JP2009004828A - Image processor, method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To individually adjust lightness of specified colors in an input image while reducing deterioration in saturation due to lightness conversion by effectively using a color reproduction range in an RGB color space. <P>SOLUTION: When an input color point X<SB>n</SB>is moved in the RGB color space, a lightness change amount calculation unit 5 moves the input color point X<SB>n</SB>obliquely in a direction wherein saturation increases more than in the linear direction from the input color point X<SB>n</SB>to a point W representing white color when the lightness of a pixel P<SB>n</SB>is smaller than the lightness of a lightness reference surface and a lightness adjustment amount Lit [H] of a reference hue [H] decided by a hue decision unit 3 indicates that an input image I<SB>0</SB>is made lighter, and moves the input color point X<SB>n</SB>obliquely in a direction wherein saturation increases more in the linear direction from the input color point X<SB>n</SB>to a point K representing black color when the lightness of the pixel P<SB>n</SB>is larger than the lightness of the lightness reference surface and the lightness adjustment amount Lit [H] of the reference hue [H] decided by the hue decision unit 3 indicates that the input image I<SB>0</SB>is made darker. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to image processing for performing image color adjustment, particularly brightness adjustment.

  There is a need to adjust only the brightness of a specific color when adjusting the color of a photographic image. Specifically, a specific color is adjusted to the user's preference, a specific subject is adjusted to a color stored by the user, or a reference print based on the color reproducibility of a photographic image It is conceivable to match the color.

  In response to such needs, in the RGB color space, the hue of each pixel in the input image is determined, and an input of the lightness conversion amount of the input image is received for each reference hue, and the determination result and the lightness conversion amount are determined. Thus, it has been proposed that the color point representing the position of each pixel in the input image in the RGB color space is linearly moved toward white or black, thereby correcting the brightness independently for each reference hue. (For example, Patent Document 1).

FIG. 15A and FIG. 15B schematically show the case where the brightness of R (red) is adjusted by the above method, and the end points of R, W (white), and K (black) are connected in the RGB color space. A triangle is represented. In order to brighten the color point P ₁ representing the position of the pixel in the input image in the RGB color space, the color point is moved in the linear direction from the point P ₁ to the point W as shown in FIG. 15A. If the point P _{2 is} to be darkened, the color point is moved in the linear direction from the point P ₂ to the point K as shown in FIG. 15B.
JP 2002-330300 A

  However, when the method described in Patent Document 1 is used, for example, the color reproduction range shown by shading in FIGS. 15A and 15B is not used, and thus an image with degraded saturation may occur.

  The present invention has been made in view of the above circumstances, and enables the individual color brightness in an input image to be individually adjusted while more effectively using the color reproduction range in the RGB color space. An object of the present invention is to provide an image processing apparatus, method and program.

  An image processing apparatus according to the present invention includes a lightness adjustment amount acquisition unit that receives an input of a lightness adjustment amount of at least one reference hue among a plurality of reference hues serving as a reference for a hue in an RGB color space, and a pixel in an input image Each time, based on the RGB value of the pixel, a hue determination unit that determines a reference hue whose contribution to the hue of the pixel is higher than a predetermined reference, and the brightness adjustment of the reference hue determined by the hue determination unit And a brightness conversion unit that moves an input color point that represents the position of the pixel in the RGB color space according to the amount, wherein the brightness conversion unit is configured such that the brightness of the pixel is greater than a predetermined brightness reference value. In the first case where the lightness adjustment amount of the reference hue determined by the hue determination means is small and represents that the input image is brightened, in the RGB color space, from the input color point Moving the input color point in a direction in which the saturation is larger than a direction toward the white point representing the color and in a direction in which the lightness of the pixel is increased, and the lightness of the pixel is greater than the lightness reference value, In the second case where the lightness adjustment amount of the reference hue determined by the hue determination unit represents that the input image is darkened, in the RGB color space, the direction from the input color point toward the black point representing black The input color point is moved in a direction in which the saturation is increased and the lightness of the pixel is decreased.

  The image processing method of the present invention accepts an input of an adjustment amount of lightness of at least one reference hue among a plurality of reference hues that serve as a hue reference in the RGB color space, and for each pixel in the input image, An image processing method for determining a reference hue whose contribution to the hue of the pixel is higher than a predetermined reference based on the RGB value, and moving the input color point according to the lightness adjustment amount of the determined reference hue In the first aspect, the lightness of the pixel is smaller than a predetermined lightness reference value when the input color point is moved, and the lightness adjustment amount of the reference hue determined to be the hue makes the input image brighter. In the RGB color space, the input color point is moved in a direction in which the saturation is larger than a direction from the input color point toward a white point representing white and in a direction in which the brightness of the pixel is increased, The pixel In a second case where the lightness is greater than the lightness reference value and the lightness adjustment amount of the determined reference hue represents darkening the input image, black representing black from the input color point in the RGB color space The input color point is moved in a direction in which the saturation is greater than the direction toward the point and in a direction in which the lightness of the pixel is reduced.

  An image processing program of the present invention causes a computer to execute the above-described image processing method.

  Details of the present invention will be described below.

  “A plurality of reference hues serving as hue references in the RGB color space” means primary colors in the RGB color space, that is, R (red), G (green), B (blue), and secondary colors, that is, C ( Cyan), M (magenta), Y (yellow).

  The “brightness adjustment amount” is a concept that includes the direction in which the brightness is adjusted, that is, the direction in which the brightness is increased or decreased, and the degree (amount) of adjustment in that direction.

  Specific examples of the method of “determining for each pixel in the input image a reference hue whose contribution to the hue of the pixel is higher than a predetermined reference” include the largest of the RGB values of the pixel, and The minimum complementary color may be determined as a reference hue higher than a predetermined reference that contributes to the hue of the pixel. In this case, the movement amount of the input color point is obtained for each of the determined reference hues, and the input color point is moved by the amount of the movement amount.

