JP2011120299A - Gradation conversion apparatus, program, electronic camera, and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gradation conversion apparatus and method by which partial contrast is appropriately adjusted, with contrast balance of a whole image being adjusted by using an arbitrary gradation conversion property. <P>SOLUTION: This gradation conversion apparatus used for converting the gradation of an original image is equipped with: a signal obtaining unit 12; a neighborhood processing unit 13, a gain generator 14; and a gradation conversion unit 15. The signal obtaining unit 12 extracts or generates a signal Z[i, j] from a pixel [i, j] of the original image. The neighborhood processing unit 13 generates a signal ZL[i, j] related to a neighborhood area of the pixel [i, j]. The gain generation unit 14 determines a conversion gain k of the pixel [i, j] corresponding to the signal Z[i, j] and the signal ZL[i, j]. The gradation conversion unit 15 performs gradation conversion by multiplying either the color component of the pixel [i, j] or the signal component generated from the color component by the conversion gain k of the pixel [i, j]. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gradation conversion device, a program, an electronic camera, and a method thereof using an image gradation conversion technique.

(Prior Art 1)
Conventionally, a gradation conversion technique described in Patent Document 1 below is known.
In this prior art, first, the luminance signal Y is obtained by the following equation.
Y = 0.3 ・ R + 0.59 ・ G + 0,11 ・ B ... [1]
Next, a predetermined gradation conversion Y ′ = f (Y) is performed on the luminance signal Y to obtain a converted luminance signal Y ′. In this gradation conversion, a gamma conversion characteristic f (Y) = Y ^ γ or a free nonlinear function is used. The ratio before and after the conversion is calculated and set as the conversion gain k (Y).
By multiplying this conversion gain k (Y) by each of the color components RGB of the image,
R ′ = k (Y) · R
G ′ = k (Y) · G
B ′ = k (Y) · B [2]
And the color component R′G′B ′ after gradation conversion is obtained.

(Retinex method)
Conventionally, the Retinex Method is also known as a gradation correction method. In the Retinex method, it is possible to emphasize a minute change in gradation and raise a gradation hidden in a dark portion or the like.

JP-A-4-150171

  By the way, since the conventional technology of Patent Document 1 uses a single gradation conversion characteristic, it is suitable for adjusting the overall light / dark balance of the entire screen. However, it is impossible to perform image processing that particularly emphasizes the gradation of details to enhance the sharpness and detail of the image.

  On the other hand, the conventional technique of the Retinex method cannot freely control the light / dark balance of the entire image. For this reason, it has been difficult to perform a process of enhancing the gradation of details at the same time while adjusting the overall brightness balance of the image.

  The object of the present invention is to further improve the appearance of detailed gradation while adjusting the overall light / dark balance of the entire image using arbitrary gradation conversion characteristics, which is impossible with the above two conventional techniques. It is to provide a gradation conversion technique that can be adjusted.

<< 1 >> The gradation conversion apparatus of the present invention is an apparatus that converts the gradation of an original image, and includes a signal acquisition unit, a neighborhood processing unit, a gain generation unit, and a gradation conversion unit.
The signal acquisition unit extracts or generates a signal Z [i, j] that changes according to at least the brightness of the pixel [i, j] of the original image.
The neighborhood processing unit generates a signal ZL [i, j] that changes according to at least the brightness of the neighborhood region of the pixel [i, j].
The gain generation unit determines the conversion gain k of the pixel [i, j] corresponding to the signal Z [i, j] and the signal ZL [i, j].
The gradation conversion unit performs gradation conversion by multiplying the conversion gain k of the pixel [i, j] by the color component of the pixel [i, j] or a signal component generated from the color component.

<< 2 >> Preferably, the gain generation unit generates a combined signal Z1 (Z, ZL) of the signal Z [i, j] and the signal ZL [i, j]. The gain generation unit substitutes the combined signal Z1 (Z, ZL) for a predetermined gain curve function k = k (Z1) to obtain the conversion gain k of the pixel [i, j].

<< 3 >> Preferably, the gain generation unit decreases the conversion gain k when the signal Z [i, j] increases and decreases the signal ZL [i, j].

