Colour imaging device

(54) Name: Color-based charging device

The present invention relates to imaging devices and more particularly to color image sensors.

Color image sensors of various types have been proposed for and used in camcorders. In order to avoid optical complexity and problems with image alignment, it is highly desirable that color image sensing takes place at a single imaging location, for example at a single, flat and light-sensitive network. However, difficulties arise with such a color image in a single location, since at least three different types of color information must be extracted to reproduce a color image video signal form.

A proposed way to achieve color image sensing in a single location requires the use of striped color filters superimposed on a single image sensor. Such filters that transmit a recurring sequence of three or more spectral bands are typically aligned vertically, and the image is scanned horizontally. In fact, elementary sensing areas are defined along the filter stripes. It will be appreciated that with this arrangement the sensing of a given color is not uniform in the horizontal and vertical directions. Such an arrangement is shown in U.S. Pat

892 883.

Although it is well known that the human eye has a greater resolution of the green color than it has for any of the colors red and blue, the prior art color imaging apparatus which has utilized this phenomenon has not provided the desired quality of because the color for which the eye has maximum resolution has only alternated with the other colors in the horizontal direction. It is pointed out that the above-mentioned American patent specification shows vertical stripes which alternate in the horizontal direction but not in the vertical direction.

Color imaging is performed by means of a single imaging network, which is composed of individual luminance and chrominance sensing elements, which are distributed according to type (sensitivity) in recurring, intertwined patterns, the luminance pattern having the highest occurring frequency and thus the highest image sensing frequency and both. vertical direction online.

In achieving a dominant luminance sensing, the relatively greater ability of the human visual system to discern luminance details is taken into account. By arranging the luminance element of the color image sensing network to appear in every other network position, a dominance of luminance elements in a pattern is achieved, which has the special advantage of uniformity in two mutually perpendicular directions (eg horizontal and vertical direction). In addition, by mixing three types of elements (luminance and first and second chrominance elements) in such a way that the luminance elements appear in every other network position and the first and second chrominance elements alternate with these luminance elements in their respective alternating rows in the network, a luminance-dominated sensing is achieved. which is uniform for all three color vectors in two mutually perpendicular directions. Certain desirable sensing properties, which result from the particular uniformity of such arrangements, are discussed in detail later.

In order to produce an element network according to the invention, a solids sensor network with broadband wavelength sensitivity is preferably provided with a superimposed filter mosaic. The mosaic filters are arranged one-to-one with elements in the sensor network and have light transmission properties in accordance with the intertwined patterns described above. Filters which are selectively transparent in the green region of the spectrum are preferably used in the production of luminance type elements, and filters which are selectively transparent in the red and blue spectral regions, respectively, are preferably used in the production of chrominance type elements. (The term luminance was used

7602578-2 herein in the broad sense as to the color vector, which is the main contribution to the luminance information. The term chrominance refers to the color vectors other than the luminance color vectors that provide a basis for determining an image.)

In an important alternative for realizing the invention, three interlaced patterns (a pattern of green-sensitive, a pattern of red-sensitive and a pattern of blue-sensitive elements) are arranged so that the green-sensitive elements (which serve to detect luminance) appear in every other mesh position, the red-sensitive elements alternate with these green-sensitive elements in every other row, as in the case of the presently preferred realization. In the remaining element positions, however, blue-sensitive elements alternate with red-sensitive elements to provide a luminance-dominated image sensing with a disproportionate chrominance sensing, which favors red over blue. With this arrangement, the sensing speeds of all three basic color vectors are set in accordance with the visual acuity of the human visual system. In other words, blue details, for which the human visual system has the lowest resolution, are detected with the lowest frequency, while green details, for which the human visual system is most sensitive, are detected with the highest frequency.

From the above, it will be appreciated that with selectively sensitive elements cooperating in interlaced sensing patterns according to the invention, the image information is derived during an efficient use of the sensing elements due to the fact that the relative image sensing frequencies are in fact set according to color in human sensitivities. . In addition, the uniformity of these interlaced sensing patterns achieves desirable sensing properties for a plurality of sensing element types (color sensitivities) that interact in a color imaging device.