  The movement path of the input color point may be on a straight line or a curve.

  As a specific example of the method of moving the input color point, in the first case, the input color point is moved on a straight line passing through the input color point and the black point, and in the second case, the input color point and the white point are moved. It is conceivable to move on a straight line passing through.

  At this time, it is determined whether the lightness at the input color point crosses the lightness reference value at the time of movement, and if the lightness reference value is crossed at the first case, the input at the time of the movement After the intermediate color point where the lightness of the color point coincides with the lightness reference value, the color point is moved on a straight line from the intermediate color point to the white point, and when the lightness reference value is straddled in the second case, the movement is performed. In this case, after the intermediate color point, it is preferable to move on a straight line from the intermediate color point to the black point.

  The amount of movement of the input color point may be determined not only according to the lightness adjustment amount but also according to the height of the contribution of the reference hue determined for each pixel in the input image. It is conceivable to use the difference or ratio between the determined RGB value of the reference hue and the RGB value of the other reference hue to determine the “height of contribution”.

  As a specific example of the determination method of the magnitude relation between the brightness of each pixel and the brightness reference value, the input color point is perpendicular to the achromatic color axis connecting the white point and the black point, and the hue determination means It is determined that the lightness of the pixel is smaller than the lightness reference value when it is on the black point side with respect to the lightness reference plane passing through the end point of the determined reference hue, and the input color point is more than the lightness reference plane. It may be determined that the brightness of the pixel is greater than the brightness reference value when the pixel is on the white point side.

  Further, when the average value of the maximum and minimum RGB values of the pixel is smaller than the intermediate value between the maximum value and the minimum value that the RGB value can take in the input image, the brightness of the pixel is It may be determined that the lightness of the pixel is larger than the lightness reference value when it is determined that the lightness is smaller than the lightness reference value and the average value is larger than the intermediate value.

  Further, when the average value of the RGB values of the pixels is smaller than the intermediate value between the maximum value and the minimum value that can be taken by the RGB values in the input image, it is determined that the lightness of the pixels is smaller than the lightness reference value, When the average value is larger than the intermediate value, it may be determined that the lightness of the pixel is larger than the lightness reference value.

  According to the present invention, the input color point is moved in the RGB color space according to the input brightness adjustment amount and the reference hue determined to be high for each pixel in the input image. In this case, when the brightness of the pixel is smaller than a predetermined brightness reference value and the brightness adjustment amount of the reference hue determined to represent the hue indicates that the input image is to be brightened, white is represented from the input color point. The input color point is moved by tilting in a direction in which the saturation is larger than the direction toward the white point, the brightness of the pixel is greater than the brightness reference value, and the brightness adjustment amount of the determined reference hue is the input image. When the input color point is tilted in a direction in which the saturation is larger than the direction from the input color point toward the black point representing black, the color reproduction range in the RGB color space is reduced. Use more effectively It by while reducing the deterioration of saturation by brightness conversion, it is possible to adjust individually the specific brightness of the colors in the input image.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a hardware configuration of a digital photo print system including an image processing apparatus according to an embodiment of the present invention. As shown in the figure, this system includes a film scanner 51, a flat head scanner 52, a media drive 53, a network adapter 54, a display 55, a keyboard 56, a mouse 57, a hard disk 58, and a photo print output machine 59. 50 is connected.

  The arithmetic / control device 50 executes input of a program installed from a storage medium such as a CD-ROM, and cooperates with the CPU, main storage device, and various input / output interfaces in the device to input, correct, process and process images. It controls the flow of editing and output, and performs image correction, processing, and editing. Image processing for adjusting the brightness of an image according to the present invention is performed by this apparatus.

The film scanner 51 photoelectrically reads and digitizes APS negative film and 135 negative film that have been developed by a developing machine (not shown), and obtains digital image data I ₀ from the photographic images recorded on these negative films. To do.

Flat head scanner 52 is one in which digitized by reading a photograph image represented in hard copy, such as L-size photographic print photoelectrically obtains digital image data I _0.

The media drive 53 acquires digital image data I ₀ representing a photographic image recorded on a recording medium such as a memory card, CD, or DVD. It is also possible to write image data I ₁ after image processing on these recording media. For example, digital image data of an image obtained by photographing with a digital camera is written in the memory card. Further, for example, an image obtained by photographing with a digital camera or an image data of an image read by a film scanner at the previous print order is written on a CD, a DVD, or the like.

The network adapter 54 acquires the digital image data I ₀ from an order receiving machine (not shown) in a known network photo service system. The image data I ₀ is the image data based on the order of photographic prints from the user, is what has been sent over the Internet from the user's personal computer. Alternatively, it may be transmitted from a photo order accepting machine installed at a lab store.

  The display 55 displays an operation screen for image input, correction, processing / editing, and output in this system, and displays a menu for selecting operation contents, an image to be processed, and the like. A keyboard 56 and a mouse 57 are used to instruct processing contents.

The hard disk 58 stores programs and various parameters for controlling the system, and also includes image data I ₀ acquired by the film scanner 51, flat head scanner 52, media drive 53, and network adapter 54, and after image processing. The image data I _{1 is} also temporarily stored.

The photographic print output machine 59 performs scanning exposure, development, and drying on the photographic paper by the laser based on the image data I ₁ representing the image to be output, and also prints back information such as print information and print unit of the photographic paper. Cutting or sorting by order. The photographic printing method may be a laser exposure thermal development transfer method or the like.

  The flow of processing performed in this system is as follows.

First, the operator selects an input source by operating the keyboard 56 and the mouse 57 according to a screen for selecting the input source of the image data displayed on the display 55. The image data I ₀ is read from any one of the film scanner 51, the flat head scanner 52, and the media drive 53 in accordance with the selected input source. Further, in the case of an order by a network photo service system or a photo acceptance order machine at a store, the arithmetic / control device 50 receives the image data I ₀ via the network adapter 54. The image data I ₀ acquired in this way is temporarily stored in the hard disk 58.

