JP2000261719A - Image processing method, its system and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply image processing to image data so as to obtain an impression of brightness at photographing. SOLUTION: A digital camera 1 acquires image data S0 receiving AE processing and a luminance meter 6 measures luminance at photographing to obtain absolute luminance information K and they are recorded in a recording medium 2. A gradation processing means 8 in a lab 3 applies gradation processing to adjust the contrast of the image data S0 in a way that the contrast is more increased as the luminance at photographing is higher on the basis of the absolute luminance information K to obtain processed image data S1, and an output means 9 prints out the data S1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for performing image processing on image data obtained by photographing in consideration of luminance at the time of photographing, and a program for causing a computer to execute the image processing method. The present invention relates to a computer-readable recording medium having recorded therein.

[0002]

2. Description of the Related Art Digital image data obtained by a digital electronic still camera (hereinafter referred to as a digital camera) or digital image data obtained by reading an image recorded on a film can be converted into a hard copy such as a print or displayed. Above is being reproduced as a soft copy. As described above, when reproducing digital image data, it is expected to have the same high-quality image quality as a photograph printed from a negative film.

On the other hand, when recording image data obtained by a digital camera on a recording medium, photographing such as gamma characteristics of the camera, focal length of the lens, F-number of the lens, and the contents of AE processing performed in the camera are performed. A method of recording conditions on a recording medium has been proposed (Japanese Patent Laid-Open No. 10-1).
No. 91246). According to this method, when printing the image data, it is possible to perform processing for improving the image quality of the image data with reference to the photographing conditions recorded on the recording medium, thereby obtaining a print with a good finish. Can be.

In the case of a digital camera, the camera itself has an automatic exposure (AE) function.
Exposure correction processing is performed by adjusting the gradation and frequency characteristics of image data using the E function. When reading an image from a film, a similar exposure correction process is performed in a laboratory. By performing the exposure correction process in this manner, even in the case of a sunlit scene and a shaded scene in which the luminance at the time of shooting differs by 100 times, the image that is printed out becomes white or black. The scene at the time of shooting can be reproduced without becoming dull.

[0005]

By performing exposure correction processing using such an AE function, an image can be reproduced without any extreme change in brightness, regardless of the brightness of the scene. . However, since such an AE function performs an exposure correction process so as to have a uniform brightness regardless of the brightness of a captured scene,
For example, even in a very bright and crisp scene such as a midsummer sandy beach, the uniform exposure correction by the AE function impairs the crisp impression during shooting.

The present invention has been made in view of the above circumstances, and causes a computer to execute an image processing method and apparatus and an image processing method capable of performing image processing on image data without impairing the impression at the time of photographing. It is an object to provide a computer-readable recording medium on which a program for recording is recorded.

[0007]

An image processing method according to the present invention is directed to an image processing method for performing image processing on image data representing an image obtained by photographing, the image processing method comprising: And get
On the basis of the absolute luminance information, the image data is subjected to image processing for changing gradation and / or frequency characteristics to obtain processed image data.

In the image processing, the gradation and / or frequency of the image data is adjusted so that the image represented by the processed image data approaches the gradation and / or frequency characteristics perceived during photographing. Preferably, the process is for changing the characteristics.

Here, the "absolute luminance information" may be obtained by providing a luminance meter in a camera and measuring the luminance at the time of photographing with the luminance meter. The image data obtained by photographing is subjected to exposure correction. If not, it may be obtained from information such as image data and aperture value at the time of shooting. If the camera is a digital camera having a luminance meter, the absolute luminance information may be recorded on a recording medium for recording image data and passed to a laboratory for outputting the information. A so-called APS film capable of recording magnetic information may be used. In the case of a camera to be used, absolute brightness information may be recorded in a magnetic recording section of the APS film and passed to the laboratory. Further, the absolute luminance information K may be recorded on a recording medium such as an FD and transferred to a laboratory. In addition, the “absolute luminance information” includes not only a numerical value of the absolute luminance of the scene at the time of shooting, but also
As shown in Table 1 below, representative values of the range of the absolute luminance,
The range of the absolute luminance may be represented by a symbol.

