JP4111689B2 - Image processing apparatus, computer-readable recording medium storing image processing program, and program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus, a computer-readable recording medium on which an image processing program is recorded, and a program, and more particularly to an image processing apparatus and an image processing program capable of sharpening without changing the hue of a color image. The present invention relates to a computer-readable recording medium and a program.
[0002]
[Prior art]
In general, in a process for sharpening a blurred image, an edge enhancement process for enhancing a high-frequency region of image data is performed. If the input image is a monochrome image, this process can be used to sharpen a blurred image. However, when the input image is a color image, if the edge enhancement processing is simply performed on each color component such as RGB (red, green, blue) and CMY (cyan, magenta, yellow), the same as the monochrome image. Although it becomes a clear image, since the hue and saturation of the edge portion change, the hue changes compared to the original image. For example, in an image in which black and blue lines intersect with a white background, an original color may appear, for example, the boundary between the black and blue lines becomes yellow.
[0003]
In televisions, video cameras, and the like, a technique is generally used in which a color image is converted into a luminance component and a color difference component, and sharpening is performed by performing edge enhancement processing on the luminance component. By this method, it is possible to sharpen a natural image or the like relatively well. However, for example, in an image where red and blue lines are written on a white background, the red and blue luminance components are small, so the edge enhancement process may change the color of the red and blue lines to black. . Conversely, a colored line drawn in a dark background may be lightened by edge enhancement processing.
[0004]
In order to solve such a problem, the edge enhancement processing apparatus for color gradation image information disclosed in Japanese Patent Application Laid-Open No. 61-273073 extracts brightness from input image data and performs edge enhancement on the brightness. Perform processing. A correction coefficient is obtained from the result, and sharpening is performed by multiplying each color component (cyan (C), magenta (M), yellow (Y)) of the input image data by the correction coefficient. In this method, C component, M component, and Y component are respectively multiplied by the same coefficient. For this reason, sharpening can be performed without shifting the hue of input and output.
[0005]
[Problems to be solved by the invention]
However, the C component, M component, and Y component are finite values. For this reason, when scaling processing is performed based on lightness, the value becomes 0 or becomes saturated. As a result, the image becomes whitish or blackish, and the saturation changes.
[0006]
Further, when only the saturation or hue changes without changing the brightness, edge enhancement cannot be performed.
[0007]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to satisfactorily sharpen an input image having no change in brightness without changing the hue of the input image. An image processing apparatus, a computer-readable recording medium on which an image processing program is recorded, and a program are provided.
[0009]
[Means for Solving the Problems]
  An image processing apparatus according to an aspect of the present invention sharpens a color image. Image data is expressed by hue, saturation, and brightness. The image processing apparatus is connected to the saturation edge enhancement means for enhancing the saturation edge of the image data, the brightness edge enhancement means for enhancing the brightness edge of the image data, and the saturation edge enhancement means, Saturation correction means for correcting the saturation output from the saturation edge enhancement means based on the saturation of the image data before edge enhancement.The saturation correction means compares the saturation of the image data after edge enhancement by the saturation edge enhancement means with the saturation of the image data before edge enhancement, and the saturation of the image data after edge enhancement is before the edge enhancement. When the rate of change from the saturation of the image data is greater than a predetermined rate, the saturation of the image data after edge enhancement is corrected so as to be within the predetermined rate.
[0010]
  No processing is performed on the hue of the image data, and edge enhancement processing is performed only for lightness and saturation. For this reason, sharpening can be performed while maintaining the color of the original image. Also, edge enhancement is performed not only for lightness but also for saturation. For this reason, it is possible to sharpen even an image having no change in brightness.The saturation correction unit is configured to reduce the saturation of the image data after the saturation edge enhancement so that the ratio at which the saturation of the image data after the saturation edge enhancement changes from the saturation of the image data before the edge enhancement falls within a predetermined ratio. Correct. For this reason, it is possible to prevent the occurrence of whiteout (locally white points) and unintended colors due to extreme changes in saturation.
