JP4089178B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image processing apparatus, an image processing method, and a program for performing background adjustment.
[0002]
  In this specification, “background adjustment” is a concept that includes other background processing in addition to performing background removal processing. “Background removal processing” means that the brightness (gradation value) of each pixel data of the background area (or the area where the paper background appears if the image is printed on paper) is the maximum corresponding to white. Refers to conversion to a value.
[0003]
[Prior art]
  In general, an image processing apparatus detects a background area from input image data, and performs background adjustment such as background removal on the detected background area in order to express an image of a non-background area more clearly. Things have been done.
[0004]
  The background region shows the tendency that the appearance frequency of a specific lightness (gradation) level is the highest. Therefore, as background removal processing conventionally performed by an image processing apparatus, input as shown in FIG. A histogram of the brightness (gradation value) represented by each pixel data in the image is created, the gradation level m having the highest brightness level is obtained, and an area having a brightness higher than the gradation level m (this is referred to as “background” 9), it is known that the brightness data L is converted to a maximum value (255) corresponding to white as shown in FIG. 9B (for example, Japanese Patent Laid-Open No. 2000-83166). Alternatively, as shown in FIG. 9C, the lightness L is converted to the maximum value (255) in the background area, and the area below the gradation level m (this is referred to as a “non-background area”). It is known that linear conversion is performed with a gradient α2 larger than the gradient α1 (= 1) when the background removal process is not performed so that the converted lightness L ′ is continuous.
[0005]
[Problems to be solved by the invention]
  However, since a certain brightness (gradation) level is set and the background area is detected based on this, pixels of the brightness (gradation) level set in the image data in the non-background area are detected. Even if there was, there was a base adjustment using this as a base region.
[0006]
  For example, as shown in FIG. 10A, the input image may have a gradation that smoothly changes in gradation. 10A shows the image as a bitmap image, and FIG. 10A shows the density profile along the center line C of the image (the same applies to FIGS. 10B and 10C). .) In this example, the input image has a gradation that gradually becomes darker from the center to the periphery. When the background removal process as shown in FIGS. 9B and 9C is performed on this input image, the center of the image becomes flat white as shown in FIGS. 10B and 10C, respectively. There is a problem that gradation is lost. For example, like the child's photographic image shown in FIG. 11, the skin of the child who originally has gradation is whitened (the white area is indicated by I). As a result, the smooth gradation of the photographic image has been impaired.
[0007]
  SUMMARY OF THE INVENTION An object of the present invention is to provide an image processing apparatus, an image processing method, and a program for executing the image processing method that can prevent white spots from occurring in a gradation area while performing background adjustment. .
[0008]
[Means for Solving the Problems]
  In order to solve the above problem, an image processing apparatus according to claim 1 is provided.,
  Input means for inputting image data;,
  Reference level calculation means for calculating a reference level for separating the background area and the non-background area from the input image data input by the input means;,
  Ground pixel detection means for detecting pixels included in the ground area in the input image data based on the reference level calculated by the reference level calculation means;,
  Background adjustment means for performing background adjustment on the pixels included in the background area;,
  Included in the base areaBased on the first pixel,At least in one directionOf the second pixelGradation change amount calculating means for calculating the gradation change amount;,
  Based on the gradation change amount calculated by the gradation change amount calculation means,Whether or not there is a gradation around the first pixel included in the background area as a gradation change situationGradation change status identifying means for identifying,
  Based on the gradation change situation identified by the gradation change situation identification means,When gradation exists around the first pixel, the background adjustment unit prohibits the background adjustment for the first pixel, while gradation does not exist around the first pixel.the aboveFirstControl means for performing background adjustment on the pixel by the background adjustment meansWhen
It is provided with.
[0009]
  As described above, a specific example of “background adjustment” is to perform background removal processing.
[0010]
  In the image processing apparatus according to the first aspect, first, image data is input by the input means. Next, the reference level calculation means calculates a reference level for separating the background area and the non-background area from the input image data input by the input means. Based on the reference level calculated by the reference level calculation means, the background pixel detection means detects pixels included in the background area in the input image data. Here, the gradation change amount calculation means is included in the background area.Based on the first pixel,At least in one directionOf the second pixelThe gradation change amount is calculated. Based on the gradation change amount calculated by the gradation change amount calculating means, the gradation change status identifying means isWhether or not gradation exists in the vicinity of the first pixel included in the background area as a gradation change situationIdentify. And the control means,Based on the gradation change situation identified by the gradation change situation identification means,When gradation exists around the first pixel, the background adjustment unit prohibits the background adjustment for the first pixel, while gradation does not exist around the first pixel.the aboveFirstThe background adjustment is performed on the pixel by the background adjustment means.
