DE29520865U1 - CCD area sensors with color mosaic filter - Google Patents

Description

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CCD area sensors with color mosaic filter

The invention relates to CCD area sensors with color mosaic filters according to the preamble of claim 1.

For electronic image recording in electronic cameras, multiple arrangements of charge-coupled sensors, hereinafter referred to as CCD area sensors, have become widely accepted. These have light-sensitive, photoelectric image elements arranged in a matrix-like manner. The individual image elements, also referred to as pixels, are only sensitive to one color of visible light or one spectral range. To record colored structures, three image elements that are sensitive to the three primary colors red, green or blue must be assigned to one another in order to obtain an image cell of a color image.

When using three separate CCD area sensors with upstream color-selective splitter mirrors, the three image elements assigned to an image cell are located on separate components, so that high demands are placed on mutual adjustment. Furthermore, the costs are very high because three CCD sensors are required in each case.

In many cases, so-called mosaic filter area sensor CCDs are used as area sensors, in which three photoelectric image elements arranged next to each other, forming an image element triple, are sensitive to only one of the three spectral ranges (red, green, blue) through microscopically small color filters, also arranged in a matrix. Such an arrangement has the advantage that no special lenses or additional optical elements are required between the lens and the sensor.

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The disadvantage is that the various sensitive image elements are necessarily next to each other, i.e. not in the same place. With structures that are smaller than the width of such a triplet of image elements, there is a risk of color distortions occurring, which appear as so-called color moiré disturbances, particularly with periodic structures.

It has therefore been proposed to use optical means within the lens or in the space between the lens and the sensor to widen the image structures in the direction of the pixel triplets, which can reduce this color distortion. However, this inevitably results in a deterioration in the resolution of details in the pixel triplets. These usually extend in the line direction.

It has also been suggested that all image elements of the individual lines should be spectrally sensitive (so-called line-filter-area sensors), so that the image element triplets extend in the column direction. It has also been suggested that the regular image element sequence (R-G-B) in the row direction should be replaced by other sequences (e.g. R-G-G-B) and that the color patterns in the successive lines should be shifted or even by a quasi-stochastic arrangement.

0 Although this can achieve a reduction in the field element interference that varies depending on the structure, these arrangements have a number of disadvantages. These are particularly evident in a pseudo-stochastic filter arrangement, since when reading out the image element signals, it is necessary to determine in a relatively complex manner by comparing with an associated pattern table for each image element 5 whether the signal in question is assigned to a red, green or blue-sensitive image element.

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The effort required is even greater if a comparison of the signals of neighboring image elements is to be used to draw conclusions about the structure in the image and thus about the correction to be made for the incorrectly captured color component.

It is the object of the invention to further develop a CCD area sensor with color mosaic filter according to the preamble of claim 1 in such a way that a reduction in undesirable color distortions can be achieved with relatively simple means.

1Ö This object is achieved in a CCD area sensor with color mosaic filter according to the preamble of claim 1 by the features specified in the characterizing part of claim 1.

The invention advantageously reduces undesirable color distortions and thus improves the image. The image elements of the CCD area sensor are not strictly matrix-shaped, but are arranged in adjacent rows offset by a partial width of the image element width in the direction of the row. A key idea of the invention is that three adjacent image elements from at least two consecutive rows are assigned to an image cell. Preferably, two adjacent image elements from one row and a third, nearby or neighboring image element from an adjacent row are assigned to an image cell. This creates a triangular image element triple. However, it is also possible for the image elements to be distributed over three adjacent rows. Whichever assignment is chosen, each image cell should be assigned a closely adjacent sensor element of the primary color red, green or blue.

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As a result of the arrangement with image elements of an image cell distributed over two adjacent rows, image element triplets are created that better approximate the shape of a generally circular image point designed by a lens than is the case with the arrangement used previously, in which three elements are arranged next to one another. As a result, no additional optical means are required to deform the point image.

Triangular image element triplets result in a denser and more even coverage of the image plane. This is particularly the case when the individual image elements are not square but rectangular with, for example, an aspect ratio of around 3:4, with the longer edge aligned in the direction of the line.

When assigning individual image elements to image cells, the same image element can also be assigned to more than one image cell.