[0011]
  Preferably, the image processing apparatus further includes first conversion means for converting image data in which each pixel is represented by coordinates in a predetermined color space into image data represented by hue, saturation, and brightness. . The saturation edge enhancement means includes means for enhancing the saturation edge of the image data connected to the first conversion means and output from the first conversion means. The lightness edge enhancement means includes means for enhancing the lightness edge of the image data output from the first conversion means and connected to the first conversion means. The saturation correction unit is connected to the first conversion unit and the saturation edge enhancement unit, and is output from the first conversion unit.Before edge enhancementBased on the saturation of the image data, output from the saturation edge enhancement meansImage data after edge enhancementMeans for correcting saturation;
[0012]
More preferably, the image processing apparatus is further connected to the first conversion unit, the saturation correction unit, and the brightness edge enhancement unit, and the hue output from the first conversion unit and the saturation output from the saturation correction unit. Image data represented by brightness output from the brightness and brightness edge enhancement means includes second conversion means for converting the image data into coordinates in a predetermined color space.
[0013]
  More preferably, the saturation correction means is edge enhancement.Of previous image dataOnly if the saturation is less than a predetermined value,saturationOutput from edge enhancement meansImage data after edge enhancementThe saturation is allowed to be smaller than the saturation of the image data before edge enhancement.
[0014]
For this reason, it is possible to prevent the edge portion from changing to white. Accordingly, the originally whitish part can be emphasized whiter.
[0023]
More preferably, the color space represented by hue, saturation, and lightness is represented by a hexagonal pyramid color model.
[0024]
In the hexagonal pyramid color model, the brightness is the maximum value of the R (red) value, the G (green) value, and the B (blue) value. For this reason, for example, even in an image in which a red blurred line is drawn on a white background, there is no change in lightness, so that the color does not change to black due to edge enhancement for lightness.
[0029]
  A computer-readable recording medium according to still another aspect of the present invention includes a step of enhancing an edge of saturation of image data, a step of enhancing an edge of lightness of image data, and the saturation of image data before edge enhancement. To correct the saturation of the image data after edge enhancementSaturation correctionAn image processing program for causing a computer to execute the steps is recorded.In the saturation correction step, the saturation of the image data after edge enhancement by the step of enhancing the edge of saturation is compared with the saturation of the image data before edge enhancement. When the rate of change from the saturation of the image data before enhancement is greater than a predetermined rate, the saturation of the image data after edge enhancement is corrected so as to be within the predetermined rate.
[0030]
  No processing is performed on the hue of the image data, and edge enhancement processing is performed only for lightness and saturation. For this reason, sharpening can be performed while maintaining the color of the original image. Also, edge enhancement is performed not only for lightness but also for saturation. For this reason, it is possible to sharpen even an image having no change in brightness.In the saturation correction step, the saturation of the image data after saturation edge enhancement is adjusted so that the ratio of the saturation of the image data after saturation edge enhancement changes from the saturation of the image data before edge enhancement falls within a predetermined ratio. Correct. For this reason, it is possible to prevent the occurrence of whiteout (locally white points) and unintended colors due to extreme changes in saturation.
[0033]
  According to still another aspect of the present invention, there is provided a program based on a step of enhancing a saturation edge of image data, a step of enhancing a brightness edge of image data, and a saturation of image data before edge enhancement. To correct the saturation of the image data after edge enhancement.Saturation correctionIs a program for executing steps.In the saturation correction step, the saturation of the image data after edge enhancement by the step of enhancing the edge of saturation is compared with the saturation of the image data before edge enhancement. When the rate of change from the saturation of the image data before enhancement is larger than the predetermined rate, the saturation of the image data after edge enhancement is corrected so as to be within the predetermined rate..
[0034]
  No processing is performed on the hue of the image data, and edge enhancement processing is performed only for lightness and saturation. For this reason, sharpening can be performed while maintaining the color of the original image. Also, edge enhancement is performed not only for lightness but also for saturation. For this reason, it is possible to sharpen even an image having no change in brightness.In the saturation correction step, the saturation of the image data after saturation edge enhancement is adjusted so that the ratio of the saturation of the image data after saturation edge enhancement changes from the saturation of the image data before edge enhancement falls within a predetermined ratio. Correct. For this reason, it is possible to prevent the occurrence of whiteout (locally white points) and unintended colors due to extreme changes in saturation.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0038]
[First Embodiment]
Referring to FIG. 1, an image processing apparatus according to a first embodiment of the present invention includes a computer main body 1, a graphic display device 2, an FD drive 3 on which an FD (Flexible Disc) 4 is mounted, and a keyboard. 5, a mouse 6, a CD-ROM device 7 to which a CD-ROM (Compact Disc-Read Only Memory) 8 is mounted, a network communication device 9 for transmitting and receiving data to and from an external computer over a network, and a computer body 1, a graphic display device 2, an FD drive 3, a keyboard 5, a mouse 6, a CD-ROM device 7, and a network communication device 9.