[0011]
  Thus, in this image processing apparatus,When gradation exists around the first pixel included in the background area, the background adjustment unit prohibits the background adjustment for the first pixel, while gradation does not exist around the first pixel. Whenthe aboveFirstBackground adjustment is performed on the pixel by the background adjustment means. For example, when the background adjustment is a background removal process,It is possible to prevent white spots from occurring in the gradation area and maintain the gradation of the gradation area.
[0012]
  In this specification, the “gradation area” means an area where the brightness and hue of a plurality of pixels are gradually changing in one direction or a plurality of directions.
[0013]
  The image processing device according to claim 2 is the image processing device according to claim 1, wherein the gradation change amount calculation means is included in the ground region.FirstPixelStandardAs multiple directions2nd pixel lined up inIt is characterized in that the gradation change amount is calculated.
[0014]
  In the image processing apparatus according to claim 2, the gradation change amount calculating unit includes the ground area included in the ground region.FirstPixelStandardAs multiple directions2nd pixel lined up inIs calculated by the gradation change status identifying means.FirstAround the pixelWhether there is a gradient in theAccurately identifyit can.
[0015]
  Claim3The image processing apparatus according to claim 1.Or 2In the image processing apparatus described in,
  The above contained in the ground areaFirstA hue extraction means for extracting the hue of a pixel;,
  the aboveFirstPixel hue and aboveFirstThe pixels are arranged in the direction in which the gradation change amount is calculated by the gradation change amount calculation means.SecondBetween pixel hueWhether there is a correlationAnd a hue discrimination means for identifying,
  The control means is based on the identification result by the hue discrimination means,When there is a correlation between the hue of the first pixel and the hue of the second pixel, the background adjustment unit prohibits the background adjustment for the first pixel, while the hue of the first pixel When there is no correlation with the hue of the second pixel,the aboveFirstThe background adjustment is performed on the pixel by the background adjustment means.
[0016]
  This claim3In the image processing apparatus, the hue extracting means includes the above-described background region.FirstExtract the hue of the pixel. The hue discrimination means is the aboveFirstPixel hue and aboveFirstThe pixels are arranged in the direction in which the gradation change amount is calculated by the gradation change amount calculation means.SecondBetween pixel hueWhether there is a correlationIdentify. And the said control means is based on the identification result by the said hue discrimination means,When there is a correlation between the hue of the first pixel and the hue of the second pixel, the background adjustment unit prohibits the background adjustment for the first pixel, while the hue of the first pixel When there is no correlation with the hue of the second pixel,the aboveFirstThe background adjustment is performed on the pixel by the background adjustment means. Therefore, for example, when the background adjustment is a background removal process, the aboveFirstOnly if the pixel is in a gradation area with the same hue and gradually changing brightnessFirstIt is possible to prohibit the background adjustment unit from performing background removal processing for pixels. As a result, the accuracy of acceptance / rejection of the background removal process is increased near the boundary where the regions having different hues are in contact with each other. Therefore, when the gradation area that should not be subjected to the background removal process is in contact with the area that should be subjected to the background removal process, the boundary between the areas can be clearly reproduced after the background adjustment.
[0017]
  The image processing device according to claim 4 is the image processing device according to claim 3,
  The hue determination unit matches the hue of the first pixel with the hue of the second pixel arranged in the direction in which the gradation change amount is calculated by the gradation change amount calculation unit with respect to the first pixel. When identifying that there is a correlation between the hue of the first pixel and the hue of the second pixel, and when the hue of the first pixel and the hue of the second pixel do not match, It is characterized in that there is no correlation between the hue of the first pixel and the hue of the second pixel.
[0018]
  In the image processing apparatus according to claim 4, whether or not there is a correlation between the hue of the first pixel and the hue of the second pixel depends on whether the hue of the first pixel and the second pixel or not. Is identified according to whether or not the hue of the pixel matches.