[0010]

[Table 1]

An image processing apparatus according to the present invention is an image processing apparatus for performing image processing on image data representing an image acquired by photographing, wherein the luminance information acquiring unit acquires absolute luminance information relating to the absolute luminance of a scene at the time of photographing. Means, and processing means for performing image processing for changing gradation and / or frequency characteristics on the image data based on the absolute luminance information to obtain processed image data. It is.

[0012] The processing means may control the gradation and / or frequency of the image data so that the image represented by the processed image data approaches the gradation and / or frequency characteristics perceived during photographing. Preferably, it is a means for performing a process of changing characteristics.

[0013] The image processing method according to the present invention may be provided by being recorded on a computer-readable recording medium as a program for causing a computer to execute the method.

[0014]

According to the present invention, the processing for changing the gradation and / or frequency characteristics is performed on the image data based on the absolute luminance information relating to the absolute luminance of the scene at the time of photographing. It is possible to obtain processed image data representing an image reflecting the brightness of the scene of
By reproducing the processed image data, it is possible to obtain an image according to the luminance impression at the time of shooting.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing a configuration of an image output system to which an image processing device according to a first embodiment of the present invention is applied. As shown in FIG.
The image output system according to the embodiment stores the image data S0 acquired by the digital camera 1 on the recording medium 2
The recording medium 2 is transferred to the laboratory 3 and printed out there.

The digital camera 1 has a CCD, an optical system necessary for photographing, an image pickup means 4 having an autofocus function and the like.
An automatic exposure correction (AE) means 5 for performing an automatic exposure correction process on the original image data S 'obtained by the imaging means 4 to obtain image data S0, and a luminance meter for measuring the luminance of the scene at the time of shooting 6. The AE means 5 obtains image data S0 by correcting the exposure of the original image data S 'so that the image does not become white or black, regardless of the luminance of the scene at the time of shooting. Therefore, the image data S0 acquired by the digital camera 1 and recorded on the recording medium 2 has already been subjected to exposure correction. The measurement result of the luminance by the luminance meter 6 is recorded on the recording medium 2 as absolute luminance information K.

The recording medium 2 is a digital medium for recording image data S0 and absolute luminance information K such as a smart media, a compact flash, a memory stick, and the like.

The laboratory 3 reads out the image data S0 and the absolute luminance information K recorded on the recording medium 2, and adjusts the contrast of the image data S0 based on the absolute luminance information K to process the processed image data S1. And output means 9 such as a printer for printing out the processed image data S1.

The gradation processing means 8 adjusts the contrast of the image data S0 as follows. FIG. 2 is a graph showing the relationship between the luminance and the apparent brightness with respect to the luminance, and FIG. 3 is a graph showing only the portion showing the luminance contrast in FIG. As shown in FIG. 2, in a scene at the time of shooting, the higher the luminance is, the brighter the white thing looks and the darker the black thing looks. For this reason, as shown in FIG. 3, the contrast is low in a dark place such as indoors, and the contrast is high in a bright place such as outdoors in fine weather. Therefore, based on the absolute luminance information K at the time of photographing, the gradation processing means 8 increases the contrast when the absolute luminance is high, and lowers the contrast when the absolute luminance is low. The contrast of the data S0 is adjusted to obtain the processed image data S1. Note that the contrast in this case includes not only the gray contrast but also the contrast related to each of the RGB components. Further, the gradation processing unit 8 may perform a color conversion process in consideration of an observation light source for observing a print, a color reproduction range of the output unit 9, and the like.

Next, the operation of this embodiment will be described. FIG. 4 is a flowchart showing the operation of the first embodiment. First, photographing is performed by the digital camera 1 (step S1), and the original image data S 'obtained by photographing is taken.
Is subjected to exposure correction by the AE means 4 to obtain image data S0 (step S2). The luminance at the time of shooting is measured by the luminance meter (step S3), and the absolute luminance information K representing the luminance and the obtained image data S0 are recorded on the recording medium 2 (step S4). The above is the processing performed in the digital camera 1.

