JP5121498B2 - Imaging apparatus and image data correction method - Google Patents

Description

  The present invention relates to an imaging device and a method for correcting image data, and more particularly to an imaging device for correcting chromatic aberration of an image and a method for correcting image data.

  In recent years, digital cameras and digital video cameras have become widespread due to technological innovation and price reduction. In these products, a subject is imaged by a lens system on an image sensor. The lens system uses light refraction by optical glass, but because the refractive index differs for each wavelength of light, the focal position for each wavelength moves back and forth, and the phenomenon of chromatic aberration that causes light dispersion is known, This contributes to the deterioration of image quality.

  Therefore, it is known to correct chromatic aberration by a method such as combining lenses having different dispersions. However, the number of lenses is limited due to the miniaturization of the camera, the lens material is limited due to the low cost, and further, the zoom magnification is also helped, making it difficult to optically correct chromatic aberration. It is coming.

  As described above, when it is difficult to correct chromatic aberration, which is a cause of image quality deterioration, using only the lens system, it is corrected by image processing. For example, Patent Document 1 stores correction data according to information on lens characteristics, zoom position, focus position, and distance from a center line that divides an image into left and right, and differs depending on the pixel area according to this data. A configuration for performing image processing is disclosed.

JP 2002-359771 A

  However, according to the configuration described in Patent Document 1, it is possible to compensate for chromatic aberration, but it is necessary to store in advance detailed information for specifying a pixel region. In addition, if color correction with a different degree is performed at a position where chromatic aberration occurs, it may be considered that an unnatural image is obtained.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce chromatic aberration in an imaging apparatus by a simple method without incurring costs.

In order to achieve the above object, an image pickup apparatus of the present invention includes a zoom lens, an image sensor that receives a subject image incident through the zoom lens, and converts the image into image data of each pixel including an electrical signal ; wherein in the image data, the saturation of image data located in a specific range of hue and saturation in the color space, in accordance with the correction amount which is determined on the basis of the hue and saturation of the image data, the color reduction correction And the specific hue and saturation range changes in hue range according to the zoom magnification of the zoom lens, and the correction amount does not depend on the pixel position of the image data in the image. The zoom lens changes according to the zoom magnification of the zoom lens .

Further, the correction method of the present invention for image data obtained by an imaging device having a zoom lens and an image sensor that receives a subject image incident through the zoom lens and converts the received image into image data composed of an electrical signal . wherein in the image data, the saturation of image data located in a specific range of hue and saturation in the color space, in accordance with the correction amount which is determined on the basis of the hue and saturation of the image data, the color reduction correction The specific hue and saturation range, the hue range changes according to the zoom magnification of the zoom lens, and the correction amount does not depend on the pixel position of the image data in the image , It changes according to the zoom magnification of the zoom lens .

  According to the present invention, it is possible to reduce chromatic aberration with a simple configuration without cost.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

(Device configuration)
FIG. 2 is a block diagram schematically showing an imaging system in an imaging apparatus such as a digital camera according to the embodiment of the present invention.

  In the figure, reference numeral 201 denotes a taking lens group. In the figure, a single convex lens is shown for the sake of convenience, but in actuality, it is composed of a plurality of lenses such as a focus lens and a zoom lens. Then, by driving these lenses, a magnification function (zoom function) for changing the magnification of the subject image formed on the image sensor 204 and a focus adjustment function (autofocus function) for adjusting the focus state of the subject image ) Etc. can be achieved. Reference numeral 202 denotes an aperture having a shutter function for adjusting the amount of light reaching the image sensor 204 and shielding the image sensor 204. By closing the aperture 202 after the image sensor 204 starts accumulating charges during still image shooting. The exposure time can be adjusted. An imaging control unit 203 controls the zoom function and focus function of the photographing lens group 201 and the light amount adjustment function and light shielding function of the aperture 202.

  Reference numeral 204 denotes an image sensor that is composed of a CCD or CMOS sensor and converts the received subject image into image data for each pixel composed of electrical signals. A pre-processing circuit 205 includes a CDS (correlated double sampling) circuit, an AGC (automatic gain control) circuit, and an A / D converter. Reference numeral 206 denotes a timing generator (TG) for generating signals for controlling the driving timing of the image sensor 204 and the preprocessing circuit 205 and controlling them.