[0039]
The computer main body 1 includes a central processing unit (CPU) 10, a read only memory (ROM) 11, a random access memory (RAM) 12, and a hard disk 13.
[0040]
The CPU 10 performs processing while inputting / outputting data to / from the graphic display device 2, FD drive 3, keyboard 5, mouse 6, CD-ROM device 7, network communication device 9, ROM 11, RAM 12 or hard disk 13. The image processing program recorded on the FD 4 or the CD-ROM 8 is temporarily stored in the hard disk 13 by the CPU 10 via the FD live 3 or the CD-ROM device 7. The CPU 10 executes processing on the image data stored in the RAM 12 by appropriately loading an image processing program from the hard disk 13 into the RAM 12 and executing it. The image processing program may be supplied to the computer main body 1 from the network communication device 9 via a communication line from another computer.
[0041]
With reference to FIG. 2, the functional configuration of the image processing apparatus according to the present embodiment will be described. An image processing apparatus includes an HSI conversion unit that converts image data including three components of red (R), green (G), and blue (B) into hue (H), saturation (S), and brightness (I). 20 and an edge enhancement unit 21 connected to the HSI conversion unit 20 for edge enhancement in saturation and lightness, and a saturation connected to the HSI conversion unit 20 and the edge enhancement unit 21 for correcting the edge-enhanced saturation. HSI inverse connected to the correction unit 22, the HSI conversion unit 20, the edge enhancement unit 21, and the saturation correction unit 22 to convert the values of the H component, the S component, and the I component into the values of the R component, the G component, and the B component. A conversion unit 23.
[0042]
The format of input / output image data is not limited to the RGB format, but may be a CMY format. Further, the format may be different between the input and the output, for example, the input is RGB format and the output is CMY format.
[0043]
HSI may be expressed as HSV (hue, saturation, brightness) or HSL (hue, saturation, brightness), but the meanings are the same.
[0044]
Processing executed by the image processing apparatus will be described with reference to FIG.
The HSI converter 20 converts the input image data into HSI format image data (S1). The edge enhancement unit 21 performs edge enhancement processing on the S component and the I component (S2). The saturation correction unit 22 corrects the edge-enhanced saturation (S) (S3). The HSI inverse conversion unit 23 converts the image data composed of the H component output from the HSI conversion unit 20, the S component output from the saturation correction unit 22 and the I component output from the edge enhancement unit 21 into RGB image data. And output (S4). A conversion method from the RGB format to the HSI format and a reverse conversion method from the HSI format to the RGB format are known techniques. Therefore, detailed description thereof will not be repeated here.
[0045]
The relationship between the HSI space and the RGB space is shown with reference to FIG. 4, FIG. 5, and FIG. Thereby, the relationship between the RGB format value and the HSI format value is shown, and the processing of S1 and S4 in FIG. 3 is realized.
[0046]
In this embodiment, an HSI 6 pyramid color model is used as a model representing the HSI space. The HSI 6 pyramid color model is generally used as described in detail on pages 486 to 489 in the “Image Analysis Handbook” (Tokyo University Press), supervised by Mikio Takagi and Yoji Shimoda, published on January 17, 1991. Color model.
[0047]
Considering a cube in contact with the three axes in the RGB orthogonal coordinate system, R, G, B and their complementary colors C, M, Y have a positional relationship as shown in FIG. The main diagonal axis of the RGB cube is defined as the brightness axis I. Then, a hexagonal pyramid color model as shown in FIG. 5 is obtained. The brightness of a point P in the hexagonal pyramid color model is defined as the maximum value of the R value, G value, and B value of the point P. FIG. 6 shows a plane passing through the point P and orthogonal to the lightness axis I. Hue (H) is defined as the angle between WR and WP, where W is the point where lightness axis I intersects its plane, and saturation (S) is WP, where E is the intersection of the extension line of WP and the hexagon. / WE. The model representing the HSI space may be another model.