The recording medium 2 is transferred to the laboratory 3 and read by the reading means 7 with the absolute luminance information K and the image data S0.
Is read from the recording medium 2 (step S5).
Then, the gradation processing means 8 performs gradation processing for adjusting the contrast of the image data S0 based on the read absolute luminance information K, and obtains processed image data S1 (step S6). The processed image data S1 is printed out by the output means 9 (Step S
7), the process ends.

As described above, according to the present embodiment, the gradation processing for adjusting the contrast is performed on the image data based on the absolute luminance information K relating to the absolute luminance of the scene at the time of shooting. The higher the luminance of the image, the higher the contrast, and it is possible to obtain processed image data S1 representing an image reflecting the luminance of the scene at the time of shooting. Therefore, by reproducing the processed image data S1, it is possible to obtain an image according to the luminance impression at the time of shooting.

Next, a second embodiment of the present invention will be described. FIG. 5 is a schematic block diagram showing a configuration of an image output system to which the image processing device according to the second embodiment of the present invention is applied. In the second embodiment, the configuration of the digital camera 1 and the reading means 7 and the output means 9 in the laboratory 3 are the same as the digital camera 1, the reading means 7 and the output means 9 in the first embodiment. Detailed description is omitted. In the second embodiment, the frequency processing is performed on the image data S0 based on the absolute luminance information K in the laboratory 3, and the frequency processing is performed with reference to the database 12 based on the absolute luminance information K. And a frequency processing unit 13 that performs frequency processing on the image data S0 based on the enhancement calculated by the enhancement calculation to obtain processed image data S1. Is provided.

FIG. 6 is a graph showing the relationship between the spatial frequency for each luminance and the eye sensitivity, that is, the frequency response characteristic of the eye.
In addition, the lower side of the plurality of curves shown in FIG. 6 is for low luminance, and the upper side is for high luminance. As shown in FIG. 6, in the scene at the time of shooting, the sensitivity to low frequency components becomes relatively higher as the luminance is lower, and 10
The sensitivity to intermediate frequency components around cycle / mm becomes relatively high. However, in the AE means 5 provided in the digital camera 1, exposure correction is performed so that an image of uniform brightness can be obtained for the original image data S 'regardless of the luminance of the scene at the time of shooting. It is. For this reason, even if a scene with a glaring impression like a sandy beach in midsummer (the frequency response characteristic of the eye corresponds to, for example, curve 1 in FIG. 6) is taken, the image data S0 subjected to the exposure correction is printed. When the output is observed indoors (the frequency response characteristic of the eyes corresponds to curve 2 in FIG. 6),
The low-frequency components appear to be emphasized as compared with other frequency components, and the impression at the time of photographing is impaired. In the second embodiment, based on the absolute luminance information K at the time of shooting, the image data S
0 is subjected to frequency processing. Hereinafter, a specific method thereof will be described.

The database 12 stores data representing the frequency response characteristics of the eyes for each luminance shown in FIG. The emphasis degree calculating means 11 includes the absolute luminance information K read from the recording medium 2, the image data S0, and the database 12
Based on the above data, the degree of emphasis at the time of frequency processing is calculated. Specifically, this is performed as follows. First, the frequency response characteristic of the eyes based on the luminance represented by the absolute luminance information K, that is, the luminance at the time of shooting is curve 1 in FIG. When the frequency response characteristic is curve 2 in FIG. 6, as shown in FIG. 7A, it is assumed that each of curves 1 and 2 has a value over the entire frequency band, and curve 2 is moved upward. To adjust the position of the zero point (FIG. 7B). Then, in order to complement the difference between the frequency response characteristics of the curve 1 and the curve 2 (shaded portion), the frequency response characteristic of the curve 1 in the frequency band is changed to the curve 2 for each limited frequency band of the image data S0. Is obtained as the degree of emphasis.

