METHOD AND DEVICE FOR DETECTING A PREDETERMINED COLOUR

Abstract: The present invention concerns a method and arrangement for detecting a predetermined colour in a signal from a colour-sensitive CCD array using an analogue video technique. The input signal constitutes a measure of the intensity in at least three separate spectral bands, which can be combined to produce all visible colours. The method according to the invention is characterized in that upper and lower interval limits corresponding to the predetermined colour are defined for each spectral band. The signal corresponding to the intensity in the respective spectral band is then compared with these interval limits and an indication is received when the signal for the signal corresponding to the intensity of the spectral band lies within the permitted interval. The result of the detection process is represented by a binary output signal. The invention also concerns an arrangement for performing the method according to the invention.

Description: Method and device for detecting a predetermined colour The present invention concerns a method of detecting a predetermined colour in a signal from a colour-sensitive CCD array using an analogue video technique, which signal constitutes a measure of the intensity in three separate spectral bands which can be combined to produce all visible colours. The invention also concerns an arrangement for performing the method according to the invention. At present many attempts are made to determine the colour of an illuminated article, i.e. to perform a type of colour analysis. One way of performing such a colour analysis is to allow the reflected light to pass through a prism so that the light is divided into spectral colours. By weighting spectral colour components with a varying number of predetermined coefficients, it can be determined statistically and with a high degree of probability what the colours of the illuminated article are. This method per se gives a good result and enables a large number of colours to be determined but in many cases it is quite complicated and expensive since access to data-processing facilities are required for the statistical evaluation. The object of the present invention is to provide a method which can easily detect from a signal from a colour-sensitive CCD array using an analogue video technique whether an illuminated article has a given predetermined colour. This object is achieved in that: upper and lower interval limits corresponding to the predetermined colour are defined for respective spectral bands; the signal corresponding to the intensity of the respective band is compared with said interval limits; an indication is provided for each spectral band when the signal therefor lies within the permitted interval; and an output signal indicates whether the piedetemiined colour is detected. A particular characteristic of the method according to the invention is that the interval limits are defined by adjustment with respect to the predetermined colour in the conditions in which the detection process is to be performed. According to a further particular characteristic of the method according to the invention a visual indication that the signal for a spectral band lies within the permitted interval is provided by a light signal. Since the method is repeated for each colour, an unlimited number of colours can be detected. A further object of the present invention is to provide an arrangement for detecting a predetermined colour in a signal from a colour-sensitive CCD array using an analogue video technique, which signal constitutes a measure of the intensity in at least three separate spectral bands, which can be combined to produce all visible colours. The arrangement is characterized in that setting means are provided for defining upper and lower interval limits corresponding to the predetermined limits for the respective spectral bands; in that a comparator device operatively connected to the CCD array is arranged so as to compare the signal corresponding to the intensity in the respective spectral band with said interval limits; in that means operatively connected to said device are arranged to indicate when the signal for a spectral band lies within the permitted interval; and in that the arrangement is disposed such that it emits an output signal to indicate if the correct colour is detected. In the following the invention will be described in greater detail on the basis of a particular embodiment. In order to facilitate comprehension of the invention, the appended drawing shows the arrangement according to the invention as a block diagram. The arrangement according to the invention is preferably to be used for detecting articles which pass at relatively high speed on a conveyor track. The article can, for example, be a refuse sack, but any other type of article is also possible. The article for which it is to be established whether said article has a particular colour is illuminated with light of a predetermined colour, preferably white light. A CCD array 1 using an analogue video technique and whose output signal constitutes a representation of the light detected in three separate spectral bands is directed towards the article. At present it appears suitable to use a video camera for detecting the light reflected by the article. The type of camera to be used in no way restricts the invention. The camera 1 divides the colour into three different spectral bands, for example, red, green and blue, which each represent per se separate wavelength ranges and which can be combined so that substantially all the different colours of the spectrum can be formed. The output signal from the camera 1 comprises three electrical signals corresponding to the intensity in the respective spectral band. These signals are analogue, which means that the level of the signal for each spectral band is variable from zero to the highest level. An arrangement 2 according to the invention receives output signals from the camera. The arrangement 2 according to the invention is to be set up in the environment in which the arrangement is to be used. This means, for example, that when the arrangement is used for detecting an article moving on a conveyer belt, the camera 1 is to be mounted at the location at the side of the conveyor belt where this camera is to be operated by the conveyor belt, before the interval limits are set. It will be appreciated that the arrangement 2 