DD236811A1 - METHOD AND ARRANGEMENT FOR THE OPTOELECTRONIC INFORMATION EFFECT OF CONTRASTING OBJECT STRUCTURES USING CCD COMPONENTS - Google Patents

Abstract

Method and arrangement for the optoelectronic information acquisition of high-contrast object structures with full utilization of the dynamic range of CCD components, wherein a first CCD component, the full light of the object structure, a second and optionally further CCD components, the light of the object structure via a filter or filter, respectively Increasing Absorbtionsvermoe it is fed that a selection of the pixel contents of the first CCD component with respect to their Saettigung takes place and only the ungesaettigten pixel contents are stored after an A / D conversion. When evaluating the pixel contents of the second and possibly each further CCD component, only the pixels of the respectively previously evaluated CCD component which are in the range of saturation are taken into account, whereby these in turn are checked for saturation and the unsaved ones are stored. This process is optionally carried out to the last CCD device whose upstream filter is such that no pixel can reach the Saettigung. Fig. 1

Description

For this 2 pages drawings

Field of application of the invention

This invention can be applied wherever CCD components are used for the optoelectronic information acquisition of high-contrast object structures.

Characteristic of the known technical solutions

If a single photosensor (pixel) of a line or matrix arrangement of such pixels has photons, these generate an electrical voltage as a function of their number. The characteristic curve between the number of photons and the pixel voltage generated is usually linear between U ₁₇₁ I _n and U _max , where Umi _n corresponds to the number of photons which generates such a voltage (just U _m i _n ) that just barely rises from the background, and U _max the smallest photo Nena number corresponds to, which generates such a voltage (U just _ma x), which does not increase further even when increasing the number of photo Nena. The dynamic range of a pixel is thus between UmI _n and U _max (or the adequate number of photons).

If the number of photons for generating U _{max is} exceeded at one pixel, this causes crosstalk to adjacent pixels and thus falsifies their information content. In the further course of the achievement of U _{max is} also referred to as saturation.

As a result, CCD components always operate in the range between U _m , _n and U _ma x ZU (dynamic range). Since the pixel area is constant due to production, the number of photons can only be controlled by the use of attenuation filters or the exposure time in which the pixel responds to incident photons (cycle time).

CCD components are mainly used for the optoelectronic conversion of areal light-dark distributions. There is always the problem of full utilization of the dynamic range while avoiding the saturation case. Both have not yet been solved satisfactorily in the common art in the prior art. In the prior art, an adjustment of the clock frequency or the use of attenuation filters so that at the brightest point of the areal light-dark distribution (ie at the location of the highest photon current) of the saturation case is just not reached. This method has the following disadvantages:

1. It must also be used when the brightest spot is only a fraction of the area to be inspected and the residual area offers photon flux far below that maximum. This dynamic range is given away considerably.

2. This method is not applicable if the brightest expected location can not be considered prior to measurement for calibration of the CCD (for example, in light biziques). The only solution is to expect an extremely high photon current, which in turn is associated with drastic dynamic range losses.

In DE-OS 2846662 an arrangement is discussed, which allows a change in the dynamic range with respect to the detection of light levels in lenses compared to such conventional design.

According to the invention for this purpose in a known iris a damping filter is used, which has a continuously increasing density, viewed from the edge of the filter to its center through which the optical axis passes, or has concentric rings, wherein the smallest circular area around the optical axis around it is the thickest. This device causes in addition to the dimming of the iris further damping.

The so-equipped lens downstream optoelectronic converter are thus able to process an increased contrast range than would be possible with a conventional lens.

Disadvantages of this solution are:

1. There is no automatic control of the aperture depending on the brightness provided. This must be done manually. Thus, this device is not suitable for automatically running processes with constantly changing contrast ratios.

2. When using CCD devices with areal extent and in the presence of brightness differences in the image field, the saturation case is possible in spite of the described device.

Object of the invention

The aim of the invention is to develop a method and to provide an arrangement which makes it possible to fully exploit the dynamic range of CCD components and to eliminate the drawbacks indicated in the prior art (use restrictions, no automation, avoidance of saturation).