The frequency processing means 13 performs a frequency emphasis process on the image data S0 based on the emphasis degree calculated by the emphasis degree calculation means 11 to obtain processed image data S1. As the frequency emphasis processing, for example, a frequency processing method described in JP-A-10-75395 can be used. This method uses the image data S0
First, a plurality of blurred image signals having different sharpness levels, that is, different frequency characteristics, are generated based on the above, and a difference between the blurred image signal and two signals in the image data S0 is obtained. A plurality of band-limited image signals (hereinafter referred to as band-pass signals) representing frequency components of the obtained frequency band, and further converting the band-pass signals by the emphasis degree calculated by the emphasis degree calculation means 11, An addition signal is created by integrating the plurality of band-pass signals, and the addition signal is added to the image data S0 to obtain processed image data S1. This processing can be represented, for example, by the following equation (1).

S1 = S0 + β (S0) × Fusm (S0, Sus1, Sus2,... SusN) Fusm (S0, Sus1, Sus2,... SusN) = f ₁ (S0−Sus1) + f ₂ (Sus1-Sus2) +. _k (Susk-1−Susk) +... + f _N (SusN−1−SusN) (1) (however, Susk (k = 1 to N): blurred image signal f _k (k = 1 to N): each band Emphasis degree β (S0) for converting pass signal: emphasis coefficient determined based on image data S0 As described above, frequency processing is performed based on the emphasis degree calculated by emphasis degree calculation means 11, so that a photographing time can be obtained. Is high brightness as shown by curve 1,
Since the intermediate frequency component around 0 cycle / mm is emphasized in comparison with other frequency components, an image obtained by reproducing the processed image data S1 has an impression of a high-luminance scene at the time of shooting. To represent.

Next, the operation of the second embodiment will be described. FIG. 8 is a flowchart showing the operation of the second embodiment. Since the processing from step S11 to step S15 in FIG. 8 is the same as the processing from step S1 to step S5 in the first embodiment, detailed description is omitted here, and step S16 is omitted.
Only the subsequent processing will be described. Emphasis degree calculating means 11
, The absolute luminance information K read by the reading means 7
Based on the image data S0 and the data stored in the database 12, the degree of emphasis when performing frequency processing is calculated (step S16), and the frequency processing unit 13
Is input to The frequency processing means 13 performs the frequency processing represented by the above equation (1) based on the emphasis degree calculated by the emphasis degree calculation means 11, and obtains processed image data S1 (step S17). The processed image data S1 is printed out by the output means 9 (step S18), and the processing is terminated.

As described above, in the second embodiment,
Since the frequency processing is performed on the image data based on the absolute luminance information K relating to the absolute luminance of the scene at the time of shooting, the frequency component corresponding to the luminance at the time of shooting is emphasized, The processed image data S1 representing the image reflecting the luminance can be obtained.
Therefore, by reproducing the processed image data S1, it is possible to obtain an image according to the luminance impression at the time of shooting.

The processed image data S1 reflecting the luminance at the time of photographing is obtained by performing the gradation processing in the first embodiment and the frequency processing in the second embodiment. The processed image data S1 may be obtained by performing both the gradation processing and the frequency processing.

Further, in each of the above embodiments, the digital camera 1 is provided with the luminance meter 6 to measure the luminance at the time of photographing.
This is referred to as the absolute luminance information K. However, based on the original image data S ′ before the exposure correction acquired by the imaging unit 4, the characteristics of the CCD used in the imaging unit 4, the aperture value, and the like are considered. The luminance at the time of shooting may be obtained, and this may be used as the absolute luminance information K. In the case of the digital camera 1 without the AE means 5, the original image data S 'obtained by the imaging means 4 is recorded on the recording medium 2 and transferred to the laboratory 3, but in this case, the characteristics of the CCD Alternatively, information about the aperture value and the aperture value may be recorded on the recording medium 2, and the luminance at the time of photographing may be obtained in the laboratory 3 based on the information and the original image data S ′. Specifically, it can be obtained as follows. Assuming that the exposure amount in the CCD is E, the aperture value (F number) is F, and the absolute luminance of the scene is I, these relations are expressed by the following equation (2).
Can be represented by Note that, in equation (2), k is a constant.

