U.S. Philips Corporation

Antonius J Bruijns

Rudolph M Snoeren

Johannes Albert Luijendijk

Bartholomeus G Dillen

An image pick-up apparatus (1) for picking up a plurality of sub-images and combining them so as to form a composite image, including a correction unit (5) for correcting brightness values of the composite image. The correction unit (5) includes a selection unit (6) for selecting bright and dark parts from the sub-images. There is also provided an arithmetic unit (10) for deriving a gain correction factor from the bright parts and an offset correction term from the dark parts. The correction unit (5) also includes a multiplier unit (8) and an adder unit (9) for multiplying signal levels of a sub-image signal by the gain correction factor and for adding the offset correction term thereto. The image pick-up apparatus is used in an X-ray examination apparatus (20) for picking up an optical image on the exit window (32) of an X-ray image intensifier (24) and for supplying an electronic image signal for a high-resolution composite image so that image information in a medical X-ray image with small details can be suitably reproduced.

Composing an image from sub-images

An X-ray examination apparatus includes an X-ray image intensifier for deriving an optical image from an X-ray image. The optical image is picked up by means of an image pick-up apparatus which includes a correction unit which is arranged to form a dark image signal and to derive test image signals from the optical image. Correction values are derived on the basis of the test image signals and the dark image signal. The correction unit is arranged to form a dark image signal, to derive one or more test image signals from the optical image, and to derive the correction values from said test image signals and the dark image signal. The dark image signal is picked up in the absence of incident light on the image sensor. The test image signals have a signal level which represents brightness values of the optical image which have been amplified by individual gain values.

X-ray examination apparatus including an image pick-up apparatus with a

An X-ray device comprising an image pick-up system with at least two image sensors (11 and 12) and a control circuit (41) arranged so that the image sensors are not simultaneously but alternately sensitized in the cine mode. This arrangement enables the number of object images picked up per second to be increased in comparison with a similar system in which the sensors are simultaneously sensitized. When CCD sensors are used, the control circuit can also be arranged so that the integration time of the sensors becomes adjustable. These two steps reduce motion artefacts in images of quickly moving objects, for example images of a moving heart.

X-ray device

Compensating for vignetting (loss of brightness at the edge of an image) is achieved by electronically multiplying the pixel-values of the vignetted image by a gain characteristic so as to obtain an unperturbed image. A gain characteristic pertaining to a particular vignetting effect is formed by a set of correction factors for all pixels. These correction factors are obtained from the image of an object having a spatially homogeneous brightness distribution. Various gain characteristics can be stored so that vignetting is compensated for even when the adjustments of the imaging system are varied. When, in order to improve spatial resolution, the image formed on the output screen of an image intensifier in an x-ray examination apparatus is split into two sub-images which are subsequently recombined, the vignetting effects in either of the sub-images are inevitably different due to the use of a beam splitter. The vignetting is decomposed into vignetting effects in a horizontal and in a vertical direction in the recombined image. Correction for vignetting is achieved by multiplying decomposition factors pertaining to horizontal and to vertical vignetting.

Imaging system with means for compensating vignetting and x-ray

An imaging system includes an image pick-up device with an image sensor having a rectangular detection face which is subdivided into discrete detection sub-faces for converting a radiation intensity distribution on the detection face into an electric signal, the detection sub-faces being arranged in a matrix of n rows and p columns respectively dividing short and long sides of the detection face, an object plane and an optical system which images a radiation intensity distribution in a circle situated in the object plane onto an ellipse situated on the detection face in accordance with a compression factor m. The compression factor may be chosen so that the ellipse spans no more than p/2 columns of the detection face so that video images can be formed at twice the conventional rate. In the case of non-square detection sub-faces, the compression rate may be chosen so that the ellipse spans an equal number of rows and columns, thereby making each detection sub-face correspond to a square in the object plane. When several, mutually shifted image sensors are used, the compression rate of the optical system is adapted to correct a decrease in effective dimension of the detection sub-faces. A CCD sensor is used in an imaging system operating according to the NTSC standard by utilizing correct image compression.

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Eindhoven, Netherlands

Antonius J Bruijns