<< 4 >> Preferably, the signal Z [i, j] is a signal relating to the luminance or brightness of the pixel [i, j].

<< 5 >> Also preferably, the signal Z [i, j] is a signal reflecting the brightness and saturation of the pixel [i, j], and has a larger value as the saturation is higher even if the brightness is the same. It is a signal which shows.

<< 6 >> Preferably, the signal ZL [i, j] is a signal obtained based on the brightness of the pixel [i, j] and the neighboring pixels of the pixel [i, j].

<< 7 >> Preferably, the gain generation unit obtains the conversion gain k by the following processes (1) to (3).
(1) Obtain signals X and XL by calculation to obtain the reciprocals of signals Z and ZL,
(2) The signals X and XL are combined to generate a combined signal X1,
(3) Processing for performing at least one of “gain limiter”, “power”, “gain reduction near 0”, and “gain closer to 1 when Z becomes greater than a predetermined value” with respect to the synthesized signal X1 h () to obtain conversion gain k = h (X1) << 8 >> Preferably, the gradation conversion unit obtains a color signal C representing an amount related to color difference or saturation from the original image, The signal C is multiplied by the conversion gain k1 to generate a tone-converted color signal. However, the conversion gain k1 is k1 = k · t (Z) or k1 (Z, ZL) = k (t (Z), ZL) where t (Z) is a function that monotonously changes with respect to Z.

<< 9 >> The gradation conversion program of the present invention functions as a signal acquisition unit, a neighborhood processing unit, a gain generation unit, and a gradation conversion unit according to any one of the above << 1 >> to << 8 >>. It is a program to make it.

<< 10 >> An electronic camera according to the present invention includes the gradation conversion device according to any one of the above << 1 >> to << 8 >>, and an imaging unit that images a subject to generate an original image. And this electronic camera performs gradation conversion of the original image produced | generated by the imaging part using the gradation converter.

<< 11 >> The gradation conversion method of the present invention is a method for converting the gradation of an original image, and includes the following steps.
(1) A step of extracting or generating a signal Z [i, j] that changes according to at least the brightness of the pixel [i, j] of the original image.
(2) A step of generating a signal ZL [i, j] that changes in accordance with at least the brightness of the vicinity region of the pixel [i, j].
(3) A step of determining a conversion gain k of the pixel [i, j] corresponding to the signal Z [i, j] and the signal ZL [i, j].
(4) A step of performing gradation conversion by multiplying the conversion gain k of the pixel [i, j] by the color component of the pixel [i, j] or a signal component generated from the color component.

  In the present invention, the conversion gain k of the pixel [i, j] is increased or decreased depending on not only the signal Z obtained from the pixel [i, j] of the original image but also the signal ZL obtained from the neighborhood region thereof. . As a result, the value of the conversion gain k is different between the dark neighboring area and the bright neighboring area, and gradation conversion that adjusts the appearance of detailed gradation is possible.

It is a block diagram which shows the structure of a gradation converter. It is a block diagram which shows the structure of an electronic camera. It is a figure which shows an example of a gradation conversion characteristic. It is a flowchart which shows the image processing operation in embodiment. It is a figure which shows an example of a gradation conversion characteristic.

<Description of configuration>
FIG. 1 is a diagram illustrating a configuration of the gradation conversion device 11.
In FIG. 1, the gradation conversion device 11 has the following configuration requirements.
(1) Signal acquisition unit 12... Obtains a signal Z indicating the brightness of each pixel of the original image.
(2) Proximity processing unit 13... Processes pixels in the vicinity of each pixel of the original image to obtain a signal ZL.
(3) Gain generating unit 14... For each pixel, a conversion gain k is obtained from the signal Z and the signal Z.
(4) Tone conversion unit 15... Tone conversion is performed by multiplying the signal of each pixel of the original image by the conversion gain k of each pixel.

  The above-described gradation conversion device 11 may be partially or entirely configured by hardware. Further, the gradation conversion apparatus 11 may be realized as software on a computer by using a gradation conversion program.