The charge transport in the row direction is carried out as with conventional CCDs. With image elements of an image cell distributed over two adjacent rows and a 4-phase control, the charges at the output for the even and odd rows appear offset by two phase clocks. While in an arrangement of the image elements as known from the prior art, the individual charges of the rows within the readout register represent different colors, in the present case according to the invention all signals of a column are chromatically the same. This makes reading and further processing much easier. In particular, the correlation with a color pattern required in a quasi-stochastic arrangement is eliminated.

25 Table.

Advantageous further developments of the subject matter of the invention are specified in the subclaims.

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Fair copy page 5

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The subject matter of the invention is explained in more detail below using exemplary embodiments with reference to the drawings. It shows:

Fig.1

Fig. 2a,b Fig. 3 Fig. 4 Fig. 5 Fig. 6

an example of an arrangement of the image elements and their assignment to an image cell according to the invention,

another allocation of image elements according to the invention,

an arrangement of rectangular image elements and their assignment to image lines according to the invention,

a schematic representation of a readout device for the picture elements according to the invention,

a schematic representation of another triggering device according to the invention,

Image elements with bevelled corners.

Fig. 1 shows a schematic of a CCD area sensor with a mosaic filter, which has image elements arranged in rows. The image elements are labeled R, G and B, respectively, according to their sensitivity to red, green and blue. Each row contains a regular, repeating sequence of image elements with the sequence R, G and B. The successive rows are offset from each other by half the width of an image element. If you look at the image elements that are each in a column, you can see that each column only contains chromatically identical image elements, namely only the image elements R or only G or only B.

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In Fig. 1, various possible assignments of the respective image elements R, G and B to image cells are shown. The image elements of an image cell are marked with a line

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You can see that every image element of an image cell is also an image element of another cell. In particular, two adjacent image elements are only assigned to an image cell in every second row, while the corresponding third is taken from the row in between.

It is assumed that the picture elements are square and the mutual distance in the row direction is a. The distance between two adjacent rows is a. If the picture elements are shifted row by row by half the picture element width, the distance between two consecutive columns for picture elements with the same color sensitivity is 1.5a, i.e. for columns with only R, G or B.

Fig. 2a and Fig. 2b show an arrangement of the image elements that differs from that of Fig. 1 due to a different type of allocation of the image elements to the image cells. Here too, the image elements of an image cell are enclosed by a line.

In Fig. 2a, the allocation of the picture elements to the picture cells is such that two neighboring picture elements are selected from each row for a picture cell and that the third picture element belonging to this picture cell is selected from the neighboring row. Furthermore, each picture element of a picture cell is simultaneously a picture element of two further, namely neighboring, picture cells. If the picture elements are assumed to be square with side length a, the distance between the centers of the picture cells in the row direction is also equal to a.

In Fig. 2b, the allocation of the picture elements to the picture cells is different, namely in such a way that two adjacent picture elements of a picture line are selected from each line, the third picture element belonging to this picture cell is selected from the adjacent line and two adjacent picture cells in the row direction each have two common

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picture elements. This topology means that the centers of such adjacent picture lines have a distance of a/2 in the line direction, if a is the mutual distance between the picture elements and that between the lines and the picture elements are square. This means that a better resolution is obtained without having to reduce the distances between the picture elements.

Other topologies are possible and can be derived from the above. For example, a picture element of a picture cell can be assigned to five other neighboring picture cells at the same time.

Fig. 3 shows an arrangement of rectangular image elements that have the dimension a in the row direction and the dimension 0.75 a in the column direction, i.e. the aspect ratio is 3:4. In this arrangement, the distances between the centers of neighboring image elements with the same color sensitivity are approximately the same, i.e. both in the row direction and in the column direction. This reduces the differences in resolution in the horizontal and vertical directions that occur in known regular arrangements with elements only in the row direction.

Fig. 4 shows an example of a readout device, generally designated 1, with which the image elements R, G, B of a 0 CCD area sensor with mosaic filter 2 arranged according to the invention can be read out. Three readout registers 3, 4 and 5 are provided for the image elements R, B and G. Each readout register 3, 4 and 5 is connected to an analog/digital converter 6 or 8, at the outputs of which digital signals for the colors red, green and blue are obtained for further processing.