  Reference numeral 207 denotes a signal processing circuit. As a part of a plurality of signal processing, the first color correction circuit 220 and the first color correction circuit 220 correct the saturation at a preset ratio with respect to the saturation in different ranges of hue. A two-color correction circuit 221. Therefore, in the present embodiment, saturation correction can be performed separately on image signals of two hues. The saturation correction will be described later in detail.

  A system control unit 208 controls the entire imaging apparatus. An image input / output control unit 209 controls transmission / reception of image data to / from the display unit 212 and the storage medium 210 described later. The storage medium 210 is a storage medium that stores image data processed by the signal processing circuit 207, and includes, for example, a DV tape, a DVD disk, a memory card, and the like. A display unit 212 such as a liquid crystal display or an organic EL display displays an image based on the image data processed by the signal processing circuit 207. Reference numeral 213 denotes an imaging switch for starting photographing, and 222 denotes a color temperature measuring element.

  The light incident on the photographic lens group 201 is adjusted so as to achieve proper exposure by controlling the diaphragm 202 by the imaging control unit 203, and is photoelectrically converted by the imaging element 204. The image data photoelectrically converted by the image sensor 204 is subjected to noise removal and gain control in the preprocessing circuit 205, and further A / D converted. Next, signal processing such as luminance correction, white balance processing, and digital effect processing such as fading is performed on the digital image data sent from the preprocessing circuit 205 in the signal processing circuit 207, and the image input / output control unit 209 is processed. send.

  The image input / output control unit 209 encodes the image data sent from the signal processing circuit 207 into JPEG format for still image data, MPEG format or the like for moving image data, and records it in the storage medium 210. To do. Further, when displaying the image data on the display unit 212, the image input / output control unit 209 performs signal processing for converting the image data into a format suitable for display on the display unit 212. Furthermore, image data can be read from the storage medium 210, decoded, converted into a format suitable for display, and output to the display unit 212.

(Example of chromatic aberration)
FIG. 1 is a diagram showing an example of chromatic aberration of the taking lens group 201. FIG. Since chromatic aberration has different characteristics depending on the lens, it is desirable to experimentally determine for each lens. The correction of chromatic aberration described in this embodiment can be applied to a lens having characteristics different from those shown in FIG. 1 by changing the correction parameter as long as the lens generates chromatic aberration.

  In FIG. 1, as an example of chromatic aberration, a total of 12 spot diagrams are shown, with 4 zoom ranges (zoom magnification) horizontally and 3 wavelengths vertically. Each spot diagram shows an imaging state of incident light at a specific point on the image sensor 204. The Y axis indicates the image height direction, and the Z axis indicates the direction orthogonal to the image height. In this embodiment, it is assumed that the photographing lens group 201 is a 12 × zoom lens, and FIG. 1 shows chromatic aberration at the wide angle end, 8 ×, 10 ×, and 12 × (telephoto end). Further, chromatic aberrations at wavelengths of 656 nm (red: R), 546 nm (green: G), and 436 nm (blue: B) are shown.

  In the example of the lens shown in FIG. 1, the aberration increases from 8 times the zoom range, and becomes maximum at 12 times. For this reason, in this embodiment, correction is not performed in the zoom range from wide angle to 8 times, but correction of chromatic aberration is performed only in the zoom range from 8 times to 12 times.

  Further, it can be seen that the chromatic aberration is large mainly in the vicinity of 436 nm (B) and 656 nm (R) compared with the wavelength of 546 nm (G). This shows that chromatic aberration occurs near 656 nm (R) for a subject with a low color temperature and near 436 nm (B) for a subject with a high color temperature. Furthermore, chromatic aberrations with both wavelengths of 436 nm (B) and 656 nm (R) occur in a subject that contains both of the same spectrum, so purple chromatic aberration occurs, and this color must be made inconspicuous. Can understand. Accordingly, in the present invention, 436 nm (B), 656 nm (R), and a mixture of both are corrected.

  Since the characteristics differ depending on the lens, the zoom range and hue for correcting the chromatic aberration may be appropriately determined for each lens.

(Color correction method)
3, 4, and 5 are diagrams for explaining correction parameters for chromatic aberration when the zoom lens of the photographing lens group 201 is in a 10 × zoom range.