Thus, according to the present invention, a color imaging device of the type specified in the preamble of claim 1 has the features specified in claim 1.

The invention will be described in more detail in the following with reference to the accompanying drawings. Fig. 1A is an exploded view showing preferred sensing element patterns for the application of the invention. Fig. 1B is a view corresponding to Fig. 1A. Figs. 2A and 2B are pattern representations showing a sensing property of preferred forms of the invention. Fig. 3A is a cross-sectional view showing a part of a row of sensing elements according to one

7602578-2 preferred embodiment of the invention. Fig. 3B is a cross-sectional view showing a portion of a row of sensing elements adjacent to the row represented in Fig. 3A. Fig. 4 is a perspective view showing a basic arrangement of elements for a camera system according to the invention. Fig. 5 is a block diagram illustrating signal processing devices which are useful in conjunction with sensing networks according to the invention. Fig. 6 is a plan view of another embodiment of the invention.

In Figs. 1A and 1B, to which reference will now be made, a group of three sensor patterns 2, 4 and 6, respectively, are shown, which are intertwined to form an image sensing network 8, each such pattern corresponding to a particular color vector. Pattern 2 (hereinafter referred to as the luminance pattern) has the highest element population and consists of luminance-sensitive elements (designated Y), which are arranged in every other element position. It will be appreciated that with this pattern the luminance elements (and thus the luminance detection) appear in half of the element positions in the network and are uniformly distributed over the entire network. First and second chrominance patterns 4 and 6 alternate with the luminance pattern in every other row to provide a composite sensing network without overlap. As a result of this arrangement, the sensing of an image is symmetrical for all three color vectors (ie the luminance vector and the first and second chrominance vectors) and uniform in two mutually perpendicular directions (eg horizontal direction and vertical direction) and is clearly shown in Fig. 1B.

Fig. 2A illustrates the progress achieved by the present invention over certain prior art. Referring to Fig. 2A, the distance between rows of elements in the horizontal and vertical directions is shown for the luminance pattern 2 (Fig. 1A) and for prior art striped element patterns (for example, when a vertical striped filter is superimposed on a sensor network). It can be seen from Fig. 2A that the luminance pattern 2 gives uniform sensing in the horizontal and vertical directions. For each row and column of elements, the luminance elements (and thus the luminance sensations) in Fig. 2A appear at regular intervals. In addition, the invention makes not only the luminance pattern but all other patterns (4 and 6 in Fig. 1A) in a sensor according to the invention regular and uniform in two mutually perpendicular directions.

The preferred luminance pattern has particularly desirable sensing qualities, which derive from its uniformity and orientation.

7602578-2

Of the possible patterns, which comprise only half of the element positions in a substantially rectangular network, the preferred pattern is that which gives the largest, usable area in the frequency space, i.e. the largest area in the frequency space which is free from the sensing signal interference. In addition, as a result of the orientation of the preferred pattern relative to the major axes, this useful area appears more extensive in the horizontal and vertical directions, i.e. in the directions where the human visual system is said to have the greatest resolution capability.

To further explain these sensing qualities, reference is made to Fig. 2B, where the sensing frequencies and harmonic frequencies of the preferred luminance pattern are graphically illustrated in the frequency space. Due to the uniformity of the preferred luminance sensing pattern, the horizontal and vertical sensing frequencies are equal. The Nyquist region or the only used frequency region, i.e. the region comprising frequencies closer to the origin than the sensing frequencies, is located in a substantially square portion of the frequency space (indicated by a dashed line), which portion diagonals are aligned with the horizontal and vertical directions (why the area has a greater extent in those directions).

