JP2003333381A - Imaging apparatus with image evaluation function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus for evaluating image quality of a photographed image, discriminating right and wrong of the photographed image and capable of showing the result to a photographer. <P>SOLUTION: An image evaluation arithmetic circuit 20 receives a signal resulting from RAW data subjected to YUV conversion at a YUV conversion processing section 18 in an image data controller 6, and a histogram generating section 21 receiving the signal generates a histogram from a luminance signal (Y). An image evaluation section 22 evaluates the image quality of the photographed image as to exposure and contrast of the photographed image from the generated histogram and outputs the evaluation result to an image display apparatus 8 and an image recording medium 10. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to capturing and / or capturing electronic images.
The present invention relates to an image pickup apparatus with an image evaluation function applied to a reproducing digital camera or the like.

[0002]

2. Description of the Related Art FIG. 10 is a block diagram showing an example of the configuration of a general digital camera. An optical signal obtained from a subject is condensed on an image pickup element 2 by an optical lens 1.
Photodiodes are regularly arrayed in the image sensor 2,
Vertical CCD (charge coupled device: Charge C) as charge transfer path
There is an coupled device) and a horizontal CCD, and the photoelectric conversion function of the photodiode accumulates electric charges according to the amount of incident light and converts an optical signal into an electric signal. The amount of light incident on the image sensor 2 can be adjusted by the mechanical shutter 3 in front of the image sensor 2 and the electronic shutter inside the image sensor 2. One photodiode corresponds to one pixel, and generally R (Re
One of the color filters of d), G (Green) and B (Blue) is attached.

The signal output from the image pickup device 2 is S / H.
The data is input to the (Sample / Hold) circuit 4, sample-held, and data corresponding to each pixel is extracted. A / D
The (Analog / Digital) circuit 5 converts the analog signal from the S / H circuit 4 into a digital signal. A / D circuit 5
The data output from is simply referred to as the "RAW data" because the information from the image sensor 2 is extracted. A
The signal from the / D circuit 5 is input to the image data controller 6 and image processing is performed. The DRAM 7 is used as a temporary storage location for data during image processing. The processing content of the image data controller 6 will be described with reference to FIG. 11 described later. The image display device 8 displays the image during or after the signal conversion of the imaged image for the display device.

The image compression circuit 9 converts the image data into JPE.
The data is compressed / decompressed in conformity with a format standard such as G, and then stored in the image recording medium (smart media, compact flash (registered trademark), etc.) 10.
EEPROM (electrically erasable and programmable RO
M) 11 stores a program or data for operating the apparatus optimally. The system controller 12 reads out data from the EEPROM 11 in accordance with a signal obtained from the operation switch 13 or the like and controls the system. Here, the operation switch 13 includes a release switch, a power switch, a switch for switching a shooting / playback mode, and the like. Timing generator 14
Controls the operation timing of the image sensor 2, the S / H circuit 4, the A / D circuit 5, and the image data controller 6.
The shutter drive circuit 15 controls the operation of the mechanical shutter 3.

FIG. 11 is a block diagram showing a flow of image processing in the general digital camera described in FIG. 10. RAW data output from the A / D circuit 5 in FIG. When input, the RGB interpolation processing unit 16 first performs RGB interpolation.
At the stage of RAW data, since the color filter is attached to the photodiode, only one color of R, G, and B is held for one pixel. Therefore, the RGB interpolation processing unit 16 interpolates the remaining two colors. Next, the gamma correction processing unit 17 performs gamma correction to adjust the tone (gradation) of the image, and the YUV conversion processing unit 18 converts the RGB signal into a luminance signal (Y) and a color difference signal (U, V). In addition to this, there is a method in which the edge portion of the image is processed to enhance the edge of the image.

[0006]

In recent years, due to the widespread use of electronic image pickup devices such as digital cameras having the above-mentioned structure, it is possible to confirm the image on the spot after shooting, and image processing and printer output by loading the shot image into a personal computer. It has become possible for general users to easily handle captured images.

However, since there is no conventional image pickup apparatus having a function of judging the quality of a photographed image, the photographer cannot find a point to be satisfied with the photographed image.