[0019]
  The image processing method according to claim 5An image processing method executed by the image processing apparatus,
  Enter image dataInput stepWhen,
  A reference level for dividing the background area and the non-background area is calculated from the input image data input above.Reference level calculation stepWhen,
  Based on the calculated reference level, pixels included in the background area in the input image data are detected.Base pixel detection stepWhen,
  Included in the base areaBased on the first pixel,At least in one directionOf the second pixelCalculate gradation changeTone change calculation stepWhen,
  Based on the calculated gradation change amount,Whether or not there is a gradation around the first pixel included in the background area as a gradation change situationIdentifyGradation change status identification stepWhen,
  Based on the identified tone change situation,When gradation exists around the first pixel, background adjustment is prohibited for the first pixel, while gradation does not exist around the first pixel.the aboveFirstPerform background adjustment for pixelsControl steps to control and
It is provided with.
[0020]
  In the image processing method of claim 5, first, image data is input.(Input step). Next, a reference level for separating the background area and the non-background area is calculated from the input image data input above.(Reference level calculation step). Next, pixels included in the background area in the input image data are detected based on the calculated reference level.(Background pixel detection step). Next, it was included in the ground areaBased on the first pixel,At least in one directionOf the second pixelCalculate gradation change(Tone change calculation step). Next, based on the calculated gradation change amount,Whether or not there is a gradation around the first pixel included in the background area as a gradation change situationIdentify(Gradation change status identification step). And based on the identified gradation change situation,When gradation exists around the first pixel, background adjustment is prohibited for the first pixel, while gradation does not exist around the first pixel.the aboveFirstPerform background adjustment for pixelsControl (control step).
[0021]
  Thus, in this image processing method,When gradation is present around the first pixel, background adjustment is prohibited for the first pixel, while when gradation is not present around the first pixel, background adjustment is performed for the first pixel. Control to do. Therefore,For example, when the background adjustment is a background removal process,It is possible to prevent white spots from occurring in the gradation area and maintain the gradation of the gradation area.
[0022]
  The image processing method according to claim 6 comprises:6. The image processing method according to claim 5, wherein in the gradation change amount calculating step, gradation change amounts of second pixels arranged in a plurality of directions with the first pixel included in the background region as a reference are used. It is characterized by calculating.
[0023]
  In the image processing method of claim 6,The gradation change amount calculating step can accurately identify whether or not there is a gradation around the first pixel.
[0024]
  The image processing method according to claim 7 is the image processing method according to claim 5 or 6,
  After the gradation change situation identification step and before the control step,
  A hue extraction step of extracting the hue of the first pixel included in the background region;
  Whether there is a correlation between the hue of the first pixel and the hue of the second pixel arranged in the direction in which the gradation change amount is calculated in the gradation change calculation step for the first pixel A hue discrimination step for identifying
  In the control step, when there is a correlation between the hue of the first pixel and the hue of the second pixel based on the identification result in the hue determination step, background adjustment is prohibited for the first pixel. On the other hand, when there is no correlation between the hue of the first pixel and the hue of the second pixel, control is performed to perform background adjustment for the first pixel.
[0025]
  In the image processing method according to the seventh aspect, the hue of the first pixel included in the background region is extracted by the hue extraction step. In the hue determination step, between the hue of the first pixel and the hue of the second pixel arranged in the direction in which the gradation change amount is calculated by the gradation change amount calculation step with respect to the first pixel. Identify whether there is a correlation. In the control step, when there is a correlation between the hue of the first pixel and the hue of the second pixel based on the identification result in the hue determination step, the background of the first pixel While the adjustment step prohibits background adjustment, when there is no correlation between the hue of the first pixel and the hue of the second pixel, the background adjustment is performed on the first pixel by the background adjustment step. . Therefore, for example, when the background adjustment is a background removal process, the background adjustment step is performed for the first pixel only when the first pixel is a pixel in a gradation region where the brightness gradually changes with the same hue. The background removal process can be prohibited. As a result, the accuracy of acceptance / rejection of the background removal process increases near the boundary where the regions having different hues are in contact with each other. Therefore, when the gradation area that should not be subjected to the background removal process is in contact with the area that should be subjected to the background removal process, the boundary between the areas can be clearly reproduced after the background adjustment.
[0026]
  The image processing method according to claim 8 is the image processing method according to claim 7,
  In the hue determination step, the hue of the first pixel matches the hue of the second pixel arranged in the direction in which the gradation change amount is calculated in the gradation change amount calculation step with respect to the first pixel. When identifying that there is a correlation between the hue of the first pixel and the hue of the second pixel, and when the hue of the first pixel and the hue of the second pixel do not match, It is characterized in that there is no correlation between the hue of the first pixel and the hue of the second pixel.