FIG. 2 is a diagram showing an electronic camera 21 equipped with such a gradation conversion device 11.
In FIG. 2, a photographing lens 22 is attached to the electronic camera 21. On the image space side of the photographic lens 22, an imaging surface of the imaging element 23 is arranged via a diaphragm and a shutter (not shown). The image signal output from the image sensor 23 is input to the gradation conversion device 11 as an original image after passing through the A / D converter 24 and the like. The gradation conversion device 11 performs gradation conversion on the original image. The image signal output from the gradation conversion device 11 is subjected to image processing via the image processing unit 25 and then stored and recorded in the recording unit 26.
Note that the gradation conversion device 11 can read out the recorded image data from the recording unit 26 later and perform gradation conversion.

<< Description of Principle of Embodiment >>
First, the principle of the feature of this embodiment will be described.
In this embodiment, a reference gradation conversion characteristic (curve) is set in advance. For example, when correcting an image shot in a backlight state, gradation conversion as shown in FIG. 3A is performed so that the dark part is lifted brighter. Assuming that the signals before and after the gradation conversion are Z and Z ′, this gradation conversion is expressed by an equation:
Z ′ = Z ^ q [9]
(Eg q = 0.6)
It becomes.
In this case, the conversion gain k is
k (Z) = Z ′ / Z = 1 / (Z ^ p) (10)
(However, p = 1-q)
It becomes. FIG. 3B is a diagram illustrating the relationship between the signal Z and the conversion gain k.
In this way, it changes depending on the conversion gain k of the non-linear gradation conversion characteristic and the value of the signal Z before conversion.

Next, in the present embodiment, a signal related to the brightness of a pixel in the vicinity region of the pixel [i, j] is obtained and set as ZL. For example, the signal ZL may be an average of values indicating the brightness of neighboring pixels, or a predetermined spatial frequency component (for example, a predetermined subband component or a predetermined low frequency component) is extracted for the image brightness. The value of the pixel [i, j] of the extracted image may be adopted as the signal ZL.
From such a magnitude relationship between the signals Z and ZL, it is known how to set the gradation of the detailed image, that is, “how the signal Z of the pixel [i, j] has changed from the nearby signal ZL”. be able to.

Therefore, in this embodiment, the conversion gain k is adjusted to increase or decrease depending on the magnitude relationship between the signals Z and ZL. As a result, it is possible to adaptively emphasize the way in which the gradation of details is raised or to suppress adaptively.
Such an adaptive increase / decrease adjustment of the conversion gain k is performed, for example, by converting the conversion gain k (Z) that is dependent only on the signal Z to the conversion gain k (() that depends on the composite signal Z1 = (Z + ZL) / 2 or the like. This is realized by replacing with Z1).
Here, the adaptive increase / decrease adjustment of the conversion gain k will be described separately for the monotonically decreasing region and the monotonically increasing region of k (). First, in the monotonically decreasing region of k (), the conversion gain k (Z1) shows the following increase / decrease change with respect to the original conversion gain k (Z).

(1) When Z = ZL, since Z1 = Z, k (Z1) = k (Z).
(2) In the case of Z <ZL, since Z1> Z, k (Z1) <k (Z).
(3) When Z> ZL, since Z1 <Z, k (Z1)> k (Z).

  The above (1) is a place where there is little change in gradation of details. In such a place, k (Z1) is equal to the original k (Z). Therefore, the global tone conversion characteristics that affect the entire image are substantially equal to the preset tone conversion characteristics. Therefore, it is possible to avoid the adverse effects such as the dark part of the image being bright and floating too much.

  On the other hand, the above (2) and (3) are places where gradation changes occur in detail. About these places, the increase / decrease change of k (Z1) arises in the direction which expands the contrast of a near region (signal ZL) and the signal Z. For this reason, in the monotonically decreasing region of k (), how to stand out in detail is adaptively emphasized.

  On the other hand, in the monotonically increasing region of k (), since the increase / decrease change opposite to the above occurs in k (Z1), it is possible to adaptively suppress the appearance of detailed gradation.

  Note that by setting k () using an LUT (look-up table) or the like, it is easy to appropriately allocate the input range of Z1 to the monotonically decreasing region and the monotonically increasing region. For example, as shown in FIG. 3C, an intermediate range excluding the vicinity of 0 and the vicinity of the upper limit of Z1 can be a monotonically decreasing range of k (). With such a design, it is possible to adaptively emphasize the manner in which the gradation of details appears in the visually effective intermediate region.