  FIG. 3 shows a color space in which the horizontal axis is BY and the vertical axis is RY. FIG. 3 shows a color space with luminance values at which saturation can take the maximum value. An area 301 is a main correction area of the first color correction circuit 220, and an area 302 is a correction area for smoothly connecting the area 301 and an uncorrected area. The range of the region 301 shown in FIG. 3 is a range in which the saturation is medium from blue that is 30 degrees apart to magenta with the BY axis as the center. This correction area is set as a correction target by repeating measurement and experiment, and changes depending on the characteristics of the lens used for the photographing lens group 201.

  FIG. 4 is a graph showing the relationship between the correction amount and the saturation in the example shown in FIG. The correction amount is 0 in the saturation correction range shown in FIG. 3, that is, in the region outside the region 302, and the maximum correction amount in the region 301. In the area 302, the correction amount applied from the area 301 to the area outside the area 302 is linearly connected so that the correction is gradually applied. The correction range cannot be calculated directly from the wavelength to be corrected in the same way as the hue, but was set as shown in the figure by repeated measurement and experiment.

  FIG. 5 is a graph showing the relationship between the correction amount and the hue. In the region outside the hue region 302 shown in FIG. 3, the correction amount is 0, and in the region 301, the correction amount is the maximum in the correction region. In the region 302, the respective correction amounts are connected linearly so that correction is gradually applied.

  When the correction amount is determined as shown in FIGS. 4 and 5, the saturation of the signal is lowered by the determined correction amount. In the case of lowering the saturation, for example, when the input image data is at the position indicated by the point a in the area 301 as shown in FIG. 3, the direction is toward the origin so that the value indicated by the point a ′ is obtained. To lower the value.

  FIG. 6 shows an example of the correction range when the zoom lens of the photographic lens group 201 is at the telephoto end in the RY and BY color spaces. As an example, the zoom lens of the photographing lens group 201 increases chromatic aberration at the telephoto end, and increases chromatic aberration in the blue (B) direction. In order to cope with the deviation of the chromatic aberration, the correction region in FIG. 6 extends in the blue (B) direction, and is about 30 degrees toward the positive direction of RY about the BY axis. It is a region opened 60 degrees from the negative direction.

  In FIG. 6, an area 601 is the main correction area of the first color correction circuit 220, and an area 602 is a correction area for smoothly connecting the area 601 and the uncorrected area, which are defined by the hue and saturation ranges, respectively. ing. Although not described here, as in FIGS. 4 and 5, in hue and saturation, the correction amount of the region representing the region 601 is maximized, and the correction amount of the region representing the region 602 is the correction amount of the region 601. It is assumed that the correction amount 0 is linearly connected so that the correction is gradually applied.

  As an example of the imaging apparatus according to the present embodiment, when an imaging apparatus capable of moving image shooting, zooming may be performed during moving image shooting. If there are steps in the correction area and the correction amount due to changes in the zoom area, As a result, the image quality deteriorates.

  The graph of FIG. 7 represents a change in the correction amount according to the zoom range. In the present embodiment, the saturation of a color located in a specific hue and saturation range in the color space shown in FIG. 3 according to the position of the zoom lens does not depend on the coordinates of the image data in the image. Correction to reduce uniformly. As described above, the taking lens group 201 is an example of a lens system in which the chromatic aberration increases from around 8 times in the zoom range. Therefore, the correction amount is increased from 8 times to maximize the correction amount at the telephoto end. The amount of chromatic aberration increases linearly and is linearly connected so that the correction amount smoothly shifts for moving image quality. In the present embodiment, the maximum correction amount is set to 25%. This indicates that the saturation is reduced by 25% with respect to the image before the correction is performed in the case where the correction is most performed.

  With reference to the correction amount shown in FIG. 7, the correction amount changes as shown in the graphs of FIGS. 4 and 5 in accordance with the hue and saturation. That is, the saturation is reduced by 25% for the color in the zoom region at the telephoto end (12 times) and located in the region 601 shown in FIG. For the color located in the zoom range at the telephoto end and in the region 602 shown in FIG. 6, the saturation is reduced in the range of 0 to 25% according to the hue and saturation. Also, the saturation is reduced by 12.5% for colors located in the area 301 shown in FIG. For a color whose zoom area is 10 times and which is located in the area 302 shown in FIG. 3, the saturation is reduced in the range of 0 to 12.5% according to the hue and saturation.