[0027]
  In the image processing apparatus according to claim 8, whether or not there is a correlation between the hue of the first pixel and the hue of the second pixel is determined based on whether or not there is a correlation between the hue of the first pixel and the second pixel. Can be identified according to whether or not the hue of the pixel matches.
[0028]
  Claim9The program described inThe image processing method according to claim 5.Is a program for causing a computer to execute.
[0029]
  This claim9According to the program of claim 5,To any one of 8This image processing method can be executed by a computer.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0031]
  FIG. 1 shows a block configuration of an image reading apparatus 300 according to an embodiment to which the present invention is applied.
[0032]
  The image reading apparatus 300 includes an operation panel 100 for a user to receive various settings / inputs, a CPU (Central Processing Unit) 200 that controls the entire apparatus, and a ROM (ROM) that stores a program to be executed by the CPU 200. Read-only memory). The image reading apparatus 300 also includes a CCD sensor 111 as input means for obtaining image data from a document, an A / D conversion unit 310 for performing image processing on the image data, a shading correction unit 320, and scaling / movement. A control unit 330, a Lab conversion unit 340, a background level adjustment unit 350, an inverse Lab conversion unit 360, a LOG correction unit 370A, a color correction processing unit 370B, an area determination unit 390, and an MTF correction processing unit 380 are provided.
[0033]
  The document surface is irradiated by an exposure lamp (not shown), and reflected light from the document surface is guided by the optical system and enters the CCD sensor 111. An analog signal obtained by photoelectric conversion of the CCD sensor 111 is converted into multi-value digital image data of R (red), G (green), and B (blue) by an A / D converter 310. The RGB image data is corrected by the shading correction unit 320 so as to eliminate reading variations caused by density unevenness between pixels in the CCD sensor 111 and light distribution unevenness of the exposure lamp. 330 is output.
[0034]
  The input RGB image data is subjected to processing for changing to a magnification previously designated by the operator or moving the position of the image in the scaling / movement control unit 330, and then performing Lab conversion. Is output to the unit 340.
[0035]
  The RGB image data output from the scaling / movement control unit 330 is converted into a color system in L (lightness data) and a and b (chromaticity data) by the Lab conversion unit 340. Lab image data obtained by this conversion is output to the background level adjustment unit 350. The lightness data L is expressed by 256 (0 to 255) gradations.
[0036]
  The background level adjustment unit 350 performs background adjustment on the input Lab image data to prevent document show-through and background fogging.
[0037]
  The Lab image data after the background adjustment is converted again to RGB image data by the inverse Lab conversion unit 360 and output to the LOG correction unit 370A and the color correction processing unit 370B.
[0038]
  The LOG correction unit 370A converts the input RGB data, which is luminance data, into Y (yellow), M (magenta), and C (cyan) density data corresponding to the toner color. On the other hand, the color correction processing unit 370B generates K (black) density data from the YMC density data by UCR (under color removal) processing and inking (BP) processing. The density data is expressed in 256 (0 to 255) gradations.
[0039]
  The CMYK image data, which is density data, is subjected to edge processing by the MTF correction processing unit 380 and then output to a printer (not shown).
[0040]
  On the other hand, the RGB image data output from the inverse Lab conversion unit 360 is also input to the region determination unit 390. The area determination unit 390 determines whether or not the corresponding pixel is an edge part based on the input RGB image data.
[0041]
  FIG. 2 shows a block configuration of the background level adjustment unit 350. The background level adjustment unit 350 includes a reference level calculation unit 351, a jump pixel detection unit 352, a gradation change amount calculation unit 353, and a gradation detection unit that perform predetermined processing on the lightness data L of the input Lab image data. Of the input Lab image data.Hue data a, bAre provided with a hue calculation unit 355 and a hue determination unit 356 for executing predetermined processing. In addition, the background level adjustment unit 350 includes a background adjustment control unit 357 as a control unit, and a background adjustment unit 358 that performs background adjustment according to a background processing control signal from the background adjustment control unit 357.
[0042]
  The reference level calculation unit 351 creates a histogram of lightness (tone value) L from the input Lab image data, and obtains the gray level m having the highest frequency of lightness L. Then, the level m is output to the skipped pixel detection unit 352 as a reference level for separating the background area and the non-background area.
