JP4756831B2 - Image photographing apparatus and image processing method - Google Patents

Description

The present invention relates to an image processing technique for performing color matching of images.

  FIG. 1 is a conceptual diagram showing color matching between different devices in general.

  The input data that is RGB data is converted into XYZ data in a color space that does not depend on the device by the input profile. Since colors outside the color reproduction range of the output device cannot be expressed by the output device, color space compression is performed so that all the colors are within the color reproduction range of the output device. After color space compression, the input data is converted from a device-independent color space to CMYK data in a color space that depends on the output device.

  However, in the system shown in FIG. 1, it is difficult to perform color matching under different observation conditions. In order to match the color appearance under different viewing conditions, it is necessary to introduce a human color perception model.

  The human color perception model is designed so that the appearance of human color can be correctly predicted when a color chart having a viewing angle of 2 ° is given, and the human visual field is defined as shown in FIG. In general, CIE1931 colorimetric standard observers can apply in the range of viewing angles from 1 ° to 4 °, so this applicable region is distinguished as a stimulus region within a viewing angle of 2 ° and an adjacent region within a viewing angle of 4 °. . A region from the adjacent region to a viewing angle of 10 ° is defined as a background region, and a region around the background region is defined as a peripheral region. Furthermore, the visual field area including all of the stimulation area, the adjacent area, the background area, and the surrounding area is set as the adaptation area.

Typical color perception models include CIE CAM97s and CIE CAM02. In these models, the observations necessary to convert the relative XYZ values of the color chart into JCh values and QMh values in the color perception space independent of the observation conditions. The condition parameters are defined as follows.
LA: Absolute luminance of adaptation area (hereinafter referred to as adaptation luminance) [cd / m ² ]
Xw, Yw, Zw: White point relative X, Y, Z value
Yb: Relative luminance of the background area (hereinafter referred to as background luminance [%])
Surround: Ambient light level
-Average Surround
-Dim Surround
-Dark Surround
Here, the adaptation brightness is usually set to 20% of the absolute brightness of the white point in the adaptation area, and the ambient light level is Average if the relative brightness in the surrounding area is 20% or more of the white point in the adaptation area, and less than 20%. If it is almost 0%, Dark is set.

  Since the color perception model was derived from experimental results using a single color chart, it has been established what observation condition parameters should be applied to images with multiple colors. Was not. That is, since neutral gray is 20% of the white point, Yb is generally set to 20%.

  When applying a color perception model to an image, it is common to use one observation condition parameter for all pixels.

  FIG. 3 is a conceptual diagram extended so that input / output observation conditions (white point, adaptation luminance, background luminance, ambient light level) can be considered in color matching between different devices.

  Input data which is RGB data under the D50 light source is converted into XYZ data under the D50 light source by the input profile. XYZ data under a D50 light source is converted into JCh data or QMh data in a color space independent of the viewing conditions by giving the viewing conditions on the input side to the color perceptual model forward conversion. JCh data or QMh data is converted to XYZ data under the A light source by giving the output side observation condition to the inverse color perception model. Further, the XYZ data under the A light source is converted into CMYK data under the A light source by the output profile. Here, the color space compression may be performed in a color space that does not depend on viewing conditions, or may be performed in an XYZ space under the A light source.

  Conventionally, input / output observation condition parameters (white point, adaptation luminance, background luminance, ambient light level) have been set by using a user interface or observation condition parameters stored in advance in a profile. However, setting by the user interface is complicated and difficult for a general user to understand, and the method for selecting a profile has to prepare as many profiles as the number of observation conditions. In order to prevent an increase in the number of profiles, the observation condition parameter in the profile can be updated by the user interface, but the troublesomeness for the user has not been solved.

In particular, in setting the observation conditions for the digital camera image, it is difficult to set appropriate observation condition parameters because the observation conditions at the shooting site are unknown and the shooting conditions are different.
JP2000-050086A JP 2000-050088 A JP 2000-050089 A

Thus, in the conventional setting method of observation condition parameters,
(1) Special knowledge was required for setting observation conditions.
(2) In order to store a plurality of observation conditions, as many profiles as the number of observation conditions are required.
(3) The observation conditions at the shooting site are unknown.
There was a problem.

An object of the present invention is to automatically set adaptive luminance information and background luminance information according to the situation at the time of image shooting , and to reduce the burden on the user for setting color matching observation conditions.

In order to solve the above-described problems and achieve the object, the image capturing apparatus of the present invention sets an exposure condition from luminance information in a plurality of photometric areas and performs focus detection of the areas corresponding to the photometric areas. An imaging apparatus for determining a focal point, wherein adaptive luminance information indicating luminance of an adaptive region in a human color perception model is obtained from the luminance information in the photometric area used for determining the focal point, and the focal point is determined. Means for obtaining background luminance information indicating the luminance of the background region in the human color perception model from the luminance information in the photometric area not used for the image, and using the adaptive luminance information and the background luminance information as image additional information Storage means for storing in a file.