  Further, in the above description, the conversion gain k increase / decrease adjustment is realized by changing the argument of the conversion gain k () from Z to Z1. However, the conversion gain k may be adaptively increased or decreased by changing the argument of the conversion gain k () from Z to (Z, ZL). In this case, it is preferable to decrease the gain k when the signal Z increases and decrease the gain k when the signal ZL increases. Such processing makes it possible to enhance the gradation of dark image regions while suppressing signal saturation after gradation conversion.

  As the signal Z, a “signal related to luminance or lightness” or a “signal that reflects the brightness and saturation and shows a larger value as the saturation is the same even with the same brightness” may be used. In particular, when a signal Z that reflects brightness and saturation is used, it is possible to moderately suppress color saturation after gradation conversion.

  Alternatively, the signals X and XL corresponding to the reciprocals of the signals Z and ZL may be obtained, and the signals X and XL may be combined to generate the combined signal X1. In the above equation [10], the gradation conversion gain k is obtained by performing non-linear processing such as exponentiation on the reciprocal value of the signal Z. Therefore, processing h (such as “gain limiter”, “power”, “gain reduction near 0”, or “gain closer to 1 when Z becomes greater than a predetermined value” with respect to the composite signal X1 corresponding to the reciprocal. ) Can be appropriately designed to design a desired gain curve. In this case, since the composite signal X1 changes in accordance with the magnitude relationship between the signals Z and ZL, the conversion gain k = h (X1) obtained by processing the composite signal X1 naturally increases and decreases. As a result, by multiplying the image by this conversion gain k, it becomes possible to adjust the way in which the detailed gradation is raised.

  Instead of the signals Z, ZL, X, and XL, signals obtained by performing non-linear processing such as exponentiation or normalization on the signals Z, ZL, X, and XL may be used. Further, the combined signals Z1 and X1 are not limited to the weighted addition of the original signals. For example, the higher-order term of the original signal may be added to the calculation formula for the combined signals Z1 and X1. By such variation, it becomes possible to set the increase / decrease adjustment of the conversion gain k more finely.

  Further, there are cases in which the saturation changes in an undesired direction with gradation conversion. In this case, by correcting the saturation according to the conversion gain k depending on the signals Z and ZL, it is possible to perform the saturation correction that fully considers the effect of the increase / decrease adjustment of the conversion gain k.

<Specific example of gradation conversion>
Next, specific processing of gradation conversion will be described with reference to FIG.

[Step S1] The gradation conversion apparatus 11 captures an original image. This original image is composed of color components such as (R, G, B), (Y, Cr, Cb), (L, a, b). In some cases, RAW data having missing color components in pixel units is input as an original image.

[Step S2] The signal acquisition unit 12 extracts or generates a signal Z [i, j] for the pixel [i, j] of the original image. [I, j] indicates the coordinates of the pixel.
As the signal Z, a luminance signal Y (Y = a1, R + a2, G + a3, B) calculated from RGB color components may be employed. When the original image is expressed in the YCrCb color space, the luminance signal Y can be used as it is. Further, when the original image is expressed in the Lab color space, the lightness L can be used as it is.
However, when tone conversion is performed based on the luminance signal Y described above, there is an adverse effect that regions with high saturation of red and blue are likely to be saturated after tone conversion. Therefore, it is preferable to employ a signal that reflects not only brightness but also saturation as the signal Z. A signal preferable as such a signal Z, when considered in terms of RGB components, has a large contribution of R when R is large, a large contribution of G when G is large, and a large contribution of B when B is large. It is a function like this. For example, if the original image is a signal in the RGB color space, it is preferable to obtain Z = max (R, G, B).
Also, for example, if the original image is a signal in the YCrCb color space or Lab color space, Z = max (R, G, B) may be obtained after being converted into RGB once. In addition, by performing signal synthesis related to brightness and saturation using the following [11] and [12], the signal Z approximated to max (R, G, B) can be generated at high speed with a small processing load. Can be sought.
Z = Y + w1 · | Cr | + w2 · | Cb | ... [11]
Z = L + w1 · | a | + w2 · | b |
(For example, w1 = w2 = 1/2 is preferable)
The signal Z reflecting both the brightness and the saturation becomes a signal indicating a higher value as the saturation is higher and the saturation is more likely even if the brightness is dark.
Further, for example, in the case where the original image is RAW data having a missing color component for each pixel, the signal Z can be obtained by substituting a neighboring color component instead of the missing color component of the pixel [i, j]. Good. Further, the signal Z may be obtained after the missing color component of the RAW data is generated by the interpolation process.
The signal Z may be subjected to non-linear processing such as exponentiation or preprocessing such as normalization.

