Television – Special applications – Manufacturing
Patent
1997-04-02
2000-11-21
Rao, Andy
Television
Special applications
Manufacturing
356 71, 382 2, 382 8, 382 44, 382 45, 382 49, H04N 947
Patent
active
061510645
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the field of colour inspection and particularly, although not exclusively, to a method of control of a video camera for the acquisition of colour image data under varying image capture conditions.
BACKGROUND ART
In on-line manufacturing processes, for ink printed articles such as beverage cans, there is a problem of checking the colour consistency of the ink printing. In particular, there are problems in colour inspection, in capturing a colour image of a moving object on a production line; defining the areas of an article in which the colour is to be monitored, given the complex printed designs on the articles; and transforming a colour image signal into a uniform colour space and efficiently processing the colour image signal in the colour space.
DISCLOSURE OF THE INVENTION
An aim of the present invention is to provide a method and apparatus for effective non-contact colour monitoring of two or three dimensioned objects.
Another aim is to provide colour recognition and monitoring of colours on a multi coloured article.
According to one aspect of the present invention there is provided a method for controlling a video camera in a colour inspection apparatus for inspecting the colour of an object, the method comprising the steps of: colour error; and with the colour error signals, such as to correct the colour error in the captured image.
Specific methods of the present invention may have an advantage over conventional colorimeters or spectrophotometers, on which the object, on which colour is to be recognised must be presented in a flat state in contact with a measuring aperture of the instrument. This is inconvenient for products with curved surfaces eg. beverage cans.
The controllable parameters of the camera may include iris aperture setting; overall electronic gain of the image signals; electronic gain of the individual Red, Green or Blue components of the image signal; balance between the magnitudes of the Red, Green and Blue components of the image signal.
Preferably, the iris aperture and/or electronic gain of the camera are controlled so as to avoid saturation of the image signal.
Preferably, a red, green and blue signal component from a region of a captured image signal corresponding to a known colour object is obtained and
the iris aperture and/or overall electronic gain of the camera are controlled in accordance with a colour error signal derived from said red, green or blue signals of the region, such that saturation of said red, green or blue signals is avoided.
Preferably, the iris aperture and/or overall electronic gain of the camera are adjusted to achieve signals in accordance with the formula:
R, G or B signal=F.times.known R, G or B value
where F is a value less than unity.
Preferably, an imbalance between signals of a red channel, a green channel or a blue channel is rectified by controlling the electronic gain of each of the red or blue channels in accordance with a red channel or blue channel control signal corresponding to an image of an object colour of a predetermined red, green and blue balance.
Preferably, variations in successive red channel, green channel or blue channel signals corresponding to successive images of a same object are corrected by control of the iris aperture, overall electronic gain, the gain of each individual red, green or blue channel, or by control of the gain of a processed image signal processed in accordance with a computer program.
Preferably, said control is made in accordance with an image signal, or a component of an image signal, corresponding to a standard object of unvarying reflectance.
Preferably, said signal corresponding to a standard object is controlled so as to be constant.
Preferably, said control is made in accordance with a signal derived from a portion of an image corresponding to a calibration object of unvarying reflectance.
Preferably, said image is a separate calibration image.
Preferably, the light intensity response of the video camera is characterised by: reflectance; and a
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Connolly Christine
Leung Tin Wah William
An Shawn S.
Colour Valid Limited
Rao Andy
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