[0048]
With reference to FIG. 7, the process of S2 of FIG. 3 will be described. FIG. 7 shows each coefficient of the edge enhancement filter. a is a parameter for adjusting the strength of edge enhancement. Edge enhancement of the pixel of interest can be obtained by subtracting the values of the pixels in the vicinity of the surrounding 8 from the result of multiplying the value of the pixel of interest by (a + 1), respectively (a / 8). In the case of saturation edge enhancement, the S component is used as the pixel value, and in the case of lightness edge enhancement, the I component is used as the pixel value. Note that the result of the filtering process is limited by the range of each component. By this filter processing, changes in saturation and lightness are emphasized.
[0049]
With reference to FIG. 8, the process (saturation correction) of S3 in FIG. 3 will be described. The saturation before edge enhancement is S0, the saturation after edge enhancement is S1, and the saturation after saturation correction is S2. The saturation correction unit 22 compares the values of S1 and S0 (S10). If S1 is larger than S0 (YES in S10), the value obtained by multiplying S0 by 1.5 and the smaller value of S1 are used. S2 is set (S11). When S1 is smaller than S0 (NO in S10, YES in S12), if S0 is 0.2 or less (YES in S13), S1 is set to S2 (S14). In cases other than the above, S0 is set to S2 (S15).
[0050]
As described above, only when the original saturation is small (NO in S10, YES in S12, and YES in S13), the reduction of the saturation due to the processing of the edge enhancement unit 21 is allowed (S14). For this reason, it is possible to prevent the edge portion from changing to white. Accordingly, the originally whitish part can be emphasized whiter. Further, by limiting the rate of increase in saturation (S11), it is possible to prevent unintended colors from appearing in portions that are not originally colored.
[0051]
[Variation 1 of saturation correction]
With reference to FIG. 9, another saturation correction process in the saturation correction unit 22 will be described. When the saturation S1 after edge enhancement is larger than the saturation S0 before edge enhancement (YES in S20), the value obtained by multiplying S0 by 1.5 and the smaller one of S1 are corrected. (S21), otherwise, the larger of S0 and S1, the larger value of S1, is set to S2 (S22).
[0052]
[Variation 2 of saturation correction]
With reference to FIG. 10, still another saturation correction process in the saturation correction unit 22 will be described. When S1 is larger than S0 (YES in S25), the value obtained by adding 0.1 to S0 and the smaller value of S1 is set to S2 (S26). Otherwise, 0.1 is subtracted from S0. The larger value of S1 and S1 is set as S2 (S27).
[0053]
Both Modifications 1 and 2 have the same effect as the processing shown in FIG.
As described above, according to the image processing apparatus of the present embodiment, the hue is not processed, and only the brightness and saturation are sharpened. For this reason, sharpening can be performed while maintaining the color of the original image. Further, since edge enhancement is performed not only for lightness but also for saturation, sharpening can be performed even for an image having no change in lightness.
[0054]
In saturation correction, the rate or amount of change in saturation is limited. For this reason, it is possible to prevent occurrence of whiteout and unintended colors due to extreme changes in saturation.
[0055]
In the HSI 6 pyramid color model, the brightness is the maximum value of the R value, the G value, and the B value. For this reason, for example, even in an image in which a red blurred line is drawn on a white background, there is no change in lightness, so that the color does not change to black due to edge enhancement for lightness. Furthermore, since edge enhancement is performed on the saturation, the blurred pixel changes to white or red, and sharpening can be performed satisfactorily.
[0056]
[Second Embodiment]
The schematic hardware configuration of the image processing apparatus according to the second embodiment of the present invention is the same as that of the image processing apparatus according to the first embodiment shown in FIG. Therefore, detailed description thereof will not be repeated here.
[0057]
With reference to FIG. 11, a functional configuration of the image processing apparatus in the present embodiment will be described. The image processing apparatus includes an HS extraction unit 30 that extracts hue (H) and saturation (S) from input image data including three components of red (R), green (G), and blue (B), and an input image. The edge enhancement unit 31 that performs edge enhancement on the R component, G component, and B component of the data, and the edge-enhanced input image data that is connected to the edge enhancement unit 31 are H (hue) and S (saturation). Are connected to the HSI conversion unit 32 that converts to I (lightness), the HS extraction unit 30 and the HSI conversion unit 32, and corrects the hue of the image after edge enhancement based on the hue output from the HS extraction unit 30. A hue correction unit 33, and a saturation correction unit 34 that is connected to the HS extraction unit 30 and the HSI conversion unit 32 and corrects the saturation of the image after edge enhancement based on the saturation output from the HS extraction unit 30; , Hue correction unit 33, It is connected to the reduced native code storage region 34 and the HSI converting section 32, including H component value R component of the S component and I component and HSI inverse transformation unit 35 for converting the value of the G component and the B component.
