JP2007158575A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of taking video of the depth of field which is shallower than the limit determined by the size of an imaging element. <P>SOLUTION: A calculator 10 is supplied with video signals from imaging elements 3, 4, and 5, and a focal distance L between a subject and a lens 1 from a control unit 9, as well as, a measured distance Dn for each pixel measured with a range sensor 7. The measured distance Dn is applied with two-dimensioned vertical and horizontal direction low-pass filtering processings to obtain LPDn. Then, the absolute value of difference is calculated, between the LPDn and the focal distance L. The low-pass filtering characteristics which will be applied to video signals is changed, depending on the result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus capable of adjusting the depth of field.

  In recent years, digital still cameras equipped with a CCD as an image pickup element are becoming popular in place of cameras using film. Even in the video production market where movies were shot using 16mm film or 35mm film, it was shot with a digital video camera equipped with an electronic device such as a CCD or CMOS as the image sensor, and then processed for editing and composition. And digital cinema that performs everything up to projection digitally is spreading.

  Here, the depth of field is adjusted in order to shoot artistic images in cameras that are intended for still image shooting such as digital still cameras and cameras that are intended for video shooting such as video cameras. And shooting frequently. For example, when shooting a person as shown in FIG. 11 (portrait shooting), an image that is focused on the person and the background is moderately blurred is preferred as an artistic image with the person floating.

  The in-focus range before and after this focal length is called the depth of field. The smaller the depth of field (the shallower the depth), the more the background can be blurred and the portrait image can be taken.

  Here, the depth of field will be described with reference to FIG. In FIG. 12, reference numeral 1 denotes a lens, which is in focus at a distance L (solid line). However, in actuality, not only the subject at the distance L is focused, but the images before and after the distance L are also focused (broken line). This is because the blur cannot be detected if the blur of the image formed through the lens is smaller than a certain size. This size is called a permissible circle of confusion and is a parameter determined by the size of the image sensor.

  The range in focus behind the distance L is called the rear depth of field D1, and the range focused on the near side is called the front depth of field D2. The depth of field D is expressed by the sum D1 + D2. Here, the rear depth of field D1 and the forward depth of field D2 are expressed by the following equations where the focal length of the lens is f, the F number (aperture value) is Fno, and the allowable circle of confusion is δ.

  Therefore, the depth of field is expressed as (Equation 3).

  According to Patent Document 1, if a 35 mm film camera and a 1/2 inch CCD are focused on a 3 m subject from a lens in order to capture an image with the same angle of view, in the case of a 35 mm film camera, It is reported that the focus is in the range of 2.5 m to 3.7 m, and in the case of the 1/2 inch CCD camera, the focus is in the range of 1.7 m to 9.8 m. This is largely due to the size of the image sensor.

In addition, in order to shoot images with a shallow depth of field, in general, an ND filter is inserted after the lens to reduce the amount of light incident on the image sensor, and the aperture is opened (F-number is reduced). In doing so, techniques are used to shoot blurred images. Patent Document 2 provides a camera in which the depth of field is displayed in a graph on a viewfinder so that a photographer can easily check the depth of field. The photographer can check the depth of field displayed on the viewfinder, and can easily adjust the depth of field by adjusting the ND filter and the aperture.
JP 2002-196228 A JP 2003-319246 A

  However, in the conventional configuration described above, displaying the depth of field on the viewfinder has an effect of facilitating taking a picture intended by the photographer, but the subject determined by the size of the imaging device is effective. It is impossible to create images that exceed the limits of depth of field.

  The present invention solves the above-described conventional problems, and provides an imaging apparatus capable of capturing an image with a shallower depth of field than the limit of the depth of field determined by the size of the imaging device. The purpose is to do.

  The invention according to claim 1 of the present invention is an image sensor section that converts light information incident from a lens into electric charge, and a distance that measures the distance between the subject and the image sensor section for each of a plurality of regions of the image sensor section. A sensor unit; a lens control unit that performs focus control of the lens; and a calculation unit. In the calculation unit, from the distance information from the distance sensor unit and the focus distance information from the lens control unit, the imaging element unit The low-pass filtering process is performed on the video signal from the video signal, and an image having a shallow depth of field can be realized.