Next, the image processing program executed by the arithmetic / control device 50 performs known white balance adjustment, contrast correction, sharpness correction, noise reduction / removal, and the like based on the setup conditions set in advance in the system. As necessary, image processing based on manual settings by the operator, including image brightness adjustment according to the present invention, and image processing / editing processing such as trimming and template composition are performed as necessary. Image data I ₁ is output. The output image data I ₁ is stored in the memory of the arithmetic / control device 50. Note that it may be temporarily stored in the hard disk 59.

Finally, according to the screen for selecting the output destination displayed on the display 55, the operator selects a desired output destination by operating the mouse 57 and the keyboard 56, and the arithmetic / control device 50 selects the selected output. The image data I ₁ is transmitted to the destination. When the photographic print output is performed, the image data I ₁ is transmitted to the photographic print output device 59, and an image based on the image data I ₁ is output as a photographic print. When outputting to a recording medium such as a CD, the image data I ₁ is written to a CD or the like set in the media drive 53.

FIG. 2 is a block diagram schematically illustrating the configuration of an image processing apparatus that adjusts the brightness of an image according to the first embodiment of the present invention. As shown in the figure, this image processing apparatus includes an image input unit 1 that receives input of image data I ₀ , R (red), G (green), B (blue), C (cyan), and M (magenta). -For each reference hue of Y (yellow), the brightness adjustment amount acquisition unit 2 that receives input of the brightness adjustment amount Lit [H] (H = R, G, B, C, M, Y) individually, and input image data I ₀ of the pixel _{P n (n = 1,2, ···} , n) for each, based on the RGB values of the pixel P _n, determine its contribution to the color of the pixel P _n is higher reference hue [H] For each pixel P _n of the input image data I ₀ , a hue coefficient CoefH [H] representing the height of contribution of the reference hue [H] determined by the hue determination unit 3 to the pixel P _{n is} calculated. For each pixel P _{n of} the hue coefficient calculation unit 4 to be calculated and the input image data I ₀ , for each pixel P _n according to the lightness adjustment amount Lit [H] of the reference hue [H] determined by the hue determination unit 3 RGB color space A lightness change amount calculation unit 5 for calculating the movement amount (lightness change amount) ΔRGB [H] of the color point X _n representing the position in the position, and the RGB value of each pixel P _n based on the lightness change amount ΔRGB [H]. The image conversion unit 6 converts the output image data I ₁ and outputs the output image data I _1. The functions of the processing units 1 to 6 execute a program installed in the arithmetic / control device 50 from a storage medium such as a CD-ROM. It is realized by.

  Next, the flow of image brightness adjustment processing by the image processing apparatus according to the first embodiment of the present invention and the processing units 1 to 6 of FIG. 2 are performed using the flowcharts of FIGS. 3A and 3B. Details of the processing will be described. In the following, it has an orthogonal coordinate system with R, G, B channels of each pixel of the input image data, and is normalized so that the minimum value of the signal value of each channel is 0 and the maximum value is 1. The description will be made on the premise of the RGB color space shown in FIG. In this RGB color space, the coordinates of W (white) are the origin (0,0,0), and R (red), G (green), B (blue), C (cyan), M (magenta), Y ( Yellow) and K (black) coordinates are (1,0,0), (0,1,0), (0,0,1), (0,1,1), (1,0, 1), (1,1,0), (1,1,1). Note that the normalization of the signal value is performed for convenience of explanation, and is not an essential process in the implementation of the present invention.

First, the image input unit 1 reads the image data I ₀ (# 1), and the brightness adjustment amount acquisition unit 2 includes the image based on the image data I ₀ and a brightness including a user interface for adjusting the brightness of the image. The adjustment screen is displayed on the display 55 (# 2). FIG. 4 is an example of a brightness adjustment screen. As shown in the figure, the brightness adjustment screen 20 is displayed on the reference hues of the image display areas 21, R, G, B, C, M, and Y for displaying images based on the image data I ₀ read by the image input unit 1. Are included, and slide buttons 22 to 27 for individually adjusting the brightness of the slide levers 22 and 27, and an execution button 28 for instructing execution of brightness adjustment processing based on the positions of the levers of the slide levers 22 to 27.

  When the operator moves the slide levers 22 to 27 of the brightness adjustment screen 20 using the keyboard 56 and the mouse 57, the brightness adjustment amount acquisition unit 2 determines the brightness adjustment amount of each reference hue based on the position of each lever. Lit [H] is calculated (# 3). Specifically, the lightness adjustment amount Lit [H] is determined based on a function or a reference table that defines the correspondence between the position amount of each lever and the lightness adjustment amount Lit [H]. In the present embodiment, the brightness adjustment amount Lit [H] takes a negative value when the brightness is reduced (darker), and the brightness adjustment amount Lit [H] takes a positive value when the brightness is increased (brighter). Shall.

Here, when the operator presses the execute button 28, first, a subscript n for identifying each pixel of the input image data I ₀ is set to 1 (# 4), and the first pixel P ₁ of the input image data I ₀ is set. RGB values are read (# 5).

The hue determination unit 3 compares the signal values of the read R, G, and B channels of the pixel P ₁ and identifies the maximum and minimum values.

Here, when the value of R is the maximum (# 6; YES), the hue determination unit 3 determines that one of the reference hues having a high contribution to the determination of the hue of the pixel P ₁ is R, and the hue The coefficient calculation unit 4 calculates the hue coefficient CoefH [R] (# 7). Specifically, it is calculated by the following equation (1).