according to the invention can be moved but the camera 1 must be subject to the same conditions when the interval limits are set as when the conveyor belt is operated. If the conditions in the environment of the camera change, the interval limit settings must also be changed. When the arrangement 2 according to the invention is set to the colour to be detected, the level of the above-mentioned electrical signal is used to define interval limits for an interval disposed about the signal level. This level is defined in the same way for each spectral band Setting can be performed when this function has been activated in setting means 3. In a particular embodiment of the arrangement according to the invention, two potentiometers are used for each of the signals corresponding to different spectral bands. The one potentiometer in each pair is set to the minimum of the permitted signal and the other potentiometer is set at the maximum of the permitted signal. This is brought about in that the potentiometers are first set in their end settings. The arrangement 2 according to the invention comprises means 5 for indicating the relation of the respective colour signal to an upper and lower limiting value. The embodiment in question uses light emitting diodes which, by means of a light signal, indicate whether a signal lies within a given range in order thereby to facilitate the setting process. When the potentiometers have been set in their end settings, the light emitting diodes indicate that the signal is in the interval defined by the potentiometers, since each visible colour can be set in this way. By reducing the interval defined by the potentiometers, i.e. the limiting values for a given colour, the arrangement can be disposed to emit an output signal only for the pi-edetermined colour. When the light emitting diodes indicate that the interval limits have been detected, these limiting values are fixed such that further variations of the limiting values are prevented until the setting function is re-activated. If a very particular colour is of interest, the interval has to be quite narrow, i.e. the low level is adjusted upwards and the high level is adjusted downwards. If, for example, the detection of white light is desired, the signals corresponding to the different spectral bands essentially have to be the same. In the case of red-green-blue signals the interval limits for each of the signals representing the red, blue or green wavelength ranges have to form an interval about the value which represents one- third of the total light reflected. The permitted highest and lowest interval limits have to lie quite close to one another. If, in contrast, the colour to be detected may be an entire colour scale, the permitted interval can be increased. In a particular embodiment the certainty that a given colour has correctly been detected can be increased by calculating a mean value of a number of input images. In this way the accuracy of the system can be increased when colour variations occur on the article to be detected, for example owing to undesired shadowing on the article. The demand for uniform colour quality on the article inspected is thus not as great. When the predetermined colour is detected, the signal which is received from the camera 1 is compared with the interval limits stored in the setting means 3 in a comparator device 4. If the camera signal falls within this interval, an appropriate output signal is received from this comparator device 4. This output signal is supplied to the device 5 which emits a light signal if the signal corresponds to the desired colour or colour interval. The speed at which the detection process occurs depends on the input speed of the camera. This means that as input speeds increase, the detection speed can be increased. The output signal from the arrangement according to the invention is preferably binary and can be produced in a number of different ways, for example by an opening/closing relay. The output signal is an indication of whether an article of the correct colour has been located in front of the camera; further processing of the coloured article can be based on this output signal. If the input signal to the arrangement 2 according to the invention does not consist of a signal divided into spectral bands, but of a signal containing a mixture of all colours, the arrangement according to the invention can be provided with an adapter at its input. This adapter can divide the incoming signal into at least three separate spectral bands by analyzing and filtering incoming spectra. The arrangement according to the invention can then, as explained above, be used to establish whether the input signal represents a given predetermined colour. By means of the method according to the invention it is also possible to detect a plurality of predetermined colours, as a result of the upper and lower interval limits being defined for respective parts of the spectral band for each predetermined colour. An arrangement for performing the method according to the invention for detecting a plurality of predetermined colours comprises setting means 3 for each colour, i.e. an assembly of potentiometers for each colour. These potentiometers are used in the above-mentioned way in order to indicate upper and lower interval limits adapted to the predetermined colour for each part of the spectral band. This means, for example, that in the case of an arrangement for detecting two predetermined colours, the number of potentiometers has to be doubled in relation to the number required in the case of the arrangement for detecting one predetermined colour or colour scale, in the case of an arrangement for detecting three colours, three times the number of potentiometers is required correspondingly. Similarly in an arrangement according to the invention for detecting a plurality of predetermined colours the comparator device 4 is arranged to carry out comparisons with the interval limits defined for respective colours. The manner in which this arrangement for detecting a plurality of colours is to be brought about is self-evident for a person skilled in the art in the light of the above description for detecting a p--^eteπnined colour or colour scale. In order to facilitate the setting of interval limits separately for a comparatively large number of colours, a microprocessor is preferably employed which is used in the manner well- known to a person skilled in the art.