On the other hand, Japanese Patent Laid-Open No. 2001-167253
Japanese Patent Laid-Open Publication proposes that position information of a subject is acquired from a captured image and the result of comparison with predetermined composition data is output as an image evaluation. This is only a proposal for composition evaluation of a photographed image, and it cannot be said that it is a comprehensive evaluation of images because of lack of specific evaluation elements such as exposure and contrast. Further, as the size of the image pickup device is reduced, the image display device provided in the image pickup device is generally small, which makes it difficult to check detailed information.

An object of the present invention is to solve the above-mentioned conventional problems, evaluate the image quality of a photographed image, judge whether the photographed image is good or bad, and show the result to the photographer. To provide a device.

[0010]

In order to achieve the above-mentioned object, the invention according to claim 1 is an evaluation element extraction means for extracting an image quality evaluation element from a photographed image, and a frequency based on the extracted image quality evaluation element. It is provided with a histogram creating means for creating a histogram representing a distribution, an image quality evaluating means for evaluating the image quality of a captured image based on the histogram, and an evaluation result outputting means for outputting an evaluation result in the image quality evaluating means. With this configuration, the photographed image can be evaluated using a histogram, and the evaluation result can be displayed and output so that the photographer can easily judge the quality of the photographed image on the spot after the photographing. You can In addition, by using the evaluation result as a criterion and performing the shooting again on the spot, the frequency of shooting failures can be reduced and the image intended by the photographer can be obtained.

According to a second aspect of the present invention, in the image pickup apparatus with the image evaluation function according to the first aspect, the image quality evaluation means comprises:
It is characterized by comprising a comparison means for comparing the information obtained from the histogram from the histogram creation means with a preset reference value, and a weighting means for weighting the evaluation based on the comparison result from this comparison means. With this configuration, the photographer can obtain an objective evaluation of the image captured by himself / herself by comparing and evaluating the captured image with a preset reference value. By performing weighting, it is possible to operate the image file using the evaluation result as a parameter, and for example, it is possible to select the best one image from a plurality of images captured in the same landscape.

According to a third aspect of the present invention, in the image pickup apparatus with an image evaluation function according to the first or second aspect, a luminance signal is used as an image quality evaluation element, and a captured image is captured based on a histogram created for the luminance signal. Characterized by evaluating the exposure, with this configuration, by evaluating the exposure of the captured image using the histogram, and by outputting the evaluation result,
The photographer can immediately judge whether the exposure of the photographed image is good or bad after the photographing. In addition, it is possible to reduce shooting failures such as a low-exposure, dark part being crushed in black, and a high-exposure bright part being blown out in white, and it is possible to shoot with an appropriate exposure.

According to a fourth aspect of the present invention, in the image pickup apparatus with an image evaluation function according to the first or second aspect, a luminance signal is used as an image quality evaluation element, and a captured image is captured based on a histogram created for the luminance signal. This configuration is characterized by evaluating the contrast.By using this configuration, the contrast of the photographed image is evaluated using the histogram, and the evaluation result is output, so that the photographer can evaluate the contrast of the photographed image immediately after photographing. You can judge the evil. Further, since it is generally difficult to judge the quality of the image based on the contrast, the photographer can easily confirm the completion of the image based on this evaluation result.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. In the following description, members corresponding to those described with reference to FIGS. 10 and 11 are designated by the same reference numerals.

FIG. 1 is a block diagram showing a structure of a digital camera having a function of evaluating a photographed image for explaining an embodiment of the present invention. The structure of the conventional general digital camera described in FIG. Compared with the above, the difference is that the image evaluation calculation circuit 20 is added. In this embodiment,
The image evaluation calculation circuit 20 receives data from the image data controller 6, outputs data to the image display device 8 and the image recording medium 10, and temporarily stores data during calculation in a memory, for example, the DRAM 7. Do it.

In FIG. 1, an optical signal obtained from a subject is condensed by the optical lens 1 and imaged on the image pickup element 2,
It is converted into an electric signal by photoelectric conversion. Next, S / H
A signal corresponding to each pixel is extracted as analog data by the circuit 4, and analog / digital conversion is performed by the A / D circuit 5 to obtain digital data. This digital data is a signal obtained by extracting the signal input to the CCD of the image sensor 2 and is called “RAW data”. The RAW data is input to the image data controller 6 for image processing, and then input to the image evaluation calculation circuit 20 for image evaluation.