  The graph of FIG. 8 represents the change in the hue of the correction area according to the zoom area. When the photographic lens group 201 in the present embodiment is used, as seen from the comparison between the correction range when the zoom range shown in FIG. 3 is 10 times and the correction range at the telephoto end shown in FIG. 6, it approaches the telephoto end. The hue that is the target of chromatic aberration increases in the blue (B) direction. Furthermore, the hue area to be corrected becomes wider. Therefore, as shown in FIG. 8, it is necessary to shift the correction start hue in the blue (B) direction as it approaches the telephoto end, and linearly connected so that the correction amount smoothly shifts for moving image quality.

  FIGS. 9 and 10 are graphs of changes in the correction amount and the correction range depending on the color temperature in the first color correction circuit 220 whose correction target is blue (B).

  FIG. 9 is a graph showing changes in the correction amount depending on the color temperature. The lower the color temperature of the subject, the smaller the blue (B) component included in the image data, and the higher the color temperature, the greater the blue (B) component included in the image data. Therefore, the correction amount is smoothly increased for a subject with a high color temperature.

  FIG. 10 shows the start hue and end hue of the correction range based on the color temperature. As described above, since the ratio of the color components included in the image data changes depending on the color temperature, the color that appears as chromatic aberration may also change, so the start hue and end hue that define the correction area are smoothly set according to the color temperature. Change. Here, the hue to be corrected shifts to the blue (B) side as the color temperature increases. On the other hand, in the second color correction circuit 221 for correcting red (R), it is desirable to increase the correction amount and shift the hue to the red (R) side as the color temperature of the subject is lower.

  The color temperature in FIGS. 9 and 10 may be replaced with a ratio of R and B spectral integration values obtained by decomposing a signal imaged by the image sensor 204 into color signals such as RGB. Alternatively, the color temperature measuring element 222 may be provided to measure directly from outside light.

  FIG. 11 shows an example of a color correction range performed when the luminance of an image is higher than a preset luminance, such as when the luminance is saturated, in RY and BY color spaces. An area 1101 and an area 1102 are blue (B) color correction ranges to be corrected by the first color correction circuit 220, and an area 1103 and an area 1104 are color correction ranges to be corrected by the second color correction circuit 221. . Also in these areas, the range of hue and saturation to be corrected is defined by experimentally determining the characteristics of the photographic lens group used. That is, the first color correction circuit 220 performs correction in each zoom area, such as data indicating the hue and saturation ranges of the correction areas shown in FIGS. 3 and 6 and data indicating the areas 1101 and 1102 of FIG. It has data indicating the area. Then, it is determined whether the image data incident from the preprocessing circuit 205 is within these ranges. Similarly, the second color correction circuit 221 has data indicating a correction area in each zoom area, and determines whether the image data incident from the preprocessing circuit 205 is within these ranges. When it is determined that the image data is in one of the correction area ranges held by the first color correction circuit 220 or the second color correction circuit 221, the saturation is increased by the above-described method by the corresponding correction circuit. It is corrected.

  FIG. 12 shows an example in which an image is displayed as a histogram by luminance and the number of pixels. The image acquired by the image sensor 204 may be a histogram as shown in the figure, and may be determined to be higher than the preset brightness when the ratio of the high brightness component is higher than the preset threshold. This luminance detection may be performed by the signal processing circuit 207 or may be performed by the system control unit 208 as part of exposure control for controlling the aperture 202.

  As for the detection of luminance, another element for measuring the luminance of external light may be separately provided and detected, or an element with high sensitivity for high luminance may be prepared for the image sensor 204. If every 60 frames are acceptable as in the case of moving image shooting, the shutter speed should be faster than 1/60 when the luminance is high, and the luminance may be measured with a high-speed shutter between frames.

FIG. 13 shows an example of the maximum correction amount by luminance. The chromatic aberration around the red (R) is conspicuous only when the luminance is saturated, so that correction is performed only at high luminance. In other words, only at the time of high luminance exceeding the luminance L _H, the second color correction circuit 221 is used, amount corresponding to the correction amount shown in FIG. 13, lower the saturation.

  Note that the correction at high luminance around the red (R), like the correction around the blue (B), smoothly switches between a portion to be corrected by hue and saturation (region 1103 in FIG. 11) and a portion not to be corrected. (Region 1104 in FIG. 11). Further, the correction amount may be changed depending on the zoom magnification, or the correction amount may be changed depending on the color temperature.