CoefH [H] = 1-max (E, F) / D (1)
Here, H represents one of the reference hues R, G, and B, D represents the maximum value of R, G, and B of the pixel (here, the R channel signal value), and E and F represent the other channels. Represents the signal value of. From the above equation (1), the value of the hue coefficient CoefH [R] increases as the R channel signal value increases and as the G and B channel signal values decrease. FIG. 5A schematically shows the distribution of the value of the hue coefficient CoefH [H] for the channel having the maximum signal value on a regular hexagon representing the RGB color space. This regular hexagon represents a state in which a cube representing the RGB color space (see FIG. 7) is projected in a direction from point K to point W. Here, since the signal value of the R channel is the maximum (# 6; YES), attention is paid to the region surrounded by the point R and its neighboring points M and Y, and the point W representing the achromatic color axis (gray axis). As shown in FIG. 5A, the hue coefficient CoefH [R] increases as the color becomes darker, and the hue coefficient CoefH [R] decreases as the color becomes lighter.

Next, the lightness change amount calculation unit 5 calculates the lightness adjustment amount Lit [R] for the R channel acquired by the lightness adjustment amount acquisition unit 2 and the hue coefficient CoefH [R] calculated by the hue coefficient calculation unit 4. Then, the movement amount (brightness change amount) ΔRGB [R] of the color point X ₁ representing the position of the pixel P _{1 in} the RGB color space is calculated (# 8). At this time, the lightness change amount calculation unit 5 sets the achromatic color axis (gray axis) WK in the RGB color space as a normal vector, and on the point K side from the lightness reference plane passing through the points R, G, B, the color point X ₁ moving the color point X ₁ on a straight line passing through the preparative point K, at point W side than the brightness reference surface moves the color point X ₁ on a straight line passing through the color point X ₁ and the point W. For example, when the color point X ₁ is present in a triangle connecting the points W, K, and R in the RGB color space (shaded portion in FIG. 8A, FIG. 8B), the lightness change amount calculating unit 5 Control is performed so that the color point X ₁ moves on the broken line in the triangle WKR, and the movement amount (brightness change amount) ΔRGB [R] of the color point X ₁ is calculated. The details of the method of calculating the brightness change amount ΔRGB [H] will be described later.

When the hue determination unit 3 compares the signal values of the R, G, and B channels of the read pixel P ₁ and the G value is the maximum (# 9; YES), the hue of the pixel P ₁ It is determined that one of the reference hues that contributes to the determination of G is G, and the hue coefficient calculation unit 4 calculates the hue coefficient CoefH [G] in the same manner as in step # 7 (# 10), and the brightness change amount The calculation unit 5 calculates the brightness change amount ΔRGB [G] in the same manner as in step # 8 (# 11). Further, when the value of B is the maximum (# 12; YES), the hue determination unit 3 determines that one of the reference hues that contributes to the determination of the hue of the pixel P ₁ is B, and calculates the hue coefficient. The unit 4 calculates the hue coefficient CoefH [B] in the same manner as in step # 7 (# 13), and the brightness change amount calculating unit 5 calculates the brightness change amount ΔRGB [B] in the same manner as in step # 8. (#14).

Next, when the hue determination unit 3 compares the signal values of the R, G, and B channels of the read pixel P _{1 and} the R value is minimum (# 15; YES), the pixel P _One of the reference hues having a high contribution to the determination of the hue of 1 is determined to be C. The hue coefficient calculation unit 4 calculates the hue coefficient CoefH [C] by the following equation (2).

CoefH [H] = 1-max (1-E, 1-F) / (1-D) (2)
Here, H represents one of C, M, and Y of the reference hue, D represents the minimum value of R, G, and B of the pixel (here, the R channel signal value), and E and F represent the others. Represents the signal value of the channel. From the above equation (2), the value of the hue coefficient CoefH [C] increases as the R channel signal value decreases and the G and B channel signal values decrease. FIG. 5B schematically shows the distribution of the value of the hue coefficient CoefH [H] for the channel with the maximum signal value on a regular hexagon representing the same RGB color space as FIG. 5A. Here, since the signal value of the R channel is the smallest (# 15; YES), attention is paid to the area surrounded by the point C and the neighboring points G and B, and the point W representing the achromatic axis (gray axis). As shown in FIG. 5B, the hue coefficient CoefH [C] increases as the color becomes darker, and the hue coefficient CoefH [C] decreases as the color becomes lighter.

  The lightness change amount calculation unit 5 calculates the lightness change amount ΔRGB [C] in the same manner as in Step # 8 (# 17).

Further, when the value of G is minimum (# 18; YES), it is determined that one of the reference hues that contributes to the determination of the hue of the pixel P ₁ is M, and the hue coefficient calculation unit 4 performs step #. The hue coefficient CoefH [M] is calculated in the same manner as in 16 (# 19), and the lightness change amount calculation unit 5 calculates the lightness change amount ΔRGB [M] in the same manner as in step # 8 (# 20). Further, when the value of B is minimum (# 21; YES), the hue determination unit 3 determines that one of the reference hues that contributes to the determination of the hue of the pixel P ₁ is Y, and calculates the hue coefficient. The unit 4 calculates the hue coefficient CoefH [Y] in the same manner as in step # 16 (# 22), and the brightness change amount calculating unit 5 calculates the brightness change amount ΔRGB [Y] in the same manner as in step # 8. (#twenty three).

  The lightness change amount calculation unit 5 then adds the lightness change amounts ΔRGB [H] obtained in steps # 8, # 11, # 14, # 17, # 20, and # 23 (total lightness change amount) Δ Find RGB (# 24).

Image converting unit 6 adds the total brightness change amount △ RGB to RGB values of the pixel P _1, obtains the RGB value of the pixel after the conversion (# 25).

Then, accompanied by letter n 1 adds (# 26), if the value of n does not exceed the total number of pixels N of the input image data I ₀ (# 27; NO), the RGB values of the next pixel P _n Acquisition is performed (# 5), and the processing from step # 6 to # 25 is performed.