FIG. 2 is a block diagram showing the data flow from the RAW data in the image evaluation calculation circuit of this embodiment. When the RAW data is input to the image data controller 6, the RGB interpolation processing section 16 outputs R, R to each pixel.
Three colors G and B are given. Next, the gamma correction processing unit 17
The tone (gradation) of the image is adjusted by the YUV conversion processing unit 18, and the RGB signal is converted into a luminance signal (Y) and a color difference signal (U, V). In the image evaluation calculation circuit 20, the image data controller 6 is connected to the YUV conversion processing unit 1
The YUV converted signal is input at 8, and the histogram creating unit 21 creates a histogram (Histgram) for the luminance signal (Y). The image evaluation unit 22
Then, the image quality of the captured image is evaluated from the histogram for the exposure and contrast of the captured image, and the evaluation result is output to the image display device 8 and the image recording medium 10.

Here, in the image evaluation calculation circuit 20,
An example of evaluating the exposure of the captured image from the histogram created for the luminance signal (Y) in the captured image will be shown.

That is, in the photographed image, when the exposure is low, the dark portion tends to be blackened, and when the exposure is high, the bright portion tends to fly white. The digital camera has an advantage that the photographed image can be checked on the spot, but since the image display device 8 mounted is small, the exposure is low and the hair is crushed black, or the exposure is high and the sky is white. It is difficult to confirm information such as flying. Therefore, in this embodiment, by giving an evaluation to the exposure, it is possible to judge whether or not it is necessary to retake an image based on the evaluation result.

FIG. 3 shows an example of a histogram created from the luminance signal (Y). In the histogram, the horizontal axis represents the luminance value and the vertical axis represents the frequency. In order to evaluate the exposure of the captured image, it is only necessary to use a portion having a low luminance value and a portion having a high luminance value in the histogram. When the exposure is low, the frequency of the low luminance portion of the histogram is high, and when the exposure is high, the frequency of the high luminance portion of the histogram is high.

FIG. 4 shows a histogram when the exposure is low and the frequency of the low-luminance portion is high. As an example of the evaluation method when the exposure is low, a reference value (low brightness reference value) is set for the low brightness part, and the number of samples with a brightness value lower than the low brightness reference value is The evaluation point is whether or not it is a ratio.

For example, as shown in FIG. 5, a plurality of reference values are provided in advance for the above-mentioned ratio, and weighted points are defined between the reference values. Next, it is calculated which reference value range the captured image data is included in, and an evaluation point is given. In the case of FIG. 5, the point is 40.

FIG. 6 shows a histogram when the exposure is high and the frequency of the high-luminance portion is high. Similar to when the exposure is low, set the reference value (high-brightness reference value) for the high-brightness area, and set the number of samples with a brightness value higher than the high-brightness reference value to the total number of samples. Give evaluation points. The evaluation points of both the low-luminance side and the high-luminance side are added to make the total evaluation point for exposure.

Next, an example of evaluating the contrast of the photographed image from the histogram created for the luminance signal (Y) of the photographed image will be described. FIG. 7 shows a histogram when the contrast is low, and FIG. 8 shows a histogram when the contrast is high.

When the contrast is low, the distribution (dispersion) of the histogram is small, resulting in an image that is vague and non-tight as a whole. The image has a sharp contrast between black and white. However, as described above, in a digital camera or the like, an image display device is generally small, and it is not only difficult to check the contrast of a shot image after shooting, but also it is difficult to judge the quality of an image based on the contrast. . Therefore, by giving an evaluation to the contrast, the evaluation result can be used as a good or bad index. As an example of evaluating the contrast, there is a method of using the standard deviation of the data calculated from the histogram created for the luminance signal (Y) of the captured image.

For example, as shown in FIG. 9, a plurality of reference values are prepared in advance, and weighted points are defined between the reference values. Next, the standard deviation is calculated from the histogram, and an evaluation point is given according to which reference value range the data is included in, and the result is evaluated as the contrast. In the case of FIG. 9, the point is 50.