  As described above, according to the embodiment of the present invention, the saturation of a color located in a specific hue and saturation range is uniformly applied to the entire image according to the zoom state of the photographing lens group 201. Process to reduce. As a result, it is not necessary to change the correction amount in accordance with the coordinates of the image data as in the prior art, so that it is possible to reduce chromatic aberration by a simpler method without incurring costs.

It is a figure which shows an example of the chromatic aberration of the imaging lens group in embodiment of this invention. 1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows the correction range in case the zoom area in embodiment of this invention is 10 times. It is a figure which shows the corrected amount with respect to the saturation method in case the zoom area in embodiment of this invention is 10 times. It is a figure which shows the corrected amount with respect to a hue in case the zoom area in embodiment of this invention is 10 times. It is a figure which shows the correction | amendment range in case the zoom lens in embodiment of this invention exists in a telephoto end. It is a figure which shows the corrected amount according to the magnification of the zoom lens in embodiment of this invention. It is a figure which shows the range of the hue corrected according to the zoom magnification in embodiment of this invention. It is a figure which shows the corrected amount according to the color temperature in embodiment of this invention. It is a figure which shows the change of the range of the hue to correct | amend according to the color temperature in embodiment of this invention. It is a figure which shows the correction range at the time of the brightness | luminance saturation in embodiment of this invention. It is a histogram which shows the luminance distribution of the image at the time of the luminance saturation in embodiment of this invention. It is a figure which shows the corrected amount according to the brightness | luminance in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 201 Shooting lens group 202 Diaphragm 203 Image pick-up control part 204 Image pick-up element 205 Pre-processing circuit 206 Timing generator (TG)
207 Signal Processing Circuit 208 System Control Unit 209 Image Input / Output Control Unit 210 Storage Medium 212 Display Unit 213 Imaging Switch 220 First Color Correction Circuit 221 Second Color Correction Circuit

Claims (8)

A zoom lens,
An image sensor that receives a subject image incident through the zoom lens and converts the image into image data of each pixel including an electrical signal ;
Wherein in the image data, the saturation of image data located in a specific range of hue and saturation in the color space, in accordance with the correction amount which is determined on the basis of the hue and saturation of the image data, the color reduction correction Means,
The specific hue and saturation range varies depending on the zoom magnification of the zoom lens,
The imaging apparatus according to claim 1, wherein the correction amount does not depend on a pixel position of image data in an image and changes according to a zoom magnification of the zoom lens . The correction amount maximum value of the higher zoom magnification of the zoom lens, an imaging apparatus according to claim 1, wherein the high rather Rukoto. Range of the hue, as the zoom magnification before Symbol zoom lens is high, the imaging apparatus according to claim 1 or 2, characterized in that Naru widely. A measuring means for measuring the color temperature of the subject;
The correction amount, the higher the color temperature of the object is high, the imaging apparatus according to any one of claims 1 to 3, characterized in that increase. A measuring means for measuring the color temperature of the subject;
Range of the hue, as the color temperature of the object is high, the imaging apparatus according to any one of claims 1 to 4, characterized in shift toss isosamples toward the red side to blue side. The color correction means 1 through claim, characterized in including that a plurality of color correction circuit for reducing chroma of each of the image data located in a range of different specific hue and chroma from each other in the color space The imaging device according to any one of 5. A luminance detecting means for detecting the luminance of the subject;
The color correction unit reduces the saturation of the image data located in the specific hue and saturation range in a color space if the luminance detected by the luminance detection unit is higher than a preset luminance. the imaging apparatus according to claim 1 to 6, wherein. A method for correcting image data obtained by an imaging device having a zoom lens and an imaging device that receives a subject image incident through the zoom lens and converts the received subject image into image data including an electrical signal ,
Wherein in the image data, the saturation of image data located in a specific range of hue and saturation in the color space, in accordance with the correction amount which is determined on the basis of the hue and saturation of the image data, the color reduction correction Having a process,
The specific hue and saturation range varies depending on the zoom magnification of the zoom lens,
The method of correcting image data, wherein the correction amount does not depend on a pixel position of the image data in the image and changes according to a zoom magnification of the zoom lens .

Images