[Step S3] The neighborhood processing unit 13 obtains a signal ZL [i, j] related to the neighborhood region of the pixel [i, j]. For example, smoothing, low-passing, or blurring processing is performed on the image signal in the vicinity area (for example, the signal Z, the color signal, or a signal that reflects the synthesized value of the color signal, brightness, and saturation). Perform signal ZL. Note that, as a material for obtaining the signal ZL, it is preferable to use the signal Z as it is when considering a reduction in the processing load.
Specifically, a plurality of image signals located in the vicinity region are used as a population, and an average value, a weighted average value, a median value, a most frequent value, an average value of values excluding a minimum maximum, and a signal Z are predetermined. An average value or the like of neighboring pixel values that fall within the range is obtained as a signal ZL.
Preferably, a pixel whose value is as distant as the pixel [i, j] is selected from neighboring pixels around the pixel [i, j], and an image signal of the pixel or a local average value thereof is obtained. The signal ZL may be used. In this case, since the anisotropic image structure is reflected in the values of the signals Z and ZL, as a result, it is possible to adjust (emphasize or suppress) the way the anisotropic gradation stands.
Further, for example, when the original image is RAW data having a missing color component in pixel units, the signal ZL can be obtained by substituting a neighboring color component instead of the missing color component of the pixel [i, j]. Good. Further, the signal ZL may be obtained after the missing color component of the RAW data is generated by the interpolation process.
It should be noted that an appropriate value in the range of about 0.01 to 0.5 of the diagonal length of the original image, such as 0.05, is preferable as a guideline for the radius r indicating the size of the neighborhood region. Alternatively, the signal ZL may be obtained for each of a plurality of radii, and these may be weighted and averaged to form the signal ZL.
Note that this signal ZL may also be subjected to non-linear processing such as exponentiation or preprocessing such as normalization.

[Step S4]
The gain generation unit 14 determines the conversion gain k of the pixel [i, j] corresponding to the signal Z [i, j] and the signal ZL [i, j]. Hereinafter, each variation of the method of determining the conversion gain k will be described individually.

(Determination method 1)
In the gain generation unit 14, a correspondence relationship between the signals Z and ZL and the conversion gain k is set in advance by an expression or an LUT. In this correspondence, when the signal Z increases, the conversion gain k (Z, ZL) decreases, and when the signal ZL increases, the conversion gain k (Z, ZL) decreases. The gain generator 14 collates the signals Z and ZL with this correspondence to determine the corresponding conversion gain k.

(Determination method 2)
First, the gain generation unit 14 normalizes the signals Z and ZL using predetermined values Z0, ZL0, and γ determined for normalization, and calculates the signals S and SL.
S = Z / Z0, or S = (Z / Z0) ^ γ,
SL = ZL / ZL0 or SL = (ZL / ZL0) ^ γ
Next, the gain generation unit 14 uses the signals S and SL,
Z1 = δ + a1 · S + a2 · SL,
Or Z1 = δ + a1, S + a2, SL + a3, S, SL + a4, S, S + a5, SL, SL + (higher order terms of S, SL)
(Where coefficients a1, a2,... Are predetermined constants, and δ is 0 or a predetermined constant)
To generate a composite signal Z1.
In the gain generation unit 14, a function k () that matches the gain curve is set in advance by an expression or LUT. For example, a function such as k (Z1) = x ^ p (where −0.1> p ≧ −1) is preferable. The gain generation unit 14 obtains the conversion gain k (Z1) by substituting the obtained composite signal Z1 into the function k () indicating this gain curve.