  According to a second aspect of the present invention, in the calculation unit, the characteristic of the low-pass filtering process is changed in accordance with an absolute value of a difference between distance information from the distance sensor unit and focus distance information. And has an effect that an image with a shallow depth of field can be realized.

  According to a third aspect of the present invention, the arithmetic unit performs low-pass filtering on the distance information from the distance sensor unit, and suppresses flickering of an image near the boundary of the subject. Has an effect.

  As described above, the present invention solves the above-described conventional problems, and can capture an image with a shallow depth of field more than the limit depth of field determined by the size of the image sensor. An excellent effect is obtained.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

(Embodiment 1)
FIG. 1 shows a configuration diagram of an imaging apparatus according to an embodiment of the present invention.

  In FIG. 1, 1 is a lens, 2 is a prism group that splits incident light from the lens 1 into R, G, and B wavelength components, 3 is an R-channel image sensor unit, 4 is a G-channel image sensor unit, 5 is an image sensor unit for B channel, 6 is an AD converter that converts video signals from the image sensor units 3, 4, and 5 into digital signals, 7 is a distance sensor unit that measures the distance to the subject, and 8 is a distance sensor unit. An AD converter that converts distance information from 7 into a digital signal, 9 is a control unit that performs lens control, distance sensor control, and the like, and 10 is a calculation unit.

  The light collected through the lens 1 is split into R, G, and B by the prism group 2, and the split light is sent to the image sensor sections 3, 4, and 5 for each channel. The image sensor units 3, 4, and 5 photoelectrically convert light information from the prism group 2 into charge information and output an analog video signal.

  The control unit 9 performs lens control such as focus, aperture, and zoom. Here, the relationship between the angle of view and the zoom will be described with reference to FIG. The angle of view represents the range that can be captured within the determined image size, expressed as an angle. If the horizontal image size is X, the vertical image size is Y, and the focal length is f, the horizontal angle of view. WH and vertical angle of view WV are expressed by the following equations.

  In a zoom lens, the angle of view can be changed by changing the focal length by zooming. FIG. 3 shows an image diagram of the focal length f and the angle of view. That is, when the focal length f is large, the angle of view becomes small. Conversely, when the focal length f is small, the angle of view becomes large.

  The control unit 9 controls the lens 1 and simultaneously sends the focal length f sent to the lens 1 to the distance sensor unit 7. The operation of the distance sensor unit 7 will be described with reference to FIG. The center point of the distance sensor unit 7 is attached to the camera so as to be the same as the center point C of the lens 1, and the horizontal field angle WH and the vertical field angle determined by (Equation 4) and (Equation 5). Sensing WV area (sensing area control). That is, the same area as the video area shown in FIG. 3 is sensed. That is, if the focal length is small, a wider range is sensed, and the sensing range is controlled to be narrowed as the focal length is increased. This makes it possible to measure the distance in the same range as the video area at any magnification. The distance sensor unit 7 measures the distance for each pixel of the CCD. For example, in the case of a CCD with 300,000 pixels, 300,000 pieces of distance data are measured. Further, the distance may be measured by a method as shown in FIG. In FIG. 5, the image sensor is provided with a distance sensor function. Each pixel includes a light receiving unit and a distance sensor unit, and distance measurement for each pixel is possible.

  As shown in FIG. 6, if a subject is a person at a distance of 3 m from the lens, a tree is at a distance of 6 m, and the sun is at ∞, the output of the distance sensor unit 7 is as shown in FIG. The distance (pixels indicated by diagonal lines) constituting the person is 3 m, the tree portion is 6 m, and the sun portion is ∞.

  Further, the control unit 9 sends the focus distance read from the lens 1 to the calculation unit 10. The focus distance is the distance from the in-focus lens to the subject. For example, in the case of FIG. 6, the focus distance when the focus is controlled so that the person is in focus is 3 m.