[0058]
The format of input / output image data is not limited to the RGB format, but may be a CMY format. Further, the format may be different between the input and output, for example, the input is RGB format and the output is CMY format.
[0059]
Further, the input / output data may be in the HSI format. In this case, the HSI conversion unit 32 and the HSI inverse conversion unit 35 output the input data without doing anything.
[0060]
Processing executed by the image processing apparatus will be described with reference to FIG.
The HS extraction unit 30 extracts an H (hue) component and an S (saturation) component from the input image data (S30). The edge enhancement unit 31 performs edge enhancement processing on each of the R component, G component, and B component of the input image data (S31). The HSI converter 32 converts edge-enhanced RGB format image data into HSI format image data (S32). The hue correction unit 33 corrects the hue after edge enhancement based on the hue before edge enhancement (S33). The saturation correction unit 34 corrects the saturation after edge enhancement based on the saturation before edge enhancement (S34). The HSI inverse conversion unit 35 converts the image data composed of the H component output from the hue correction unit 33, the S component output from the saturation correction unit 34, and the I component output from the HSI conversion unit 32 into RGB format image data. (S35). A conversion method from the RGB format to the HSI format and a reverse conversion method from the HSI format to the RGB format are known techniques. Therefore, detailed description thereof will not be repeated here.
[0061]
The HS extraction unit 30 executes a process of extracting the H component and the S component from the RGB format image. This processing is a known technique as described above. Therefore, detailed description thereof will not be repeated here.
[0062]
The edge enhancement unit 31, the HSI conversion unit 32, and the HSI inverse conversion unit 35 perform the same processing as the edge enhancement unit 21, the HSI conversion unit 20, and the HSI inverse conversion unit 23 of FIG. Therefore, detailed description thereof will not be repeated here.
[0063]
The saturation correction unit 34 performs the same processing as the saturation correction unit 22 of FIG. Therefore, detailed description thereof will not be repeated here. Note that the saturation S0 in the saturation correction unit 22 corresponds to the saturation S output from the HS extraction unit 30, and the saturation S1 corresponds to the saturation output from the HSI conversion unit 32.
[0064]
With reference to FIG. 13, the process (hue correction) in S33 of FIG. 12 will be described. The hue before edge enhancement is H0, the hue after edge enhancement is H1, and the hue after hue correction is H2. The hue correction unit 33 compares the values of H1 and H0 (S40), and if H1 is greater than H0 (YES in S40), the value obtained by adding 5 to H0 and the smaller value of H1 to H2 (S41). When H1 is equal to or lower than H0 (NO in S40), a value obtained by subtracting 5 from H0 and a larger value of H1 is set as H2 (S42). The hue is an angle and takes a value from 0 to 360. Further, there is a relationship of H = H ± 360.
[0065]
As described above, according to the image processing apparatus of the present embodiment, the hue change at the time of edge enhancement is limited by the hue correction process. For this reason, it is possible to prevent the input image from changing to an unintended color by the edge enhancement process, and it is possible to sharpen the image while maintaining the hue of the original image. Further, since a certain amount of hue change is recognized, sharpening can be performed even for an image having no change in saturation and lightness.
[0066]
Further, since edge enhancement is performed on each color component of the input image data, it is possible to sharpen even image data with a constant saturation as well as lightness.
[0067]
  Furthermore, the saturation correction process limits the change in saturation during edge enhancement. For this reason, it is possible to prevent occurrence of whiteout and unintended colors due to extreme changes in saturation.
  An image processing method according to still another aspect of the present invention sharpens a color image. The image processing method includes a step of enhancing the saturation edge of the image data, a step of enhancing the brightness edge of the image data, and the image data after edge enhancement based on the saturation of the image data before edge enhancement. Correcting the saturation.
  No processing is performed on the hue of the image data, and edge enhancement processing is performed only for lightness and saturation. For this reason, sharpening can be performed while maintaining the color of the original image. Also, edge enhancement is performed not only for lightness but also for saturation. For this reason, it is possible to sharpen even an image having no change in brightness.
