Method for disturbance-component-free image acquisition by an electronic sensor
View Patent ↗In a fingerprint sensor that effects capacitive measurement, a sequence of fingerprint images is recorded while a finger is placed on to the sensor. By comparing the best image with previous images of the sequence, the real constituent parts of the present image are determined and the remaining constituent parts are eliminated from the best image. Thus, residual prints and disturbance components brought about by contamination of the bearing area can be eliminated from the fingerprint image.
1. A method for a disturbance-free image acquisition, which comprises the steps of:
providing an electronic sensor for capacitive measurement; continuously increasing a capacitive coupling between a given object to be imaged and the electronic sensor;
using the electronic sensor for recording a sequence of images during the process of increasing the coupling;
choosing one of the images from the sequence of images as a basic image according to predetermined criteria;
choosing from the sequence of images, at least one further image to be one of a correction image and used for determining the correction image; and
correcting the basic image by subtraction of the correction image.
2. The method according to claim 1 , which comprises:
setting up the electronic sensor to operate capacitively; and
increasing the coupling of the given object to be imaged to the electronic sensor by the given object approaching a sensor bearing area of the electronic sensor.
3. The method according to claim 1 , which comprises choosing the basic image to be the image which a pattern recognition algorithm recognizes as one of a most typical for a type of object to be imaged and as a most clearly pronounced.
4. The method according to claim 1 , which comprises choosing the further image for the correction image which, in the sequence of images, appears a specific predetermined number of images before the image chosen as the basic image.
5. The method according to claim 1 , which comprises determining the correction image by averaging over a plurality of images of the sequence of images.
6. The method according to claim 5 , which comprises carrying out a weighted averaging in which the images are taken into account to different extents.
7. The method according to claim 1 , which comprises using a fingerprint sensor as the electronic sensor and acquiring a fingerprint as the given object to be imaged.