(Determination method 3)
First, the gain generating unit 14 normalizes the signals Z and ZL using predetermined values Z0, ZL0, and γ ′ determined for normalization, and calculates the following reciprocal signals X and XL.
X = Z0 / (Z + δ), or X = (Z0 / (Z + δ)) ^ γ ′,
XL = ZL0 / (ZL + δ), or XL = (ZL0 / (ZL + δ)) ^ γ ′
(Where δ is 0 or a predetermined constant)
Next, the gain generation unit 14 uses the reciprocal signals X and XL,
X1 = δ + a1 · X + a2 · XL,
Or, X1 = δ + a1 · X + a2 · XL + a3 · X · XL + a4 · X · X + a5 · XL · XL + (higher order terms of X and XL)
To generate a composite signal X1.
(Where coefficients a1, a2,... Are predetermined constants, and δ is 0 or a predetermined constant)
Next, the gain generation unit 14 performs a predetermined process h () on the combined signal X1 to obtain a conversion gain k = h (X1).
The processing h () here is “gain limiter”, “power”, “gain reduction near 0”, “gain closer to 1 when Z is greater than a predetermined value” and “curve” with respect to the synthesized signal X1. This is a process of applying at least one of “shape change” and “gain suppression of the high luminance part”.

FIG. 5 is a diagram illustrating an example of such processing h ().
FIG. 5A shows the relationship between the signals Z and ZL and the combined signal X1.
FIG. 5B shows a case where the “gain limit” is applied by limiting the upper limit of the combined signal X1.
FIG. 5C illustrates a case where “a process for bringing the gain closer to 1 when the signal Z exceeds a predetermined value” is performed.
FIG. 5D is a case where the processes of FIGS. 5B and 5C are performed in combination.

[Step S5]
The gradation conversion unit 15 performs gradation conversion by multiplying the conversion gain k obtained for the pixel [i, j] by the color component of the pixel [i, j] or a signal component generated from the color component.

(Case 1) When a plurality of color components constituting the original image are R, G, and B, R ′, G ′, and B ′ signals converted using this conversion gain are R ′ = k · R, G ′ = k · G, B '= k · B
Calculated by

(Case 2) In the case of a brightness signal representing an amount related to luminance or brightness and an input signal related to a plurality of color differences, the brightness signal which has been subjected to gradation conversion is calculated by multiplying the brightness signal by a conversion gain k. Furthermore, when the input signals regarding a plurality of color differences are C1 and C2,
C1 ′ = k · C1, C2 ′ = k · C2
Thus, the color differences C1 'and C2' after gradation conversion are obtained.
Note that saturation may change in appearance due to tone conversion. When correcting such a saturation change, the corrected conversion gain k1 is used instead of the conversion gain k.
C1 ′ = k1 · C1, C2 ′ = k1 · C2
Here, the corrected conversion gain k1 is t (Z), which is a function that changes monotonously with respect to Z.
k1 = k · t (Z) or k1 (Z, ZL) = k (t (Z), ZL). The function t (Z) is preferably determined experimentally so that the apparent saturation is appropriate.

(Case 3) In the case of a brightness signal representing an amount related to brightness or brightness and an input signal related to saturation C, the brightness signal multiplied by the conversion gain k (Z) is calculated to calculate a brightness-converted brightness signal. Further, C1 ′ = k · C is calculated with C ′ representing the tone-converted saturation. In addition, it is good also as C '= k1 * C using said k1.

(Case 4) For a signal in the Lab color space, L′ a′b ′ after gradation conversion is
L ′ = k · L, a ′ = k · a, b ′ = k · b
Calculated by In addition, it is good also as a '= k1 * a and b' = k1 * b using said k1.

<< Additional items of embodiment >>
In the above-described embodiment, the case where gradation conversion is performed using a gradation conversion device, a computer, or an electronic camera has been described. However, the present invention is not limited to this. For example, an image processing server (such as an image album server) on the Internet may provide the above-described gradation conversion method for image data transmitted from a user.

  In the above-described embodiment, the case where gradation conversion is performed on the entire screen has been described. However, the present invention is not limited to this. For example, gradation conversion may be performed only on a part of the screen (main subject, shadow portion, trimming range, face recognition region, background portion excluding a person or skin color region, etc.).