  Next, the process of the calculating part 10 is demonstrated using FIG. The calculation unit 10 receives the video signals R, G, and B, and the focus distance from the control unit 9 and the measurement distance for each pixel measured by the distance sensor unit 7. Here, the focus distance is L, and the measurement distance of the pixel n is Dn.

  First, LPDn is obtained by performing horizontal and vertical two-dimensional low-pass filtering on the measurement distance Dn. This eliminates high-frequency components near the boundary of the subject, thereby changing the characteristics of low-pass filtering applied to the video signal, which will be selected later, to some extent and suppressing flickering of the image near the boundary. It is.

  Thereafter, the absolute value of the difference between LPDn and the focus distance L is calculated, and the low-pass filtering characteristic applied to the video signal is changed according to the result. FIG. 9 shows the relationship between the absolute value and the characteristics of the selected low-pass filter. When the LPDn and the focus distance L are long, that is, when the absolute value is large, a low-pass filter characteristic with a narrow band as shown in FIG. 10A is selected to increase the effect of blurring the image. On the contrary, when LPDn and the focus distance L are short, that is, when the absolute value is small, as shown in FIG. 10b, the band of the low-pass filter to be selected is widened to reduce the blurring effect. In other words, since the image farther from the focus distance is subjected to the low-pass filter processing with a narrower band, the image region far from the focus distance becomes a low-frequency component, that is, a blurred image.

The process is summarized as follows.
Step 1 (S1)
Input step 2 (S2) of video signals R, G, B, measurement distance Dn of each pixel, and focus distance L
A horizontal and vertical two-dimensional low-pass filtering process is performed on the measurement distance Dn of each pixel to obtain LPDn.

LPDn = LPF (Dn)
LPF is an arbitrary function that performs a two-dimensional low-pass filtering process.
Step 3 (S3)
| L-LPnn | is calculated, and the low-pass filter characteristic is selected.
Step 4 (S4)
Low-pass filtering processing is performed on the video signals R, G, and B.

  As described above, the distance sensor unit 7 measures the distance for each pixel, and changes the characteristics of the low-pass filter adapted to the image according to the absolute value of the difference between the measured distance information and the focus distance, thereby artificially covering the pixel. An image with a shallow depth of field can be obtained.

  The imaging apparatus according to the present invention is useful for applications such as camera image processing that requires a shallow depth of field.

1 is a configuration diagram of an imaging apparatus according to an embodiment of the present invention. Illustration of camera angle of view Image of the relationship between focal length and angle of view The figure which shows the operation | movement range of the distance sensor in one embodiment of this invention The figure which shows the example of 1 structure of the distance sensor in one embodiment of this invention A diagram showing an example of a subject The figure which shows the output of the distance sensor in one embodiment of this invention The flowchart of the arithmetic processing in one embodiment of this invention The figure which shows the low-pass filter characteristic selection method in one embodiment of this invention The figure which shows the low-pass filter characteristic in one embodiment of this invention A diagram showing an example of a subject Illustration of depth of field

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens 2 Prism group 3 R channel image sensor part 4 G channel image sensor part 5 B channel image sensor part 6 AD converter 7 Distance sensor part 8 AD converter 9 Control part 10 Calculation part

Claims (3)

An image sensor unit that converts light information incident from the lens into electric charges, a distance sensor unit that measures the distance between the subject and the image sensor unit for each of a plurality of regions of the image sensor unit, and lens control that performs lens focus control A low-pass filtering process on the video signal from the imaging element unit based on distance information from the distance sensor unit and focus distance information from the lens control unit. An imaging device that is characterized. The imaging apparatus according to claim 1, wherein the calculation unit changes characteristics of the low-pass filtering process in accordance with an absolute value of a difference between distance information from the distance sensor unit and focus distance information. The imaging apparatus according to claim 1, wherein the arithmetic unit performs low-pass filtering processing on distance information from the distance sensor unit.

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