Image analysis – Histogram processing
Patent
1995-09-27
1998-09-15
Boudreau, Leo H.
Image analysis
Histogram processing
382141, 382162, G06K 900
Patent
active
058091653
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for color control in the production process in which a sample and a reference of the sample are recorded pixel-by-pixel with the aid of the same arrangement consisting of one or more color sensitive image-forming sensors, in particular color matrix cameras, color line cameras or color sensitive point scanners.
Continuous control and monitoring of color fidelity of products is an important stage in quality assurance. In addition to manual qualitative monitoring of color fidelity by means of a visual comparison of the product colors with control cards or reference samples, there exists a well-developed color measurement technology for the purposes of quantitative determination of the color and/or color deviation of a sample in comparison to a reference.
Essentially, two classes of methods are used: product.
In the case of both methods, the structure of the surface, such as curvature in the space, applied textures, grooves, scratches or similar features, has a disruptive effect on the measurement results. The methods known to the art therefore also require that the color measurement is carried out on an essentially diffusely reflecting and even sample. Uneven spots, shining spots and spots in shadow must be absolutely avoided. It must also be ensured that only the color to be measured and no other color is present in the measurement window of the color measuring device, e.g. colored markings, imprints, labels or similar features. Since numerous products, e.g. extruded plastics for the production of floor coverings, ready lacquered bodywork parts, foodstuffs such as baked products, vegetables, printed products, etc., do not meet these prerequisites, the user must be satisfied with coloring small flat test models along with the products and measuring them later in the laboratory. It is therefore, for example, customary in the production of linoleum flooring to take samples from the extruded and colored floor covering material, to roll this onto flat cardboard surfaces, so that an even and diffuse surface results and to measure this sample in the color laboratory. This procedure is time consuming, manual and not directly part of the process; when the results are available, not inconsiderable batches have possibly already been produced with inadequate color fidelity.
In a method of the above-mentioned type known to the art from the document U.S. Pat. No. 4,812,904, in which a color video camera is used as an image-forming sensor, the color value signals delivered by the color video camera in the recording of the sample and in the recording of the reference are digitised pixel-by-pixel and stored. For the purpose of color control, the stored color vector components of the sample and the reference are statistically compared. This is done, for example, by forming the mean values of the color vector components for the sample and for the reference and determining whether the mean values of the color vector components of the sample deviate by more than a pre-set tolerance threshold from the mean values of the color vector components of the reference. The reduction of the comparison to mean values and to exceeding the pre-set tolerance thresholds results, however, only in a yes
o statement as to whether or not there is color deviation; on the other hand, no measure is obtained for the magnitude of the color deviation.
SUMMARY OF THE INVENTION
It is an object of the present invention to create a method of the kind mentioned at the beginning, which is capable of detecting the color deviation of a product quickly, continuously and to a large extent automatically and providing one or more color deviation measures for the magnitude of color deviation.
This object is solved according to a first embodiment of the invention by the following method steps: individual parts of the image field of the reference of the or each sensor recording the reference are put in the form of one or more multidimensional histograms of the color vector components and stored
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patent: 4812904 (1989-03-01), Maring et al.
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patent: 5278641 (1994-01-01), Sekizawa et al.
patent: 5307182 (1994-04-01), Maltz
patent: 5418895 (1995-05-01), Lee
Boudreau Leo H.
Ferguson Jr. Gerald J.
Mehta Bhavesh
Smith Evan R.
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