  In the above-described embodiment, the signal ZL and the like are generated from the original image. However, there are cases where an electronic camera generates a reduced image separately. In such a case, it is preferable to acquire or generate the signal ZL from the reduced image. With such an operation, it is possible to further shorten the processing time for gradation conversion.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the above-described embodiments are merely examples in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the present invention is a technique that can be used for image processing and the like.

DESCRIPTION OF SYMBOLS 11 Gradation conversion apparatus 12 Signal acquisition part 13 Neighborhood processing part 14 Gain generation part 15 Gradation conversion part

Claims (11)

A gradation conversion device for converting the gradation of an original image,
A signal acquisition unit that extracts or generates a signal Z [i, j] that changes according to at least the brightness of the pixel [i, j] of the original image;
A neighborhood processing unit that generates a signal ZL [i, j] that changes according to at least the brightness of the neighborhood of the pixel [i, j];
A gain generation unit for determining a conversion gain k of the pixel [i, j] corresponding to the signal Z [i, j] and the signal ZL [i, j];
A gradation conversion unit that performs gradation conversion by multiplying the conversion gain k of the pixel [i, j] by a color component of the pixel [i, j] or a signal component generated from the color component; A gradation converter characterized by that. The gradation converter according to claim 1,
The gain generation unit generates a combined signal Z1 (Z, ZL) of the signal Z [i, j] and the signal ZL [i, j], and the combined signal Z1 (Z, ZL) is predetermined. A gradation conversion apparatus characterized by substituting into a gain curve function k = k (Z1) to obtain a conversion gain k of a pixel [i, j]. The gradation converter according to claim 1,
The gain generation unit
The gradation conversion device, wherein the conversion gain k is decreased when the signal Z [i, j] is increased and is decreased when the signal ZL [i, j] is increased. The gradation converter according to any one of claims 1 to 3,
The signal Z [i, j] is a signal related to the luminance or brightness of the pixel [i, j]. The gradation converter according to any one of claims 1 to 3,
The signal Z [i, j] is a signal reflecting the brightness and saturation of the pixel [i, j], and shows a larger value as the saturation is higher even if the brightness is the same. A gradation converter characterized by that. The gradation converter according to any one of claims 1 to 5,
The signal ZL [i, j] is a signal obtained based on the brightness of the pixel [i, j] and a plurality of neighboring pixels of the pixel [i, j]. . The gradation converter according to claim 1,
The gain generation unit
(1) Signals X and XL are obtained by an operation for obtaining reciprocals of the signals Z and ZL,
(2) The signals X and XL are combined to generate a combined signal X1,
(3) Implement at least one of “gain limiter”, “power”, “gain reduction near 0”, and “gain closer to 1 when Z exceeds a predetermined value” with respect to the composite signal X1. A gradation conversion apparatus that performs processing h () to obtain the conversion gain k = h (X1). The gradation converter according to any one of claims 1 to 7,
The gradation converter
From the original image, a color signal C representing a quantity relating to color difference or saturation is obtained,
The color signal C is multiplied by a conversion gain k1 to generate a tone-converted color signal [where the conversion gain k1 is k1 = k · t (Z, where t (Z) is a monotonically changing function with respect to Z. Or k1 (Z, ZL) = k (t (Z), ZL)]
A gradation converter characterized by that.   A gradation conversion program for causing a computer to function as the signal acquisition unit, the neighborhood processing unit, the gain generation unit, and the gradation conversion unit according to any one of claims 1 to 8. A gradation converter according to any one of claims 1 to 8,
An imaging unit that images a subject and generates an original image;
An electronic camera, wherein the original image generated by the imaging unit is subjected to gradation conversion using the gradation conversion device. A gradation conversion method for converting the gradation of an original image,
Extracting or generating a signal Z [i, j] that changes according to at least the brightness of the pixel [i, j] of the original image;
Generating a signal ZL [i, j] that changes according to at least the brightness of a region near the pixel [i, j];
Determining a conversion gain k of a pixel [i, j] corresponding to the signal Z [i, j] and the signal ZL [i, j];
Performing gradation conversion by multiplying the conversion gain k of the pixel [i, j] by a color component of the pixel [i, j] or a signal component generated from the color component. Gradation conversion method.

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