Essence of the invention

The object of the invention is to develop a method with which the dynamic range of CCD components can be fully utilized without having to take into account the basic brightness and strong contrast fluctuations in the image field when viewing two-dimensional light-dark fields

 Furthermore, an arrangement for implementing this method is to be created.

The object is achieved with full utilization of the dynamic range of CCD devices whose pixel contents are supplied to a memory after an analog-to-digital conversion, according to the invention that in the read operation of a first, acted upon by the full light of the object structure CCD a test of Pixel content to saturation and only a storage of the unsaturated pixel contents is done and that in the read operation of a second and optionally each other CCD component, which is supplied to the light of the object structure via a filter or filter with increasing absorptive capacity, only the lying in the saturation region pixels Consider the previous CCD component and again only the unsaturated are supplied to the memory. This method is achieved by an arrangement consisting of a reflected or transmitted light illumination device for object structure illumination and optical Übertrager- and filter elements for transmitting and attenuating the optical information from the object structure to the CCD components according to the invention that at least two CCD components to a Object structure are aligned and are in optical communication with this on the optical transmission elements and that the first CCD component no gray filter, the second and optionally each other CCD gray filter elements are associated with each increasing absorbance.

The arrangement of the CCD components to each other is preferably to be made so that they are parallel to each other and that the number of the pixel of the respective CCD device, which first reaches a certain pixel in the scanning of the object structure with the pixel number of the following CCD device which next detects this picture element of the object structure.

Furthermore, depending on the memory size, the memory structure and the memory management, an orientation of the CCD components can be made such that they:

1. all at the same time consider the same picture element of the object structure and the readout of the pixel contents is clock-controlled serially,

2. Consider simultaneously different picture elements of the object structure and the reading out of the pixel contents takes place in a clock-controlled manner in parallel.

The gray filters for visual attenuation upstream of the CCD components, with the exception of the first CCD component, are arranged on the image side and have a precisely graded and increasing degree of attenuation from CCD component to CCD component. The CCD component, which is the last to be read out or lastly reaches a corresponding picture element of the object structure, must also be assigned the filter with the highest degree of attenuation.

The arrangement described ensures that a different characteristic of the photon current (pixel voltage) arises for the same picture element of the object structure in each CCD component, ie U _max occurs at a different number of photons in each CCD component, wherein the CCD component, which last omitted or last reached a certain pixel of the object structure, the largest number of photons to achieve U _max needed.

It makes sense to choose the attenuation at this last CCD device so large that the saturation case can no longer be achieved

 The described arrangement is supplemented by electronics, which has the following tasks:

1. If the i-th pixel of the first CCD component reaches the saturation voltage, the electronics ensure that not this value but the value of the ith pixel of the second CCD component is evaluated.

Also has this pixel saturation voltage, the i-th pixel of the third CCD device is evaluated, etc., so long until an i-th pixel of a K-th CCD device remains below the saturation voltage. Those pixels of the first CCD and the following ones, which remain below the saturation voltage, are evaluated the same.

2. If the K-CCD components do not register simultaneously, but successively identical picture elements, all signals of the pixels in which a value to be evaluated appears through a serially organized memory are recorded. This memory organization must therefore also ensure that the storage space for the ith pixel is kept free until the CCD reaches the pixel to be evaluated, from which a value below the saturation voltage is supplied. This can take in the worst case to the last CCD device.

embodiment

The invention will be explained in more detail below with reference to the drawings. FIG. 1: Spatial arrangement of the functional elements FIG. 2: Functional structure of the control electronics

In Fig. 1, an object structure 1, which is located on a coordinate table 2 with incident or transmitted light illuminated. There is an undamped mapping of pixels of the object structure via an optic 3, a prism 4 with the intensity Ι _Ί on the CCD component. 5

-3- 758

At the same time, a muted image of the image elements of the object structure via the splitter cube 6 and 7 on the CCD components 8, 9 and 10, in front of which there are gray filters, with the lntenitäten'l ₂ , 1 ₃ and I ₄ . This results in the following relationship:

I ₁ = undamped light

I ₂ <li

I ₃ <l ₂

U <l ₃

By relative movements of the coordinate table 2 relative to the optical components and the CCD components, a comb-shaped or meander-shaped scanning of the object structure takes place. 1. Measuring direction should be that which is perpendicular to the line length extension of the CCD components.