As described above, the evaluation points obtained from the exposure and the contrast are added and treated as a total evaluation point in the photographed image. It should be noted that the exposure and contrast evaluation reference values are not fixed in all situations, but may be changed depending on the shooting scene such as a night view, landscape, or portrait.

As an output example of the evaluation result obtained as described above, the evaluation points may be displayed on the image display device 8 as they are together with the photographed image, or the symbol evaluations may be ranked based on the evaluation points. You may display it. In addition, the evaluation result may be output by voice with a voice device,
If the evaluation point is low, a message requesting reshooting may be output. Also, an advice-like message may be output together with the evaluation result.

Further, by outputting the evaluation result to the image recording medium 10, it becomes possible to compare the evaluation result with the image previously photographed, and when the image is reproduced, the evaluation result is used as a parameter to retrieve or arrange the photographed images. If the capacity of the image recording medium 10 is insufficient, images having a low rating are automatically deleted.
Its usage range is wide.

In outputting the evaluation result to the image recording medium 10, the evaluation result may be stored in the image file, or a file for the evaluation result may be created separately, and the evaluation result and the photographed image are stored. The address may be stored in the file. In the former case, since the evaluation result is stored in the image file, the evaluation result can be referred to even if the device is changed. In the latter case, when file operation is performed based on the evaluation result, the file operation can be performed only by reading the evaluation result file, and it is not necessary to handle an image file with a large file size, resulting in a system load. Becomes lighter.

[0031]

As described above, according to the present invention,
By using the histogram to evaluate the image quality of the captured image and displaying the evaluation result and outputting the result, the photographer can easily determine the quality of the captured image on the spot after capturing. In addition, using the evaluation result as a criterion,
By retaking the shooting on the spot, the frequency of the shooting failures can be reduced, and the image intended by the photographer can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital camera having a function of evaluating a captured image for explaining an embodiment of the present invention.

FIG. 2 is a RAW in the image evaluation calculation circuit according to the present embodiment.
Block diagram showing data flow from data

FIG. 3 is a diagram showing an example of a histogram created from a luminance signal (Y) according to the present embodiment.

FIG. 4 is a diagram showing a histogram according to the present embodiment when the exposure is low and the frequency of low-luminance portions is high.

FIG. 5 is an explanatory diagram of evaluation points according to the present embodiment.

FIG. 6 is a diagram showing a histogram when the exposure is high and the frequency of a high-luminance portion is high according to the present embodiment.

FIG. 7 is a diagram showing a histogram when the contrast is low according to the present embodiment.

FIG. 8 is a diagram showing a histogram when the contrast according to the present embodiment is high.

FIG. 9 is an explanatory diagram of a method of using a standard deviation of data calculated from a histogram according to this embodiment.

FIG. 10 is a block diagram showing a configuration of an example of a conventional general digital camera.

11 is a block diagram showing a flow of image processing in the general digital camera described in FIG.

[Explanation of symbols]

6 Image data controller 7 DRAM 8 Image display device 9 Image compression circuit 10 image recording media 16 RGB interpolation processing unit 17 Gamma correction processor 18 YUV conversion processing unit 20 Image evaluation calculation circuit 21 Histogram creation section 22 Image Evaluation Department

Claims (4)

[Claims] 1. An evaluation element extraction means for extracting an image quality evaluation element from a captured image, a histogram creation means for creating a histogram representing a frequency distribution based on the extracted image quality evaluation element, and a captured image of the captured image based on the histogram. An image pickup apparatus with an image evaluation function, comprising: an image quality evaluation means for evaluating image quality; and an evaluation result output means for outputting an evaluation result by the image quality evaluation means. 2. The image quality evaluation means compares the information obtained from the histogram from the histogram creation means with a preset reference value, and weights the evaluation based on the comparison result from the comparison means. The image pickup apparatus with an image evaluation function according to claim 1, wherein the image pickup apparatus is composed of weighting means for performing. 3. The image pickup apparatus with an image evaluation function according to claim 1, wherein the brightness signal is used as an image quality evaluation element, and the exposure of the captured image is evaluated based on a histogram created for the brightness signal. . 4. The image pickup apparatus with an image evaluation function according to claim 1, wherein the brightness signal is used as an image quality evaluation element, and the contrast of the photographed image is evaluated based on a histogram created for the brightness signal. .