Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1984-08-27
1986-07-22
Shepperd, John W.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358 27, H04N 973, H04N 968
Patent
active
046022775
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a colour correction process and to a system using said process. It is more particularly used in general public video photography, in colour visiophony (the transmission of the image of the speaker at the other end of a telephone conversation, also known as picture phone) and more generally in the processing of colour images and pictures.
Photographic correction processes are already known and particularly white adjusting processes appropriate for television cameras. The document FR-A-2464611 describes a procedure in which a completely white screen (or a screen having colours in a balanced state, i.e. with an equal signal white) is placed in front of the camera to be corrected. This screen is photographed and the camera circuits are corrected in such a way that the electrical colour signals which it produces effectively correspond to white.
To carry out this correction, the average colour perceived by the camera is measured by forming the mean value of the signals in complete images. This mean value is obtained in an identical manner by low pass filtering. By comparison with signals corresponding to equal energy white, it is possible to determine therefrom colour signals to modify an amplifier chain or adders until electrical signals are obtained which correspond to the equal energy white (R-Y=B-Y=0 or R, V, B in a ratio of 1). When this setting has been obtained, the camera is used normally for photographing or shooting a random scene, the setting being kept unchanged during this operation.
Thus, such a procedure does not supply a permanent correction process, because the setting is only made once and not corrected during the scene. Moreover, it assumes that a perfectly white screen is available, which is not always the case when shooting. Finally, this process is unable to correct an image having an inopportune colour cast, e.g. due to imperfect lighting.
The object of the invention is to obviate these disadvantages by proposing a system and a process which permits a permanent correction without using a reference screen. Moreover, the invention permits a large number of correction types and is no longer limited to adjusting just white.
These objectives are achieved by the following means: balanced), the image is analysed not by processing all the image signals, but only by taking certain samples corresponding to certain points of the image, the complete image, which makes it possible to obtain an average colour for the scene being photographed (and not as in the prior art an average colour corresponding to a white screen), colour obtained and are defined as a function of various criteria which, when applied to the samples taken, give corrected samples, which define a corrected average colour; applied to all the signals supplied by the camera and which are consequently corrected; reactualized by taking new samples.
It is readily apparent that such a process is very advantageous. First, it is permanently adapted to the instant scene as a result of a reactualization, which can be carried out for each new image. A new set of samples is then taken into account for each image and a new average colour obtained. However, the reactualization can be performed every N images (N a random integer) or only when the average colour varies excessively from a reference value.
The process according to the invention is also completely automatic and requires no intervention on the part of the operator (manipulation of white screens, coloured filters, etc).
Finally, it has considerable flexibility. Thus, the samples used for determining the average colour can be chosen either by sampling several points per image, or by sampling a single point per image, or by modifying the position of the image point or points between individual images in a predetermined or random manner, or by sampling points on groups of consecutive or non-consecutive images, etc.
With regard to the actual correction, the invention once again provides considerable flexibility. Naturally, an attempt can be made to reach a refe
REFERENCES:
patent: 3684825 (1972-08-01), Dischert et al.
patent: 3737561 (1973-06-01), Boer
patent: 4152720 (1979-05-01), Fenton
patent: 4335397 (1982-06-01), Tamura
patent: 4368482 (1983-01-01), Machida et al.
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