, this occurred with over 19,000 absentee ballots in the Georgia county of Gwinnett, and was discovered after around 10,000 had already been returned. The slight difference was not apparent to the naked eye, and was not detected until a test run was made in late October. This required all ballots to be transferred to correctly printed ones, by sequestered workers of the board of elections, under close observation by members of the Democratic and Republican (but not other) political parties, and county sheriff deputies. The transfer, by law, could not occur until election day (November 4).

One of the first OMR software packages that used images from common image scanners was Remark Office OMR, made by Gravic, Inc. (originally named Principia Products, Inc.). Remark Office OMR 1.0 was released in 1991.

The need for OMR software originated because early optical mark recognition systems used dedicated scanners and special pre-printed forms with drop-out colors and registration marks. Such forms typically cost US$0.10 to $0.19 a page.[14] In contrast, OMR software users design their own mark-sense forms with a word processor or built-in form editor, print them locally on a printer, and can save thousands of dollars on large numbers of forms.[15]

Identifying optical marks within a form, such as for processing census forms, has been offered by many forms-processing (Batch Transaction Capture) companies since the late 1980s. Mostly this is based on a bitonal image and pixel count with minimum and maximum pixel counts to eliminate extraneous marks, such as those erased with a dirty eraser that when converted into a black-and-white image (bitonal) can look like a legitimate mark. So this method can cause problems when a user changes their mind, and so some products started to use grayscale to better identify the intent of the marker—internally scantron and NCS scanners used grayscale.

OMR software is also used for adding OMR marks to mail documents so they can be scanned by folder inserter equipment. An example of OMR software is Mail Markup from UK developer Funasset Limited. This software allows the user to configure and select an OMR sequence then apply the OMR marks to mail documents prior to printing.

OMR betting form used in Japan Racing Association Fukushima Racecourse, Japan.

Betting ticket using this form.

There are many other applications for OMR, for examples:

• In the process of institutional research
• Community surveys
• Consumer surveys
• Tests and assessments
• Evaluations and feedback
• Data compilation
• Product evaluation
• Time sheets and inventory counts
• Membership subscription forms
• Lotteries and voting
• Geocoding (e.g. postal codes)
• Mortgage loan, banking, and insurance applications

OMR has different fields to provide the format the questioner desires. These fields include:

• Multiple, where there are several options but only one is chosen. For example, the form might ask for one of the options ABCDE; 12345; completely disagree, disagree, indifferent, agree, completely agree; or similar.
• Grid: the bubbles or lines are set up in a grid format for the user to fill in a phone number, name, ID number and so on.
• Add, total the answers to a single value
• Boolean, answering yes or no to all that apply
• Binary, answering yes or no to only one
• Dotted lines fields, developed by Smartshoot OMR, allow border dropping like traditional color dropping.

In the past and presently, some OMR systems require special paper, special ink and a special input reader (Bergeron, 1998). This restricts the types of questions that can be asked and does not allow for much variability when the form is being input. Progress in OMR now allows users to create and print their own forms and use a scanner (preferably with a document feeder) to read the information.[19] The user is able to arrange questions in a format that suits their needs while still being able to easily input the data.[20] OMR systems approach one hundred percent accuracy and only take 5 milliseconds on average to recognize marks.[19] Users can use squares, circles, ellipses and hexagons for the mark zone. The software can then be set to recognize filled in bubbles, crosses or check marks.

OMR can also be used for personal use. There are all-in-one printers in the market that will print the photos the user selects by filling in the bubbles for size and paper selection on an index sheet that has been printed. Once the sheet has been filled in, the individual places the sheet on the scanner to be scanned and the printer will print the photos according to the marks that were indicated.

There are also some disadvantages and limitations to OMR. If the user wants to gather large amounts of text, then OMR complicates the data collection.[21] There is also the possibility of missing data in the scanning process, and incorrectly or unnumbered pages can lead to their being scanned in the wrong order. Also, unless safeguards are in place, a page could be rescanned, providing duplicate data and skewing the data.[19]

As a result of the widespread adoption and ease of use of OMR, standardized examinations can consist primarily of multiple-choice questions, changing the nature of what is being tested.