Claims: CLAIMS 1. Method of detecting a predetermined colour in a signal from a colour- sensitive CCD array using an analogue video technique, which signal consti¬ tutes a measure of the intensity in at least three separate spectral bands, which can be combined to produce all visible colours, characterized in that upper and lower interval limits corresponding to the predetermined colour are defined for each spectral band; in that the signal corresponding to the intensity in the respective spectral band is compared with these interval limits; in that an indication is received for each spectral band when the signal therfor lies within the permitted interval; and in that an output signal indicates whether the predetermined colour is detected. 2. Method according to claim 1, characterized in that the interval limits are defined by adjustment with respect to the predetermined colour in the conditions in which the detection process is to be performed. 3. Method according to either of the preceding claims, characterized in that a light emitting diode illuminates in order to indicate visually that the signal for a spectral band lies within the permitted interval. 4. Method according to any one of the preceding claims, characterized in that an unlimited number of colours can be detected by repeating the method for each colour. 5. Arrangement for detecting a predetermined colour in a signal from a colour- sensitive CCD array using an analogue video technique, which signal constitutes a measure of the intensity in at least three separate spectral bands, which can be combined to produce all visible colours, characterized in that setting means (3) are arranged such that they define for each spectral band upper and lower interval limits corresponding to the predetermined colour; in that a comparator device (4) operatively connected to said CCD array is arranged to compare the signal corresponding to the intensity in the o respective spectral band with said interval limits; in that the comparator device (4) is operatively connected to means (5) for indicating when the signal for a spectral band lies within the permitted interval; and in that the arrangement (2) is disposed to emit an output signal to indicate if the correct colour is detected 6. Arrangement according to claim 5, characterized in that the setting means (3) for defining upper and lower interval limits corresponding to the predetei-mined colour are arranged to be adjusted with respect to the pre- determined colour in the conditions in which the detection process is to be performed 7. Arrangement according to claim 5, characterized in that the setting means (3) comprises potentiometers corresponding to each interval limit. 8. Arrangement according to any one of the preceding claims, character¬ ize d in that means (5) operatively connected to the comparator device (4) indicate when the signal for a given spectral band lies within the permitted interval, which means comprises a light emitting diode corresponding to a spectral band. 9. Arrangement according to any one of the preceding claims, character¬ ize d in that it comprises for each colour a setting means (3) for defining upper and lower interval limits corresponding to the pre¬ determined colour for each spectral band. AMENDED CLAIMS [received by the International Bureau on 10 May 1996 (10.05.96); original claims 1-9 replaced by amended claims 1-10 (2 pages)] 1. Method of detecting a predetermined colour of e.g. bin bags, which on e.g. a transport track, with a relatively high speed are passing a colour-sensitive CCD array using an analogue video technique, which signal constitutes a measure of the intensity in at least three separate spectral bands, which can be combined to produce all visible colours, characterized in that upper and lower interval limits corresponding to the predetermined colour are defined for each spectral band; in that the signal corresponding to the intensity in the respective spectral band is compared with these interval limits; in that an indication is received for each spectral band when the signal therfor lies within the permitted interval; and in that an output signal indicates whether the predetermined colour is detected. 2. Method according to claim 1, characterized in that the interval limits are defined by adjustment with respect to the predetermined colour in the conditions in which the detection process is to be performed. 3. Method according to claim 1, characterized in that a light emitting diode illuminates in order to indicate visually that the signal for a spectral band lies within the permitted interval. 4. Method according to claim 2, characterized in that a light emitting diode illuminates in order to indicate visually that the signal for a spectral band lies within the permitted interval. 5. Method according to any one of the preceding claims, characterized in that an unlimited number of colours can be detected by repeating the method for each colour. 6. Arrangement for detecting a predetermined colour of e.g. pin bags, which on e.g. a transport track, with a relatively high speed are passing a colour-sensitive CCD array using an analogue video technique, which signal constitutes a measure of the intensity in at least three separate spectral bands, which can be combined to produce all visible colours, characterized in that setting means (3) are arranged such that they define for each spectral band upper and lower interval limits corresponding to the predetermined colour; in that a comparator device (4) operatively connected to said CCD array is arranged to compare the signal corresponding to the intensity in the respective spectral band with said interval limits; in that the comparator device (4) is operatively connected to means (5) for indicating when the signal for a spectral band lies within the permitted interval; and in tiiat the arrangement (2) is disposed to emit an output signal to indicate if the correct colour is detected. 7. Arrangement according to claim 6, characterized in that the setting means (3) for defining upper and lower interval limits corresponding to the predetermined colour are arranged to be adjusted with respect to the pre- determined colour in the conditions in which the detection process is to be performed. 8. Arrangement according to claim 6, characterized in that the setting means (3) comprises potentiometers corresponding to each interval limit. 9. Arrangement according to claim 6, characterized in that means (5) operatively connected to the comparator device (4) indicate when the signal for a given spectral band lies within the permitted interval, which means comprises a light emitting diode corresponding to a spectral band. 10. Arrangement according to any one of the preceding claims, character¬ ized in that it comprises for each predetermined colour a setting means (3) for defining upper and lower interval limits corresponding to the pre¬ determined colour for each spectral band.

Inventors: BAADHOLM SVEN, BAADHOLM, SVEN
Applicants: BAADHOLM SVEN, WAHLQUISTS VERKSTAEDER AB, AB WAHLQUISTS VERKSTAEDER, BAADHOLM, SVEN
Application year: 1996
Main classification: G01J3
IPC codes: G01J3