  An image processing method according to still another aspect of the present invention sharpens a color image. The image processing method includes a step of extracting a hue from image data in which each pixel value is represented by predetermined coordinates, a step of extracting a saturation from the image data, and enhancing an edge of the image data for each color component. Converting the image data in which the edge is emphasized into image data represented by hue, saturation and brightness, correcting the hue after edge enhancement based on the hue before edge enhancement, Correcting the saturation after edge enhancement based on the saturation before edge enhancement.
  Edge enhancement is performed on each color component of the input image data. For this reason, sharpening can be performed not only for lightness but also for image data with a constant saturation.
  An image processing apparatus according to another aspect of the present invention sharpens a color image. An image processing apparatus includes a hue extraction unit for extracting a hue from image data in which each pixel value is represented by coordinates in a predetermined color space, and a saturation extraction unit for extracting a saturation from the image data. And color component emphasizing means for emphasizing the edge of the image data for each color component, and image data that is connected to the color component emphasizing means and has the edge enhanced by the color component emphasizing means, by hue, saturation, and brightness A first conversion means for converting the image data to be represented, a hue extraction means and a first conversion means, and output from the first conversion means based on the hue output from the hue extraction means; Saturation output from the first conversion means based on the saturation output from the saturation extraction means connected to the hue correction means for correcting the hue, the saturation extraction means and the first conversion means For correcting And a degree correction means. The hue correction unit compares the hue of the image data after edge enhancement output from the first conversion unit with the hue of the image data before edge enhancement output from the hue extraction unit, and compares the hue of the image data after edge enhancement. When the rate at which the hue changes from the hue of the image data before edge enhancement is greater than a predetermined rate, the hue of the image data after edge enhancement is corrected so as to be within the predetermined rate. The saturation correction unit compares the saturation of the image data after edge enhancement output from the first conversion unit with the saturation of the image data before edge enhancement output from the saturation extraction unit, and after edge enhancement. When the rate at which the saturation of the image data changes from the saturation of the image data before edge enhancement is greater than a predetermined rate, the saturation of the image data after edge enhancement is corrected so as to fall within the predetermined rate.
  Edge enhancement is performed on each color component of the input image data. For this reason, sharpening can be performed not only for lightness but also for image data with a constant saturation. The hue correction unit corrects the hue of the image data after edge enhancement so that the ratio at which the hue of the image data after edge enhancement changes from the hue of the image data before edge enhancement falls within a predetermined ratio. For this reason, it is possible to prevent the input image from changing to an unintended color by the edge enhancement process, and it is possible to sharpen the image while maintaining the hue of the original image. The saturation correction unit corrects the saturation of the image data after edge enhancement so that the ratio at which the saturation of the image data after edge enhancement changes from the saturation of the image data before edge enhancement falls within a predetermined ratio. For this reason, it is possible to prevent the occurrence of whiteout (locally white points) and unintended colors due to extreme changes in saturation.
  Preferably, the image processing apparatus is further connected to a hue correction unit, a saturation correction unit, and a first conversion unit, and the hue output from the hue correction unit and the saturation output from the saturation correction unit. And second conversion means for converting the lightness output from the first conversion means into coordinates in a predetermined color space.
  More preferably, the saturation correction means is the edge output from the first conversion means only when the saturation of the image data before edge enhancement output from the saturation extraction means is smaller than a predetermined value. The saturation of the image data after enhancement is allowed to be smaller than the saturation of the image data before edge enhancement outputted from the saturation extraction means.
  For this reason, it is possible to prevent the edge portion from changing to white. Accordingly, the originally whitish part can be emphasized whiter.
  A computer-readable recording medium according to still another aspect of the present invention extracts a hue from image data in which each pixel value is represented by coordinates in a predetermined color space, and extracts saturation from the image data. A step of enhancing the edge of the image data for each color component, a step of converting the image data in which the edge is enhanced into image data represented by hue, saturation, and brightness, and before edge enhancement Image processing that causes a computer to execute a hue correction step for correcting the hue after edge enhancement based on the hue of the image and a saturation correction step for correcting the saturation after edge enhancement based on the saturation before edge enhancement The program is recorded. The hue correction step compares the hue of the image data after edge enhancement outputted from the image data conversion step with the hue of the image data before edge enhancement outputted from the step of extracting the hue, and the image data after edge enhancement When the rate at which the hue of the image data changes from the hue of the image data before edge enhancement is greater than a predetermined rate, the hue of the image data after edge enhancement is corrected so as to fall within the predetermined rate. The saturation correction step compares the saturation of the edge-enhanced image data output from the image data conversion step with the saturation of the image data before the edge enhancement output from the step of extracting saturation, and performs edge enhancement. When the rate at which the saturation of the subsequent image data changes from the saturation of the image data before edge enhancement is greater than a predetermined rate, the saturation of the image data after edge enhancement is corrected so that it falls within the predetermined rate. .
