Image analysis – Histogram processing – For segmenting an image
Patent
1996-08-19
2000-05-16
Tran, Phuoc
Image analysis
Histogram processing
For segmenting an image
382172, G06K 900, G06K 934
Patent
active
060647620
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to a system and process for separating foreground information from a background information on a document, whereby the foreground information is superimposed in an arithmetic (e.g., either additive or subtractive) manner on the background information. The method is particularly suitable for determining a threshold value for a signal intensity of the background information on the document, for clarifying the background information on the document and also for converting electronic grey scales to black and white.
BACKGROUND OF THE ART
In employing electronic document processing it is frequently necessary, because of the quantity of data and to simplify subsequent processing, to convert electronic grey scale image data to black and white. In doing this, only text and numbers should be left as black and white information and not background patterns or pre-printed dropout colors, in order to obtain good legibility or to make it possible to effect subsequent electronic processing. For this it is necessary to be able to distinguish between the foreground containing information and the background, which generally contains no information but is structured, for example for safety or design reasons. If it is possible to distinguish between a foreground and a background, this allows the background to be removed, that is, suppression or cancellation of the background, in order to leave the foreground information.
For more certain subsequent processing of the foreground information it is necessary, in particular, to ensure that no component of the background flows into the foreground as an undesired artefact where it may lead to erroneous interpretations.
Black and white pictures, which should satisfy the requirements for subsequent electronic processing, frequently cannot be produced by the processes known from the current state of the art for background removal if the document has a highly structured background, as is the case for security reasons, for example, with the Eurocheque or an identity card. Highly structured backgrounds are generally backgrounds characterised by high contrasts which are preferably linear or like writing and exhibit structure dimensions which are of the same order as the dimensions of the written entry.
As an example of a document with a highly structured background FIG. 1 shows the currency and amounts field of a Eurocheque in grey scale representation. FIG. 2 shows the grey scale distribution along a horizontal line in FIG. 1. For this, the line was placed in the region between the handwritten and the machine-printed entries in the currency and amount field in such a way that it did not cut the entries. High values (in the "white" direction) represent a clear grey value and low values (in the "black" direction) represent dark grey values. With a conventional use of 256 grey values, grey value 0=black and grey value 255=white.
As can be seen from FIG. 2, the grey values of the background (not the frame) extend uniformly to a particular limit (threshold) which they generally, with a few exceptions such as, for example, as a result of framing or through image distortion, do not fall below. This results from the printing technology in manufacture in which the color saturation can be effectively controlled. This is generally also desired, otherwise the entries are also difficult for humans to read or may even become unreadable. The excursions below the threshold value in the "black" direction which can be clearly seen in FIG. 2 arise from the frame and the dividing line between the currency and the amount fields.
The grey value of the (handwritten and machine printed) entries, caused by the subtractive color behaviour of the most used printers, in each case lies below this threshold, however, often only very slightly. Consequently, the contrast with the background is considerably less pronounced than the contrast within the background. Subtractive colour behaviour in general means that additionally applied color pigments remove further colour compone
REFERENCES:
patent: 5280367 (1994-01-01), Zuniga
Beckstrand Shelley M
Gundel Norman L.
International Business Machines - Corporation
Tran Phuoc
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