In this way, the RGB values after conversion are obtained for all the pixels by repeatedly performing the processing from step # 5 to step # 27 for all the pixels P ₁ to P _{n of} the input image data I ₀ , and n If the value exceeds the total number N of pixels of the input image data I ₀ (# 27; YES), the calculation / control device 50 uses the RGB value of each pixel after the conversion to convert the image data I ₁ after the brightness conversion. Is displayed on the display 55 (# 28).

  FIG. 6 is a flowchart showing details of the process for obtaining the lightness change amount ΔRGB [H] performed by the lightness change amount calculation unit 5.

Brightness correction amount calculation unit 5 first position of the color point X _n pixels P _n is determined whether the lower (point K side) than the brightness reference plane (# 31).

If the position of the color point X _n is below the brightness reference plane (# 31; YES), i.e. if the brightness of the color point X _n is smaller than the brightness in the brightness reference plane, each of the RGB color point X _n The color point _Xn is moved while maintaining the value ratio R: G: B (# 32). Specifically, _{assuming that} the RGB value of the color point X _n before the movement is (R, G, B), the RGB value (R1, G1, B1) of the color point after the movement is expressed by the following equation (3) to (5 ).
R1 = R + R / ave (R, G, B) * w1 * CoefH [H] * Lit [H] (3)
G1 = G + G / ave (R, G, B) * w1 * CoefH [H] * Lit [H] (4)
B1 = B + B / ave (R, G, B) * w1 * CoefH [H] * Lit [H] (5)
Here, ave (a, b, c) is an average value of a, b, c. Further, w1 is a weighting coefficient of the lightness change amount corresponding to the saturation of each pixel, and is obtained by the following equation (6).
w1 = max (R, G, B) −min (R, G, B) (6)
Accordingly, the lightness change amount calculation unit 5 can move the color point _Xn on the broken line in FIG. 9A.

On the other hand, when the position of the color point X _n is above the brightness reference plane (# 31; NO), that is, when the brightness of the color point X _n is greater than the brightness in the brightness reference plane, RGB color point X _n The color point _Xn is moved while maintaining the ratio (1-R) :( 1-G) :( 1-B) (# 33). Specifically, _{assuming that} the RGB value of the color point X _n before the movement is (R, G, B), the RGB value (R1, G1, B1) of the color point after the movement is expressed by the following equation (7) to (9 ).
R1 = R + (1-R) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H] * Lit [H] (7)
G1 = G + (1-G) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H] * Lit [H] (8)
B1 = B + (1-B) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H] * Lit [H] (9)
Accordingly, the lightness change amount calculation unit 5 can move the color point _Xn on the broken line in FIG. 9B.

Next, the lightness change amount calculation unit 5 determines whether or not the lightness reference plane is straddled during the above movement of the color point _Xn (# 34). After the movement direction of the color point _Xn after straddling the reference plane is switched, the position of the color point _Xn after the movement is obtained (# 35). Specifically, as shown in FIG. 10A, when the brightness reference plane is straddled in the direction in which the brightness increases, the direction from the passing point X ″ on the brightness reference plane when the color point X moves toward the point W 10B, when the brightness reference plane is straddled in the direction of decreasing brightness as shown in FIG. 10B, the passing point X ″ on the brightness reference plane when the color point X is moved is changed to the point K. The direction of movement is switched to the direction of heading.

In the case of FIG. 10A, the color point X _n (R, G, B) before the movement is moved to the point X _n ′ (R1, R1, G, B) on the straight line passing through the points K and X as described in step # 32. G1, B1), the passing point X _n ″ is (R2, G2, B2), and the final color point after movement after switching the moving direction from the passing point X _n ″ to the point W is X _n ′. Assuming '' (R3, G3, B3), _Xn '''(R3, G3, B3) can be obtained by the following equations (10) to (12).
R3 = R2 + (1-R2) / ave (1-R2,1-G2,1-B2) * w1 * CoefH [H] * Lit´ [H] (10)
G3 = G2 + (1-G2) / ave (1-R2,1-G2,1-B2) * w1 * CoefH [H] * Lit´ [H] (11)
B3 = B2 + (1-B2) / ave (1-R2,1-G2,1-B2) * w1 * CoefH [H] * Lit´ [H] (12)
Here, Lit ′ [H] is the brightness adjustment amount corresponding to the movement amount from the passing point X _n ″ (R2, G2, B2) to X _n ′ (R1, G1, B1) in the initial movement direction. Therefore, a value calculated as follows is used.

The movement from the passing point X _n ″ (R2, G2, B2) to X _n ′ (R1, G1, B1) is expressed by the following equations (13) to (15) using the above equations (3) to (5). It can be expressed as
R1 = R2 + R / ave (R, G, B) * w1 * CoefH [H] * Lit '[H] _R (13)
G1 = G2 + G / ave (R, G, B) * w1 * CoefH [H] * Lit '[H] _G (14)
B1 = B2 + B / ave (R, G, B) * w1 * CoefH [H] * Lit '[H] _B (15)
Here, the movement amounts R1-R2, G1-G2, and B1-B2 for each channel are set as ΔR1, ΔG1, and ΔB, respectively, and the above equations (13) to (15) are expressed as Lit ′ [H] _R and Lit ′. Solving for [H] _G and Lit ′ [H] _B , the following equations (13) ′ to (15) ′ are obtained.
Lit ′ [H] _R = △ R1 / (R / ave (R, G, B) * w1 * CoefH [H]) (13) ´
Lit ′ [H] _G = △ G1 / (G / ave (R, G, B) * w1 * CoefH [H]) (14) ´
Lit ′ [H] _B = △ B1 / (B / ave (R, G, B) * w1 * CoefH [H]) (15) ´
Therefore, as shown in the following equation (16), the average value of Lit ′ [H] _R , Lit ′ [H] _G , and Lit ′ [H] _B is defined as Lit ′ [H].