According to the present invention, it is possible to automatically set appropriate adaptation luminance information and background luminance information according to the situation at the time of image capturing, and it is possible to reduce the burden on the user for setting the observation condition for color matching .

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings.

  The embodiment described below is an example as means for realizing the present invention, and the dimensions, shapes, relative arrangements, and the like of the constituent elements exemplified below are the configurations of the apparatus to which the present invention is applied. It should be modified or changed as appropriate according to various conditions, and the present invention is not limited to the following embodiments.

Further, the present invention supplies a storage medium (or recording medium) storing software program codes for realizing the functions of the embodiments described later to the system or apparatus, and the computer of the system or apparatus (or CPU or MPU). Needless to say, this can also be achieved by reading and executing the program code stored in the storage medium.
[Calculation of observation conditions for digital cameras]
FIG. 4 shows a divided photometric sensor corresponding to a distance measuring point in the digital camera. Here, it is assumed that the distance measuring point corresponding photometric sensor has focus detection points S0 to S20 corresponding to the divided photometric areas S0 to S20.

  The principle of focus detection is that each image is formed on a CCD formed as a pair of line sensors by light beams that pass through different areas of the photographic lens, and the relative position difference between these imaged images ( Hereinafter, the image signal representing the spatial phase difference between the two images is utilized by utilizing that the defocus amount is proportional to the amount of deviation between the in-focus point and the detected focus state of the photographing lens. Appropriate calculation is performed to calculate the focal state at that time, that is, the shift direction from the in-focus state and the moving distance of the photographic lens required to the in-focus point.

  FIG. 5 shows an observation condition calculation flow.

  First, photometry is performed on the subject, and the exposure conditions (aperture and shutter speed) are calculated from the luminance information obtained from the photometric areas S0 to S20 (T1).

  Next, focus detection is performed on the subject at the focus detection points S0 to S20 (T2), and the focal point is determined from the detection result (T3). If the focal point is determined, the lens drive amount is calculated based on the result, and the lens is driven (T4, T5).

Next, in steps T6 and T7, an area used for focusing (small defocus amount) is classified into an area not used for focusing (large defocus amount), and an area with a large defocus amount is used. Consider background. For example, the areas used for focusing are S0, S5, S6, S7, S8, S9, S12, and the areas not used for focusing are S1, S2, S3, S4, S10, S11, S13, S14, S15. , S16, S17, S18, S19, and S20, the average brightness Yaf [cd / m ² ] of the metering area corresponding to the area used for focusing, and the metering area corresponding to the area not used for focusing The average luminance Ynaf [cd / m ² ] can be calculated as follows in consideration of weighting according to the area and position of each area.
Yaf = Cs0 / Ys0 + Cs5 / Ys5 + Cs6 / Ys6 + Cs7 / Ys7 + Cs8 / Ys8 + Cs9 / Ys9 + Cs12 / Ys12 [cd / m ² ]
Ynaf = Cs1 · Ys1 + Cs2 · Ys2 + Cs3 · Ys3 + Cs4 · Ys4 + Cs10 · Ys10 + Cs11 · Ys11 + Cs13 · Ys13 + Cs14 · Ys14 + Cs15 · Ys15 + Cs16 · Ys16 + Cs17 · Ys17 + Cs18 · Ys18 + Cs19 · Ys19 + Cs20 · Ys20 [cd / m 2]
Here, Ysi is luminance information output from the photometric area i, and Csi considers weighting according to the area and position of the photometric area i and converts the unit of the luminance information to [cd / m ² ]. It is a coefficient to do.

In the case of a digital camera, the adaptation brightness from the photometric information for the subject is
LA = Yaf [cd / m ² ]
Can be actually measured.

However, since the absolute luminance of the white point cannot be measured at the same time, the background luminance Yb [%] is determined by the following method.
(1) When manual exposure is set (T9)
When using the manual exposure setting, the luminance for 18% gray is estimated from the exposure conditions (aperture, shutter speed) and film sensitivity set under the same observation conditions as the subject, and the background luminance Yb is obtained. Between the exposure conditions (aperture Av, shutter speed Tv) determined from the Ev value of the exposure meter and the film ISO sensitivity Sv and brightness Bv, APEX (Additive Photographic Exposure) value is Ev = Av + Tv = Bv + Sv Because the relationship is established,
Bv = Av + Tv-Sv
= 2log ₂ (F) -log ₂ (T) -log ₂ (ISO / 3.125)
For example, if the aperture is F2.8, the shutter speed is 1/160 seconds, and ISO 200,
Bv = 2log ₂ (2.8) -log ₂ (1/160) -log ₂ (200 / 3.125) = 4.32 [APEX]
Furthermore, the relationship with luminance B [cd / m ² ] for 18% gray is
Bv = log ₂ (B / NK), NK = 3.426
Because
B = 3.426 ・ (2 ^Bv ) = 65.11 [cd / m ² ]
Incidentally, the absolute brightness of the white point is B / 0.18 = 65.11 / 0.18 = 361.73 [cd / m ² ].