Referring to Figs. 3A and 3B, a preferred imaging apparatus for realizing the invention utilizes a solid-state imaging network 20 of the charge-coupled type, which is comprised of individual sensor elements (e.g., element 22, which extends between the dashed lines in Fig. 3A). A filter mosaic 24 is superimposed on the imaging network 20, which mosaic comprises individual filters (eg a filter 26), each directed towards an individual sensor element in the network (eg the element 22). The individual filters in the mosaic 24, which form a filter mosaic over the net 20, are of the selectively transmitting type and are arranged in patterns in the manner described above. The letters G, R and B on individual filters in the mosaic 24 (Figs. 3A and 3B) serve to indicate the property of transmitting green, red and blue light, respectively, as used in the presently preferred form of the invention. Filters that selectively transmit light in the green area of ​​the spectrum are used to produce luminance-sensitive elements, while red and green light-transmitting filters are used to produce first and second chrominance-sensitive elements.

A selectively sensitive, color imaging element 26 is formed

7602578-2 of one of the filters 24 in combination with a sensor, such as the sensor 22.

It will be appreciated, however, that a network according to the invention could also be formed by sensors with selective wavelength sensitivity.

Fig. 4 shows a color imaging network 30 in a basic camera arrangement. Image information from individual rows in the network, such as a row 32, is transmitted to a shift register 34 (generally formed on the mapping network or tag) in response to signals from an interrogator, such as a row scan clock 36. This operation is well known and devices for performing it are described. in the literature and patents regarding charge-connected networks. It is also generally known how the output signal from the register is processed by means of a circuit 38. However, when using color mapping networks according to the invention, the information for the different color vectors is interleaved as a result of the mixed sensitivities of the color network elements. Accordingly, a switching circuit or switching network 40 is provided for dividing the image signal sequence into a useful form, for example, into parallel green, red and blue video signals.

In this form, the signals are converted in a conventional manner to a transmission form using a conversion matrix. This is especially appropriate if the number of rows in the grid corresponds to the number of lines in an image field scan (approximately 250 in the NTSC format) or the number of visible lines in an image (approximately 500 in the NTSC format), which are subfields.

A simplified diagram of a switching network 40 is shown in Fig. 5. Sampling / holding units 50 and 52 are used in alternating operation to separate green information and chrominance information, respectively. The latter alternates between red and blue for each successive row in the grid. Since red information and blue information are received on the basis of alternating lines, this information is stored in a register 54 for an entire row and is replaced in serial form when the luminance information of the next row arrives. To maintain the same output channels for red information and blue information independent of row, a switching means 56 switches the output connection from the register for each row of output information.

An important, alternative pattern set for realizing the color imaging net according to the invention is shown in Fig. 6. The luminance pattern (green), which has elements denoted by a G, assumes every other net position. A red pattern, the elements of which are denoted by an R ", alternates with the luminance elements in every other row, and red elements also alternate with blue elements to fill in

7G02578-2 405 193 ί the remaining element positions. Through this arrangement, the blue elements contribute only one-eighth of the element population, thereby taking into account the human visual system in¹ relatively limited ability to distinguish blue details. Red deer counts, for which the human visual system is more sensitive, avj is felt with a higher frequency than blue details as a result of the rela; ti vt larger population of red-sensitive elements. Luminance details, to which the human eye is most sensitive, are detected! of the largest population of elements. Through this arrangement, the image sensing is coordinated to closely correspond to the sensitivity of the human visual system, but it will be appreciated that the separation and storage of red and blue image information becomes more complicated when the red and blue patterns are different.

The invention has been described in detail with particular regard to realizations thereof, but it will be appreciated that variations and modifications may be made within the scope of the invention. As an example, | a variety of sensors are utilized, including the sensors in imaging networks of the charge-coupled device or charge-injector type. In addition, color-sensitive elements j useful in the invention may have inherent selective sensitivity or may include filters either at or at a distance from a sensor within a wide wavelength range, which filters selectively limit the sensitivity range of the individual sensors. Although the invention has been described in connection with a camera, it also has other areas of use, for example in connection with a presentation device.