Lit´ [H] ＝ ave (Lit´ [H] _R , Lit´ [H] _G , Lit´ [H] _B ) (16)
On the other hand, in the case of FIG. 10B, the point after moving the color point X _n (R, G, B) before the movement on the straight line passing through the points W and X as described in step # 32 is X _n ′ ( R1, G1, B1), the passing point X _n ″ is (R2, G2, B2), and the final color point after the movement after switching the moving direction from the passing point X _n ″ to the point K is X _{Assuming n} ′ ″ (R3, G3, B3), X _n ′ ″ (R3, G3, B3) can be obtained from the following equations (17) to (19).
R3 = R2 + R2 / ave (R2, G2, B2) * w1 * CoefH [H] * Lit´ [H] (17)
G3 = G2 + G2 / ave (R2, G2, B2) * w1 * CoefH [H] * Lit´ [H] (18)
B3 = B2 + B2 / ave (R2, G2, B2) * w1 * CoefH [H] * Lit´ [H] (19)
Here, Lit ′ [H] is the brightness adjustment amount corresponding to the movement amount from the passing point X _n ″ (R2, G2, B2) to X _n ′ (R1, G1, B1) in the initial movement direction. And calculated using the following method.

The movement from the passing point X _n ″ (R2, G2, B2) to X _n ′ (R1, G1, B1) is expressed by the following equations (20) to (22) using the above equations (7) to (9). It can be expressed as
R1 = R2 + (1-R) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H] * Lit '[H] _R (20)
G1 = G2 + (1-G) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H] * Lit '[H] _G (21)
B1 = B2 + (1-B) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H] * Lit '[H] _B (22)
Here, the movement amounts R1-R2, G1-G2, and B1-B2 for each channel are set as ΔR1, ΔG1, and ΔB, respectively, and the above equations (20) to (22) are expressed as Lit ′ [H] _R and Lit ′. Solving for [H] _G and Lit ′ [H] _B , the following equations (20) ′ to (22) ′ are obtained.
Lit ′ [H] _R = △ R1 / ((1-R) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H]) (20) ′
Lit ′ [H] _G = △ G1 / ((1-G) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H]) (21) ′
Lit ′ [H] _B = △ B1 / ((1-B) / ave (1-R, 1-G, 1-B) * w1 * CoefH [H]) (22) ′
Therefore, as shown in the above equation (16), the average value of Lit ′ [H] _R , Lit ′ [H] _G , and Lit ′ [H] _B is defined as Lit ′ [H].

At the time of the movement of the color point X _n, if not across the lightness reference plane (# 34; NO), the processing of step # 35 is not performed.

The lightness change amount calculation unit 5 obtains the position after the movement of the color point X _n (R, G, B) as described above, and then calculates the lightness change amount ΔRGB [H] by the following equation (23). Calculate (# 36).

△ RGB [H] ＝ （R3-R, G3-G, B3-B） (23)
However, when the process of step # 35 is not performed, calculation is performed as R3 = R1, G3 = G1, B3 = B1.

As described above, according to the image processing apparatus that adjusts the brightness of an image according to the first embodiment of the present invention, the brightness change amount calculation unit 5 performs the process for each reference hue acquired by the brightness adjustment amount acquisition unit 2. The brightness adjustment amount Lit [H] (H = R, G, B, C, M, Y) and the hue determination unit 3 perform pixel P _n (n = 1, 2,..., N in the input image I _0. ) In accordance with the reference hue [H] that contributes to the hue of the pixel P _n determined every time, the brightness of the pixel P _{n is} the brightness when the input color point X _n is moved in the RGB color space. If the lightness adjustment amount Lit [H] of the reference hue [H] determined by the hue determination unit 3 is smaller than the brightness of the reference surface, it represents that the input image I ₀ is brightened, from the input color point X _n. The input color point _Xn is moved by tilting in a direction in which the saturation is larger than the direction toward the point W representing white, and the brightness of the pixel _Pn is greater than the brightness of the brightness reference plane. When the lightness adjustment amount Lit [H] of the reference hue [H] determined by the hue determination unit 3 indicates that the input image P _n is darkened, the input color point X _n is linear to the point K indicating black. The input color point _Xn is moved by tilting in a direction where the saturation is larger than the direction toward the color direction, so that the color reproduction range in the RGB color space can be used more effectively to reduce the deterioration of saturation due to lightness conversion. Meanwhile, it is possible to individually adjust the brightness of a specific color in the input image.

FIGS. 11 and 12 show an embodiment in the sRGB color space of the present invention. First, FIG. 11 shows an embodiment in which the brightness is increased, and the color change due to the adjustment of the brightness is represented in the L ^* a ^* b ^* color space. FIG. 11 (a) is plotted on a coordinate plane with L ^* as the vertical axis and c ^* as the horizontal axis, with ◯ before the brightness change and △ after the change, and by adjusting the brightness according to the present invention, It can be seen that the color reproduction range in the saturation direction is used more effectively. Similarly, FIG. 11B is plotted on a coordinate plane with b ^* as the vertical axis and a ^* as the horizontal axis, and the points are arranged on a straight line passing through the origin. It can be seen that the lightness adjustment according to the present invention does not affect the hue.

  FIG. 12 shows an example in which the brightness is lowered, and plotting is performed in the same manner as in FIG. In this case as well, as in the case where the brightness is increased, it can be seen from FIG. 12A that the color reproduction range in the saturation direction is more effectively used by adjusting the brightness according to the present invention. ), It can be seen that the lightness adjustment according to the present invention does not affect the hue.

In the above embodiment, as shown in FIG. 8B and the like, the lightness change amount calculation unit 5 moves the color point _Xn on a straight line passing the color point _Xn and the point K on the point K side from the lightness reference plane. is, but at point W side than the brightness reference plane had to move the color point X _n on a straight line passing through the color point X _n and the point W, as shown in FIG. 13, through the color point X _m, lightness The color point X _n may be moved on the parabola LP with the reference plane as the axis of symmetry.