5 It can be seen in Fig. 4 that when the CCD area sensor 2 is read out in the direction of the lines, the "position" of the respective image elements in the column of the CCD area sensor that has just been read out is reflected in each readout register 3, 4 or 5.

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Fig. 5 shows a readout device that differs from that shown in Fig. 4 in that it has only a single readout register 11 and only one analog/digital converter 12. In this case, the individual columns of the CCD area sensor 2 are read into this readout register 11 one after the other and then converted into digital signals by the analog/digital converter 12. In order to achieve the correct assignment of the output values of the image elements to the individual color image cells, these are read into a memory 13, from which they are read out with the help of a central processing device CPU 14 and converted into signals that are suitable for further processing.

The left half of Fig. 6 shows an exemplary arrangement according to the invention of image elements in the form of squares. The right half of Fig. 6 shows square elements whose corners have been bevelled. This can have a positive effect on the undesirable overflow of charges between the image elements. The corners can also be bevelled in the case of rectangular bundle elements.

The image structure was shown by reading a CCD area sensor that records the entire image. It is of course also possible to scan the image using the basic structure of a two-line CCD area sensor according to the invention.

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Claims (14)

1. Charge-coupled area sensor with a color-selective mosaic filter and matrix-shaped photoelectric image elements sensitive to the three primary colors red, green and blue, which are arranged in a regular, repeating sequence of the three primary colors red, Green and blue are characterized in that the picture elements (R, G, B) of two consecutive lines are each offset from one another by a partial width of a picture element in the line direction. 2. Charge-coupled area sensor according to claim 1, characterized characterized in that a picture element sensitive to red, blue and green is assigned to each picture cell, the picture elements being adjacent to one another and at least two of them being arranged in successive picture element rows. 3. Charge-coupled area sensor according to claim 2, characterized characterized in that two picture elements (eg R and G) from one row and one picture element (eg B) from an adjacent row are assigned to the same picture cell. 4. Charge-coupled area sensor according to one of the preceding claims, characterized in that at least one of the Image elements that are assigned to an image cell are assigned to at least one other image cell. B 3160 DE-11.01.1996 , ., ■ · · t · 4 · · 9 1 5. Charge-coupled area sensor according to claim 4, characterized characterized in that two image elements assigned to an image line are also assigned to at least one further image cell. 6. Charge-coupled area sensor according to one of the preceding Claims, characterized in that the picture elements are rectangular, the longer side being aligned in the line direction. 7. Charge-coupled area sensor according to claim 6, characterized in that the length ratio of the rectangular sides is 3:4. 8. Charge-coupled area sensor according to one of the preceding claims, characterized in that the center distance between two adjacent picture elements in the row direction is substantially equal to the distance between two adjacent picture elements in the column direction. 9. Charge-coupled area sensor according to one of the preceding claims, characterized in that the picture elements are substantially rectangular and their corners are bevelled or rounded. 10. Charge-coupled area sensor according to one of the preceding 0 claims, characterized in that the picture elements (R ₁ G, B) two consecutive lines are offset from each other by half the picture element width in the line direction. 11. Charge-coupled area sensor according to one of the preceding claims, characterized in that the outputs of the i I:\word\Ku\AN\B3160EN.doc B3160DE-11.01.1996 . .. .. Picture element rows are connected to three readout shift registers (3, 4, 5) in which the charges of adjacent columns can be stored and read out alternately in sequential order, whereby at the output of each shift register (3, 4, 5) only one signal for red, green or blue is available. Blue is available. 12. Charge-coupled area sensor according to claim 11, characterized characterized in that the outputs of the shift registers (3,4, 5) are each connected to the input of an analog/digital converter (6, 7, 8). 13. Charge-coupled area sensor according to one of claims 1 to 10, characterized in that the outputs of the image element rows are followed by a readout shift register (3, 4, 5), in which the charges of adjacent columns can be stored and read out alternately in sequential order. 14. Charge-coupled area sensor according to claim 13, characterized characterized in that the output of the shift register is connected to the input of an analogue/digital converter and that a memory for storing the signals of at least three consecutive columns is connected downstream of the analogue/digital converter, the memory content of which is determined by a 0 microcomputer to a digital image signal for red, green and blue _: can be assembled. tr:\word\Ku\AN\B3160EN.doc