  Edge enhancement is performed on each color component of the input image data. For this reason, sharpening can be performed not only for lightness but also for image data with a constant saturation. In the hue correction step, the hue of the image data after edge enhancement is corrected so that the ratio of the hue of the image data after edge enhancement to the hue of the image data before edge enhancement falls within a predetermined ratio. For this reason, it is possible to prevent the input image from changing to an unintended color by the edge enhancement process, and it is possible to sharpen the image while maintaining the hue of the original image. In the saturation correction step, the saturation of the image data after edge enhancement is corrected so that the ratio at which the saturation of the image data after edge enhancement changes from the saturation of the image data before edge enhancement falls within a predetermined ratio. For this reason, it is possible to prevent the occurrence of whiteout (locally white points) and unintended colors due to extreme changes in saturation.
  A program according to still another aspect of the present invention includes a step of extracting a hue from image data in which each pixel value is represented by coordinates in a predetermined color space, and a step of extracting saturation from the image data. A step of enhancing the edge of the image data for each color component, a step of converting the image data in which the edge is emphasized into image data represented by hue, saturation, and brightness, and a hue before edge enhancement. Is a program for executing a hue correction step for correcting the hue after edge enhancement, and a saturation correction step for correcting the saturation after edge enhancement based on the saturation before edge enhancement. The hue correction step compares the hue of the image data after edge enhancement outputted from the image data conversion step with the hue of the image data before edge enhancement outputted from the step of extracting the hue, and the image data after edge enhancement When the rate at which the hue of the image data changes from the hue of the image data before edge enhancement is greater than a predetermined rate, the hue of the image data after edge enhancement is corrected so as to fall within the predetermined rate. The saturation correction step compares the saturation of the edge-enhanced image data output from the image data conversion step with the saturation of the image data before the edge enhancement output from the step of extracting saturation, and performs edge enhancement. When the rate at which the saturation of the subsequent image data changes from the saturation of the image data before edge enhancement is greater than a predetermined rate, the saturation of the image data after edge enhancement is corrected so that it falls within the predetermined rate. .
  Edge enhancement is performed on each color component of the input image data. For this reason, not only the brightness but also the color Sharpening can be performed even for image data having a constant degree. In the hue correction step, the hue of the image data after edge enhancement is corrected so that the ratio of the hue of the image data after edge enhancement to the hue of the image data before edge enhancement falls within a predetermined ratio. For this reason, it is possible to prevent the input image from changing to an unintended color by the edge enhancement process, and it is possible to sharpen the image while maintaining the hue of the original image. In the saturation correction step, the saturation of the image data after edge enhancement is corrected so that the ratio at which the saturation of the image data after edge enhancement changes from the saturation of the image data before edge enhancement falls within a predetermined ratio. For this reason, it is possible to prevent the occurrence of whiteout (locally white points) and unintended colors due to extreme changes in saturation.
[0068]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0069]
【The invention's effect】
Even an input image having no change in brightness can be sharpened well without changing the hue of the input image. In addition, even an input image in which not only lightness but also saturation does not change can be sharpened well without changing the hue of the input image.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an image processing apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a functional configuration of the image processing apparatus according to the first embodiment of the present invention.
FIG. 3 is a flowchart of processing executed by the image processing apparatus according to the first embodiment of the present invention.
FIG. 4 is a diagram showing an RGB space.
FIG. 5 is a diagram for explaining an HSI 6 pyramid color model;
FIG. 6 is a diagram for explaining H (hue) and S (saturation) using an HSI 6 pyramid color model.
FIG. 7 is a diagram illustrating coefficients of an edge enhancement filter.
FIG. 8 is a flowchart of saturation correction processing.
FIG. 9 is a flowchart of a first modification of saturation correction processing.
FIG. 10 is a flowchart of a second modification of the saturation correction process.
FIG. 11 is a block diagram showing a functional configuration of an image processing apparatus according to a second embodiment of the present invention.