  Further, the lightness reference plane is not a plane passing through the points R, G, and B with the achromatic color axis (gray axis) WK as a normal vector, and the average value of the maximum and minimum RGB values of the input pixels. If it is larger than a predetermined threshold (for example, 0.5), it may be determined that the input pixel is on the point W side from the brightness reference plane, and if it is smaller, the input pixel is on the point K side than the brightness reference plane. Moreover, you may use the average value of the RGB value of an input pixel instead of said average value.

  The image processing apparatus according to the second embodiment of the present invention generates a three-dimensional LUT (look-up table) based on the brightness adjustment amount for each reference hue input by the operator, and inputs the input image data into the 3 The brightness is adjusted by conversion using a dimension LUT. FIG. 14 is a block diagram schematically showing the configuration of the image processing apparatus. As shown in the figure, an input RGB value generation unit 11 and an LUT registration unit 12 are added to the image processing apparatus of the first embodiment shown in FIG. 2, and the processing flow between the blocks is changed. ing.

In the present embodiment, when the lightness adjustment amount acquisition unit 2 receives the setting of the lightness adjustment amount Lit [H] for each reference hue in the same manner as in the first embodiment, the input RGB value generation unit 11 receives the LUT in the LUT. A combination XL _n of input RGB values to be registered is sequentially generated. Here, if the input image is a combination of all values that the input image can take in the RGB color space, for example, an 8-bit image, (R, G, B) = (0,0,0) to (R 255, 255, 255) may be generated, or signal values may be added by a predetermined value (for example, 8), and (R, G, B) = (0,0,0), (0,0,8), (0,0,16), ..., (0,0,255), (0,8,0), ..., (255,255,255) Only combinations may be created.

The hue determination unit 3, the hue coefficient calculation unit 4, and the brightness change amount calculation unit 5 replace each RGB value combination XL _n generated by the input RGB value generation unit 11 instead of the RGB value of each pixel of the input data. As input, the same processing as in the first embodiment is performed.

LUT registration unit 12, for each combination XL _n of RGB values generated by the input RGB value generating unit 11, by adding the brightness changing amount △ RGB calculated for the XL _n the RGB values of the XL _n The output RGB value in the LUT is calculated, and the RGB value of XL _n is associated with the input RGB value and registered in the LUT.

For each pixel P _n of the input image data I ₀ input from the image input unit 1, the image conversion unit 6 refers to the LUT based on the RGB value of the pixel P _n and acquires the output RGB value after the brightness adjustment To do. Here, if all combinations that can be input RGB values are not registered in the LUT, the output RGB values corresponding to the input RGB values cannot be obtained when the LUT is referenced. Interpolation calculation using the registered contents of the LUT in the vicinity of the input RGB value may be performed. For example, if the RGB value of a pixel in the input image data is (0,0,100) and the input RGB values registered in the LUT are (0,0,96) and (0,0,104), Interpolation calculation is performed using the output RGB value associated with the input RGB value, and the RGB value after brightness adjustment for (0,0,100) is obtained.

  As described above, also in the image processing apparatus according to the second embodiment of the present invention, the same effect as in the first embodiment can be obtained. In the first embodiment, even when there are a plurality of pixels having the same RGB value in the input image data, the calculation of the same brightness change amount is repeated for each pixel. For the combination of values, the brightness change amount is calculated only once when registering in the LUT, so that the processing efficiency is improved.

  In addition to the above description, various modifications made to the system configuration, processing flow, table configuration, user interface, and the like in each embodiment without departing from the spirit of the present invention also apply to the technical scope of the present invention. include. Moreover, each said embodiment is an illustration to the last, and all the above-mentioned description should not be utilized in order to interpret the technical scope of this invention restrictively.

1 is a diagram schematically illustrating a hardware configuration of a digital photo print system including an image processing apparatus according to an embodiment of the present invention. 1 is a block diagram schematically illustrating a configuration of an image processing apparatus that performs image brightness adjustment according to a first embodiment of the present invention. The flowchart showing the flow of the brightness adjustment processing in the first embodiment of the present invention. Flowchart (Continued) showing a flow of brightness adjustment processing in the first embodiment of the present invention Figure showing an example of the brightness adjustment screen Diagram (R, G, B) schematically showing the distribution of hue coefficient values Diagram (C, M, Y) schematically showing the distribution of hue coefficient values Flow chart showing the detailed flow of brightness change amount calculation processing Schematic representation of RGB color space Diagram for explaining the lightness change amount calculation processing (RGB space and lightness adjustment plane) Diagram for explaining brightness change amount calculation processing (specific example) Diagram for explaining the lightness change amount calculation process (lightness adjustment below the lightness reference plane) Diagram for explaining the lightness change amount calculation processing (lightness adjustment on the upper side of the lightness reference plane) Diagram for explaining the lightness change amount calculation process (when the lightness is increased across the lightness reference plane) Diagram for explaining the lightness change amount calculation process (when lightness is lowered across the lightness reference plane) The figure which represented the Example of the brightness adjustment process of this invention typically (when the brightness is raised) The figure which represented the Example of the brightness adjustment process of this invention typically (when the brightness is lowered) The figure which represented typically another example of the movement path | route of the color point in the brightness adjustment process of this invention The block diagram which represented typically the structure of the image processing apparatus which performs the brightness adjustment of the image used as the 2nd Embodiment of this invention. Diagram for explaining brightness adjustment processing in the prior art (when increasing brightness) Diagram for explaining brightness adjustment processing in the prior art (when reducing brightness)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image input part 2 Lightness adjustment amount acquisition part 3 Hue determination part 4 Hue coefficient calculation part 5 Lightness change amount calculation part 6 Image conversion part 11 Input RGB value generation part 12 LUT registration part 50 Calculation and control apparatus 50
51 Film Scanner 52 Flat Head Scanner 53 Media Drive 54 Network Adapter 55 Display 56 Keyboard 57 Mouse 58 Hard Disk 59 Photo Print Output Machine

