DD248013A1 - PROCEDURE FOR IMAGE RECORDING WITH LINE-SENSE IMAGE SENSORS - Google Patents

Abstract

The invention relates to a method for image acquisition with line-shaped image sensors, for obtaining images of preferably already one-dimensionally screened image templates and for reducing the image errors resulting from the resampling. In order to achieve this, a relative movement between line-shaped image sensor and image original is expressed in such a way that the damped oscillatory movements occurring during the stepwise relative movement in the step pauses are synchronized with the image integration time about the positioning target point by appropriate mechanical dimensioning of the device carrying out the relative movement (FIG. 1). , whereby an artistic broadening of the scanning aperture is achieved. Fig. 1

Description

embodiment

The invention will be explained in more detail by the following example.

The application of the method in the scanning of rastered image templates, for example photographs of television images, has a particularly advantageous effect on viewing the result image. In this case, an adaptation of the original sampling pattern to that of the image sensor is virtually impossible, and moire as a result of insufficient compliance with the sampling theorem is particularly troublesome in periodic structures.

In the stepwise relative movement, the moving system responds with a transient response that depends on the mass, the damping and the rigidity of the system components, which corresponds to a PT ₂ behavior if the parameters mentioned are dimensioned accordingly. (Fig. 1)

If the beginning and end of the integration time Ti coincide expediently with passages of the oscillating system through the positioning target point Z ₀ , the MuF of the oscillating image recording system in the direction of motion can be approximately specified as Fourier transform of the aperture function:

| Σ

η - number of oscillations caused by the positioning target point Z ₀ at the beginning of the integration time T | m - number of further oscillations due to the positioning target point z ₀ at the end of the integration time T | Ji (x) - Bessel function of the first order of the i order

f- spatial frequency in the direction of movement

k- damping constant

j - imaginary unit

i, I - counting indices

With the positioning distance Z ₀ , the sampling conditions are set and the result is:

the sampling frequency in the direction of movement

χ _ 1

^T A -

and the Nyquist frequency characterizing the system resolution in the direction of movement

A ^f A 1

For example, with η = 2, m = 2, k = 0.8, it is possible to design the component of the system transmission function generated by the transient response such that the frequency components of the magnitude spectrum that cause the moire are in the interval (f _N , f _A ). on the other hand, the phase spectrum in the interval (Ο, Ϊν) has no significant nonlinearities or polarity changes.

With the expression of the transfer function shown, the positioning distance z _o is set so that:

f _A >-> f _N s - period of the interfering structure (Fig. 3), s

which is a compromise between the borderline cases

(i) f _A = -, (practically unattainable raster adaptation of image template and image acquisition system) and

(ii) f _N = -, (condition for complying with the sampling theorem)

is found. (Fig.4)

The properties of the image recording system according to the invention are achieved in the application of a CCD line sensor in that the temporal oscillation behavior of the device performing the relative movement with the times of the beginning and end of the integration time T | is synchronized in a predetermined tolerance range, which is realized by the mechanical dimensioning of the vibrating device according to the required integration time. The oscillatory behavior (FIG. 1) is so pronounced that in a time phase 1 from the rest position by the jump excitation the positioning target point z reaches ₀ and in that time the image charge peak from the sensor is completely closed. With the η th swing through the positioning target point begins time phase 2, the duration of the integration time T | equivalent. This is followed by time phase 3, in which the oscillation of the system is additionally attenuated in such a way that with the subsequent jump excitation the condition condition for a step response which corresponds to a PT ₂ behavior is fulfilled, the image charge readout begins and the time cycle is restarted, until the image is completely scanned. The same initial conditions and the mechanical properties guarantee the same scanning conditions for each new scanning operation.

Claims (3)

Invention claim: A method of image-taking with cellular image sensors, wherein a cell-shaped image sensor is moved stepwise relative to the optical axis, characterized in that the movement is a damped vibration generated by stepping in the step pauses around the positioning target point. 2. The method according to item 1, characterized in that the image integration time of the cellular image sensor is suitably synchronized with the temporal oscillation behavior of the relative movement. 3. The method according to item 1 and 2, characterized in that after completion of the image integration time, the damped oscillation is brought to a subsidence by additional damping. For this 2 pages drawings Field of application of the invention The invention relates to a method for image acquisition with cellular image sensors, which is used to obtain images of preferably already one-dimensionally screened templates and to reduce the image errors resulting from the resampling. The field of application of the invention is the use in image recording systems, preferably in the facsimile transmission and the scanning of image templates in the reproduction technique. Characteristic of the known technical solutions It is known (Huck, F. 0, Fales, C. L; Park, SK; Samms, RW; Self, MD: SPIE, 397, San Diego, 1983), theory analysis of sensor array-imaging systems for computer vision , Pp. 87-97) that defocusing has a degrading effect on the modulation transfer function (MTF) in order to suppress high spatial frequencies, especially those which can lead to moire. The disadvantage is that the optical MTF has an oscillating character when defocusing is present and does not drop monotonically. The degradation exists in all directions of the image plane. It is also known that the reduction of moire in the scanning rastered templates by arbitrarily aligned linear relative movement between the original and a diaphragm, the aperture, which has any geometric shape corresponding to the integer multiple of the area of a grid of the template takes place. (DE OS3217752) It is necessary that the template has no geometric distortions, which is practically not guaranteed when using television technical templates. It is also known that in order to reduce errors by sub-scanning, especially moire in screened originals, serpentine scanning lines are produced on the sensor by a scanning laser beam which is reflected onto the document via a complicated mechanical system. (DE OS 3126272) Object of the invention It is an object of the invention to carry out "image recording with cell-shaped image sensors" image recording of preferably one-dimensionally screened image templates such that the image errors resulting from resampling are reduced most likely. Explanation of the essence of the invention It is an object of the invention "Image recording method with cellular image sensors" to suppress the occurrence of image errors by resampling preferably one-dimensionally screened image templates, which appear as disturbing moire, by utilizing the mechanical proper movements of the image recording device solved that the mechanical properties of an image pickup device consisting of slide and image sensor device including optics, one or both of which realize the stepwise relative movement of the image original and cell-shaped sensor are so pronounced that the oscillations occurring as a result of the jump excitation are advantageously exploited of the projection optical device is projected onto the cellular sensor. As a result of the step positioning, a section of the image subject is subject to a vibration which is reflected in the motion direction around the positioning target point. By means of low mechanical damping it is achieved that during an integration time adapted to the lighting conditions, the amplitude of oscillation is only slightly smaller than the cutting width (scanning line spacing), so that the aperture of the scanning sensor elements is artificially widened in the direction of movement, which leads to a smearing of the image in one direction in which the formation of moire is most likely, without affecting the orthogonal image direction. With the completion of the image integration of the k-th scan line, the stepwise relative motion device is attenuated to an extent such that the scan conditions for the (k + 1) th scan line as a result of the (k + 1) th positioning move are those of the previous k Correspond to samples. By synchronizing image integration and stepwise relative motion, the suppression of moire is performed the same for the entire image field.