From this, the background brightness is
Yb = 18 ・ Ynaf / B [%]
Can be calculated as Further, when all areas are used for focusing and Ynaf cannot be calculated, Yb = 20 [%] is set.
(2) When AE is set (T10)
When using the AE (automatic exposure) setting, measure a gray chart with a known reflectance under the same observation conditions as the subject using a digital camera, and register the calculated average brightness as a reference value in advance. It is necessary to keep.

For example, if the average luminance Yg [cd / m ² ] for the gray chart (18% gray) is previously manually registered in the memory of the digital camera body, the background luminance is
Yb = 18 ・ Ynaf / Yg [%]
Can be calculated as

  Further, when all areas are used for focusing and Ynaf cannot be calculated, Yb = 20 [%] is set.

  In the case of a digital camera, the ambient light level Surround is considered to be an extension of the background, and is set so as to be linked to Yb (T11). That is, if Yb is 20% or more, it is Average, if it is smaller than 20%, it is Dim, and if it is almost 0%, it is Dark.

  The relative X, Y, and Z values Xw, Yw, and Zw of the white point are converted from the color temperature set in the white balance information (Auto / preset / manual / color temperature) of the digital camera (T12).

  By the above method, the observation condition parameters for the shooting conditions at the shooting site are determined from the internal information of the digital camera and stored in the image file as additional information of the image (T13).

  Even if only the observation conditions are stored as manufacturer-dependent data information for Exif tags, the observation condition parameters are stored in the image file as private tags for device profiles such as ICC profiles and stored as embedded profiles in images. It doesn't matter.

  The observation condition parameters stored in the image file are extracted from the image file and used as input-side observation conditions when performing color matching considering the observation conditions as shown in FIG.

According to the said embodiment, there exist the following effects.
(1) By storing the observation condition parameters in the image file as image additional information, the setting of the input side observation conditions can be automated.
(2) By storing observation condition parameters as additional information of a profile and embedding the profile in an image file, setting of input observation conditions and profile selection can be automated.
(3) By calculating the observation conditions from the imaging conditions, it is possible to calculate the observation condition parameters corresponding to the imaging site.
(4) By using the output and distance measuring point information sent from the divided distance measuring point corresponding photometric sensors, it is possible to calculate an accurate observation condition parameter according to the photographing site.

It is a figure which shows the prior art example of the color matching between different devices. It is a figure explaining the definition of a human visual field. It is the conceptual diagram expanded so that the input / output observation conditions could be considered in the color matching between different devices. It is a figure which shows the photometry sensor corresponding to the ranging point divided | segmented in the digital camera. It is a flowchart for observation condition calculation.

Claims (4)

An image capturing device that sets an exposure condition from luminance information in a plurality of photometric areas, detects a focal point of an area corresponding to each photometric area, and determines a focal point,
The luminance information in the photometric area not used for determining the focal point is obtained by obtaining adaptive luminance information indicating the luminance of the adaptive region in the human color perception model from the luminance information in the photometric area used for determining the focal point. Means for obtaining background luminance information indicating the luminance of the background region in the human color perception model from the information;
An image photographing apparatus comprising: storage means for storing the adaptive luminance information and the background luminance information as image additional information in an image file.   The luminance information in the photometric area used for determining the focal point and the luminance information in the photometric area not used for determining the focal point are the luminance information obtained from each photometric area. The image capturing apparatus according to claim 1, wherein the image capturing apparatus is obtained by multiplying a weighting coefficient corresponding to an area and a position.   The image photographing apparatus according to claim 1, wherein the adaptation luminance information and the background luminance information are used as an observation condition on the input side when color matching is performed on the image. An image processing method in an image capturing apparatus that sets an exposure condition from luminance information in a plurality of photometric areas, performs focus detection of an area corresponding to each photometric area and determines a focal point,
The luminance information in the photometric area not used for determining the focal point is obtained by obtaining adaptive luminance information indicating the luminance of the adaptive region in the human color perception model from the luminance information in the photometric area used for determining the focal point. Obtaining background luminance information indicating the luminance of the background region in the human color perception model from the information;
An image processing method comprising: storing the adaptive luminance information and the background luminance information in an image file as additional information of an image.

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