E = k · I / F ² (2) The relationship between the exposure amount of the CCD and the output value from the CCD, that is, the pixel value is determined by the characteristics of the CCD. It can be represented by the following equation (3).

Q = f (E) (3) Therefore, from equations (2) and (3), the absolute luminance I is
The aperture value F and the output value Q from the CCD can be expressed as the following equation (4), and the absolute luminance I obtained in this way may be used as the absolute luminance information K.

I = F ² · f ⁻¹ (Q) / k (4) In each of the above embodiments, the digital camera 1
Is performed on the image data S0 obtained by the above-described method, but the image data obtained by reading the image recorded on the film is also processed based on the absolute luminance information K in the same manner as described above. Keying and / or frequency processing can be performed. In this case, the image data is
The exposure correction may be performed, or the exposure correction may not be performed. Further, in this case, the absolute luminance information K may be recorded on a recording medium such as an FD and transferred to the laboratory 3. When the film is a so-called APS film capable of recording magnetic information, the absolute luminance information K may be recorded in a magnetic recording section of the APS film. Further, information such as an aperture value at the time of photographing may be transferred to the laboratory 3, and the luminance at the time of photographing may be obtained based on the image data obtained at the laboratory 3 and the information, and may be used as the absolute luminance information K.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a configuration of an image output system to which an image processing device according to a first embodiment of the present invention has been applied.

FIG. 2 is a graph showing a relationship between luminance and apparent luminance with respect to luminance.

FIG. 3 is a graph showing only a portion representing luminance contrast in FIG. 2;

FIG. 4 is a flowchart showing the operation of the first embodiment;

FIG. 5 is a schematic block diagram illustrating a configuration of an image output system to which an image processing device according to a second embodiment of the present invention is applied.

FIG. 6 is a graph showing a relationship between a spatial frequency for each luminance and a frequency response characteristic of an eye.

FIG. 7 is a diagram for explaining calculation of a degree of emphasis;

FIG. 8 is a flowchart showing the operation of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Digital camera 2 Recording medium 3 Lab 4 Imaging means 5 AE means 6 Luminance meter 7 Reading means 8 Gradation processing means 9 Output means 11 Emphasis degree calculation means 12 Database 13 Frequency processing means

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Claims (6)

[Claims] 1. An image processing method for performing image processing on image data representing an image acquired by photographing, comprising: acquiring absolute luminance information regarding an absolute luminance of a scene at the time of photographing; An image processing method, comprising: performing image processing for changing gradation and / or frequency characteristics on the image data to obtain processed image data. 2. The image processing according to claim 1, wherein the image represented by the processed image data has a gradation and / or frequency that is close to a gradation and / or frequency characteristic perceived during photographing. 2. The image processing method according to claim 1, wherein the process is a process of changing characteristics. 3. An image processing apparatus for performing image processing on image data representing an image acquired by photographing, comprising: luminance information acquiring means for acquiring absolute luminance information relating to absolute luminance of a scene at the time of photographing; An image processing apparatus comprising: a processing unit configured to perform image processing for changing gradation and / or frequency characteristics on the image data based on information to obtain processed image data. 4. The image processing apparatus according to claim 1, wherein the processing unit is configured to adjust a gradation and / or a frequency of the image data so that an image represented by the processed image data approaches a gradation and / or a frequency characteristic perceived during photographing. 4. The image processing apparatus according to claim 3, wherein said means is a means for performing a process of changing characteristics. 5. A computer-readable recording medium in which a program for causing a computer to execute an image processing method for performing image processing on image data representing an image obtained by photographing is provided. Acquiring the absolute luminance information relating to the absolute luminance of the scene in the above, and performing image processing for changing gradation and / or frequency characteristics on the image data based on the absolute luminance information to obtain processed image data And a computer-readable recording medium. 6. The step of obtaining the processed image data by performing the image processing, wherein the image represented by the processed image data approaches a tone and / or frequency characteristic perceived at the time of shooting. 6. The computer-readable recording medium according to claim 5, wherein the step of performing a process of changing a gradation and / or a frequency characteristic of the image data.