Furthermore, it is possible for the CCD components to record one after the other in each case a same picture element of the object structure. In this case, the distance of the CCD components to each other should be the same. At the time To, the CCD component 5 detects the picture element A of the object structure in the dimensions of the pixel width and the number of pixels. 2, the digitized voltage values of all the pixels which remain below the saturation voltage are stored via an electronic control system shown in FIG. At the time To + ΔΤ CCD device 8 detects the pixel A. Here is ensured by the control electronics, that only the pixels are considered, which were in the CCD device 5 in the saturation region. The pixels of the CCD 8, which now remain below the saturation voltage, are evaluated, i.e., their digitized voltage values are stored.

At time To + 2AT, pixel A is viewed through CCD 9 and the process is the same as for CCD 8. If necessary, this process is repeated until the last CCD component, unless all the remaining pixels in the case of a CCD component remain below the saturation voltage when viewing the pixel A. The control electronics must further ensure that all the pixels which are viewed by the CCD component 5 in the period To + ΔΤ, To + 2ATusw., Or by the subsequent CCD components are stored in digitized form.

The size of the required storage capacity of the memory increases in proportion to the distance between the first and second CCD components.

The achievable scanning speed depends on whether the video values are stored simultaneously or are available at the same time or via a multiplexer MUX.

The signal resolution of the analog-to-digital converter ADU is for example 4 bits, ie 2 ⁴ = 16 gray levels. The CCD components are adjusted to each other (by attenuation filter, inter alia) that their saturation values each correspond to the highest gray level (level 15). This results in a different absolute illumination difference per gray level per lighting level. For later retroactive calculation or further treatment of the illumination values, the voltage values of the individual CCD components are identified by a constant K1 to K4 (2-bit wide word) belonging to the respective CCD component.

The comparators KP 1 to KP 3 illustrated in FIG. 2 distinguish the video signals of the pixels according to whether they are larger than, equal to, or smaller than the gray level 15. All pixels with the rating <15 are written into the memory M according to their pixel address by being able to pass the TOR. The addresses of the pixels having voltage values corresponding to gray levels> 15 are stored in the memories M1, M2 and M3 corresponding to the illumination (filter) levels. The timing of the memories M 1 to M 3 coincides with that of the pixels.

The analog-to-digital converted video signals of the pixels of the CCD 5 are, if they have gray levels <15, written into the memory M 4 without delay, while the simultaneously read signals of the CCD components 8,9 and 10 in the registers RG1, RG 2 and RG 3 must be buffered.

The multiplexer MUX assigns the pixel signals of the three illumination levels to the memory M4, which is designed as a circulating memory. The respective memory level is selected by the circular memory controller STU.

The general control AST receives from the scanning means the clock of the picture lines to be scanned and in turn controls the pixel address control STS and the circulating memory control STU. The circulation memory control STU also controls the reading out of the video values of the pixels of the CCD components 5, 8, 9 and 10 from the circulating memory M4.

Claims (3)

-1- 758 claims: 1. A method for optoelectronic information acquisition of high-contrast object structures with full utilization of the dynamic range of CCD components, the pixel contents are fed to a memory after an analog-to-digital conversion, characterized in that in the read operation of a first, loaded with the full light of the object structure CCD Component, an examination of the pixel contents to saturation and only a storage of the unsaturated pixel contents and that in the read operation of a second and against each other CCD component to which the light of the object structure is fed via a filter or filter, each with increasing Absorbtionvermögen, only the be considered in the saturation region pixels of the respective previous CCD device and again only the unsaturated are supplied to the memory. 2. Arrangement according to item 1 for optoelectronic information acquisition of high-contrast object structures with full utilization of the dynamic range of CCD components, consisting of a Auflicht- or Transmitted light illumination device for object structure illumination and optical Übertrager- and filter elements for transmitting and attenuating the optical information from the object structure to the CCD devices gekennzeichne characterized in that at least two CCD components are aligned to an object structure and with this via the optical transmission elements in optical communication stand and that the first CCD component no gray filter, the second and optionally each other CCD component gray filter associated with each increasing absorptivity. 3. Arrangement according to item 2, characterized in that the gray filters are designed with increasing Absorbtionsvermögen as a gray wedge.