FIG. 12 is a flowchart of processing executed by the image processing apparatus according to the second embodiment of the present invention.
FIG. 13 is a flowchart of hue correction processing.
[Explanation of symbols]
1 computer main body, 2 graphic display device, 3 FD drive, 4 FD, 5 keyboard, 6 mouse, 7 CD-ROM device, 8 CD-ROM, 9 network communication device, 10 CPU, 11 ROM, 12 RAM, 13 hard disk, 20 HSI conversion unit, 21 edge enhancement unit, 22 saturation correction unit, 23 HSI inverse conversion unit, 30 HS extraction unit, 31 edge enhancement unit, 32 HSI conversion unit, 33 hue correction unit, 34 saturation correction unit, 35 HSI Inverse conversion unit.

Claims (7)

An image processing apparatus for sharpening a color image,
Image data is represented by hue, saturation and brightness,
Saturation edge enhancement means for enhancing the saturation edge of the image data;
Brightness edge enhancement means for enhancing the brightness edge of the image data;
A saturation correction unit for correcting the saturation output from the saturation edge enhancement unit based on the saturation of the image data before edge enhancement, connected to the saturation edge enhancement unit;
The saturation correction unit compares the saturation of the image data after edge enhancement by the saturation edge enhancement unit with the saturation of the image data before edge enhancement, and the saturation of the image data after edge enhancement is An image processing apparatus that corrects the saturation of image data after edge enhancement so that the ratio changes from the saturation of image data before edge enhancement is larger than a predetermined ratio. The image processing device further includes first conversion means for converting image data in which each pixel is represented by coordinates in a predetermined color space into image data represented by hue, saturation, and brightness,
The saturation edge enhancement means includes means for enhancing the saturation edge of image data connected to the first conversion means and output from the first conversion means,
Before SL brightness edge enhancement means includes means for connected to said first converting means, emphasizing the brightness of the edge of the image data output from said first converting means,
The saturation correction unit is connected to the first conversion unit and the saturation edge enhancement unit, and is based on the saturation of the image data before edge enhancement output from the first conversion unit. The image processing apparatus according to claim 1, comprising means for correcting the saturation of the image data after edge enhancement output from the edge enhancement means.   Furthermore, the hue output from the first conversion unit, the saturation output from the saturation correction unit, and the lightness are connected to the first conversion unit, the saturation correction unit, and the brightness edge enhancement unit. The image processing apparatus according to claim 2, further comprising: a second conversion unit configured to convert image data represented by brightness output from the edge enhancement unit into coordinates in a predetermined color space.   The saturation correction means determines that the saturation of the image data after edge enhancement output from the saturation edge enhancement means is only when the saturation of the image data before edge enhancement is smaller than a predetermined value. The image processing apparatus according to claim 1, wherein the image processing apparatus permits to be smaller than a saturation of the image data before the edge enhancement. Hue, the color space represented by the saturation and lightness is represented by hexagonal pyramid color model, image processing apparatus according to any one of claims 1-4. Emphasizing the saturation edge of the image data;
Enhancing the lightness edge of the image data;
A computer-readable recording medium storing an image processing program for causing a computer to execute a saturation correction step of correcting the saturation of the image data after edge enhancement based on the saturation of the image data before edge enhancement There,
The saturation correction step compares the saturation of the image data after edge enhancement by the step of enhancing the edge of saturation and the saturation of the image data before edge enhancement, and compares the saturation of the image data after edge enhancement. A computer that corrects the saturation of the image data after edge enhancement so that the degree of change is greater than a predetermined ratio when the degree of change from the saturation of the image data before edge enhancement is larger than a predetermined ratio A computer-readable recording medium on which an image processing program to be executed is recorded. On the computer,
Emphasizing the saturation edge of the image data;
Enhancing the lightness edge of the image data;
A saturation correction step for correcting the saturation of the image data after edge enhancement based on the saturation of the image data before edge enhancement,
The saturation correction step compares the saturation of the image data after edge enhancement by the step of enhancing the edge of saturation and the saturation of the image data before edge enhancement, and compares the saturation of the image data after edge enhancement. A computer that corrects the saturation of the image data after edge enhancement so that the degree of change is greater than a predetermined ratio when the degree of change from the saturation of the image data before edge enhancement is larger than a predetermined ratio A program to make it run.

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