Claims (10)

A brightness adjustment amount acquisition means for receiving an input of a brightness adjustment amount of at least one reference hue among a plurality of reference hues serving as a reference of a hue in the RGB color space;
Hue determination means for determining, for each pixel in the input image, a reference hue whose contribution to the hue of the pixel is higher than a predetermined reference based on the RGB value of the pixel;
An image processing apparatus comprising: a lightness conversion unit that moves an input color point representing the position of the pixel in the RGB color space according to the lightness adjustment amount of the reference hue determined by the hue determination unit.
The brightness conversion means is
In the first case where the lightness of the pixel is smaller than a predetermined lightness reference value and the lightness adjustment amount of the reference hue determined by the hue determination means represents that the input image is brightened, in the RGB color space, Moving the input color point in a direction in which the saturation is larger than a direction from the input color point toward a white point representing white, and in a direction in which the brightness of the pixel is increased,
In the second case where the lightness of the pixel is larger than the lightness reference value and the lightness adjustment amount of the reference hue determined by the hue determination means represents that the input image is darkened, the input in the RGB color space An image processing apparatus, characterized in that the input color point is moved in a direction in which saturation is greater than a direction from a color point toward a black point representing black, and in a direction in which the brightness of the pixel is reduced. .   In the first case, the lightness conversion means moves on a straight line passing through the input color point and the black point, and in the second case, a straight line passing through the input color point and the white point. The image processing apparatus according to claim 1, wherein the image processing apparatus moves the top.   The lightness conversion means determines whether the lightness at the input color point crosses the lightness reference value during the movement, and if the lightness conversion means crosses the lightness reference value in the first case, In addition, after the intermediate color point where the lightness of the input color point coincides with the lightness reference value, it is moved on a straight line from the intermediate color point to the white point, and the lightness reference value is straddled in the second case. 3. The image processing apparatus according to claim 2, wherein after the intermediate color point is moved on a straight line from the intermediate color point to the black point during the movement.   The lightness conversion means determines the amount of movement of the input color point according to the lightness adjustment amount and the height of contribution of the reference hue determined by the hue determination means to the pixel. The image processing apparatus according to any one of claims 1 to 3. The hue determination means determines the maximum and minimum complementary colors of the RGB values of the pixel as a reference hue higher than a predetermined reference that contributes to the hue of the pixel;
The lightness conversion means obtains a movement amount of the input color point for each of the determined reference hues, and moves the input color point by an amount obtained by combining the movement amounts. Item 5. The image processing apparatus according to any one of Items 1 to 4.   The lightness conversion means includes a lightness reference plane in which the input color point is perpendicular to an achromatic color axis connecting the white point and the black point and passes through an end point of a reference hue determined by the hue determination means. When it is on the black point side, it is determined that the lightness of the pixel is smaller than the lightness reference value, and when the input color point is on the white point side with respect to the lightness reference plane, the lightness of the pixel is the lightness The image processing apparatus according to claim 1, wherein the image processing apparatus is determined to be larger than a reference value.   When the average value of the maximum and minimum RGB values of the pixel is smaller than the intermediate value between the maximum value and the minimum value that the RGB value can take in the input image, the lightness conversion means, The lightness of a pixel is determined to be smaller than the lightness reference value, and when the average value is larger than the intermediate value, the lightness of the pixel is determined to be larger than the lightness reference value. Item 6. The image processing apparatus according to any one of Items 1 to 5.   When the average value of the RGB values of the pixels is smaller than the intermediate value between the maximum value and the minimum value that the RGB values can take in the input image, the lightness conversion means has a lightness of the pixels that is smaller than the lightness reference value. The brightness of the pixel is determined to be greater than the brightness reference value when the average value is greater than the intermediate value. The image processing apparatus described. Receiving an input of an adjustment amount of lightness of at least one reference hue among a plurality of reference hues serving as a hue reference in the RGB color space;
For each pixel in the input image, based on the RGB value of the pixel, determine a reference hue whose contribution to the hue of the pixel is higher than a predetermined reference,
In the image processing method of moving the input color point according to the lightness adjustment amount of the determined reference hue,
In the first case, when the input color point is moved, the lightness of the pixel is smaller than a predetermined lightness reference value, and the lightness adjustment amount of the reference hue whose hue is determined represents that the input image is brightened. In the RGB color space, the input color point is moved in a direction in which the saturation is larger than a direction from the input color point toward a white point representing white, and in a direction in which the brightness of the pixel is increased,
In a second case where the lightness of the pixel is greater than the lightness reference value and the lightness adjustment amount of the determined reference hue represents darkening the input image, a black color from the input color point in the RGB color space An image processing method, wherein the input color point is moved in a direction in which the saturation is larger than a direction toward the black point representing the color and in a direction in which the lightness of the pixel is smaller. On the computer,
Receiving an input of an adjustment amount of lightness of at least one reference hue among a plurality of reference hues serving as a hue reference in the RGB color space;
For each pixel in the input image, based on the RGB value of the pixel, determine a reference hue whose contribution to the hue of the pixel is higher than a predetermined reference,
In an image processing program for executing processing for moving the input color point according to the lightness adjustment amount of the determined reference hue,
When causing the computer to execute the process of moving the input color point, the brightness of the pixel is smaller than a predetermined brightness reference value, and the brightness adjustment amount of the reference hue determined to be hued makes the input image brighter. In the RGB color space, the input color in a direction in which the saturation is larger than the direction from the input color point toward the white point representing white, and in the direction in which the brightness of the pixel is increased. Move the point,
In a second case where the lightness of the pixel is greater than the lightness reference value and the lightness adjustment amount of the determined reference hue represents darkening the input image, the input color point is blackened from the input color point in the RGB color space. An image processing program for executing a process of moving the input color point in a direction in which the saturation is larger than a direction toward a black point representing the color and in a direction in which the brightness of the pixel is smaller.