[0043]
  The skip pixel detection unit 352 functions as a background pixel detection unit and detects pixels included in the background region in the input Lab image data based on the reference level m. Specifically, for each pixel in the input Lab image data, the lightness data L of the pixel is compared with the reference level m, and if the lightness L of the pixel is higher than the reference level m, the pixel is It is determined that the pixel is included in the base region (this is referred to as “flight pixel” as appropriate). On the other hand, if the brightness L of the pixel is lower than the reference level m, it is determined that the pixel is a pixel included in the non-background region. The jump pixel detection unit 352 outputs a jump pixel determination signal representing the determination result to the background adjustment control unit 357 for each pixel in the input Lab image data.
[0044]
  As shown in FIG. 3, the gradation change amount calculation unit 353 calculates, for each skipped pixel P, gradation change amounts SL1, SL2,..., SLn in a plurality of directions radially about the skipped pixel P. The gradation change amount forms a window composed of k vertical pixels × k horizontal pixels (k is a natural number of 3 or more) around the skipped pixel P to be processed, and a gradient or Laplacian derivative. Calculated using a filter. As a result, the gradation change amount is obtained by the number of calculated directions (n = 8 in this example) with the skipped pixel P as the center. Note that FIG. 4 shows (a) step, (b) line, (c) shaded type cross section called roof, data obtained through the corresponding gradient filter, and data obtained through the Laplacian filter, respectively. Shown in correspondence.
[0045]
  The gradation detection unit 354 shown in FIG. 2 functions as a gradation change state identification unit, and the jump pixel P is based on the gradation change amounts SL1, SL2,..., SLn calculated by the gradation change amount calculation unit 353. The gradation change situation around is identified. Specifically, the gradation change amounts SL1, SL2,..., SLn are respectively compared with two preset reference values REF1, REF2 (where REF1 <REF2). Here, REF1 is a value for distinguishing between flat and gradation, and the reference value REF2 is a value for distinguishing between gradation and edge. If any gradation change amount SLi (i = 1, 2,..., N) is larger than REF1 and smaller than REF2, the skip pixel P is a pixel in the gradation area. It is judged. If the gradation change amount SLi is smaller than REF1, the skip pixel P exists in the flat region with respect to that direction, and if the gradation change amount SLi is greater than REF2, the skip pixel P becomes an edge with respect to that direction. It is judged that it exists. Then, the gradation detection unit 354 outputs n gradation detection signals indicating whether or not the skip pixel P is a pixel in the gradation region to the background adjustment control unit 357.
[0046]
  The hue calculation unit 355 functions as a hue extraction unit, and calculates the hue of the skip pixel P itself based on the hue data a and b in the input Lab image data. As shown in FIG. 5, the hue of the skipped pixel P itself is represented by arctan (b / a) on the ab plane. In addition, the hue calculation unit 355 calculates the hues of the pixels arranged in each direction in which the gradation change amounts SL1, SL2,..., SLn are calculated by the gradation change amount calculation unit 353 for the skipped pixel P. The hue of pixels arranged in a certain direction is represented, for example, by calculating a hue histogram of pixels arranged in that direction and adopting the most frequently used hue. Alternatively, the hue of pixels arranged in a certain direction is represented by adopting the average value of the hues of pixels arranged in that direction. The hue calculation unit 355 outputs hue information representing a total of (n + 1) hues of the hue of the skipped pixel P itself and the hues of the pixels arranged in the n direction to the hue determination unit 356.
[0047]
  In an image or the like by screen printing, a single pixel has primary color data, and the hue is determined by the area ratio of each primary color. In this case, since the hue of an image occupying a certain area is not known only from the hue of a single pixel, the hue of the jump pixel P is calculated from the hues of a plurality of pixels existing around the jump pixel P.
[0048]
  Based on the hue information from the hue calculation unit 355, the hue determination unit 356 correlates between the hue of the skipped pixel P and the hue of the pixels arranged in the n direction, in this example, the hue of the skipped pixel P and the n direction. It is identified whether or not the hues of the pixels lined up in line match. Then, the hue determination unit 356 outputs n hue determination signals representing these identification results to the background adjustment control unit 357.
[0049]
  The background adjustment control unit 357 sends the background adjustment unit 358 to the background adjustment unit 358 based on the jump pixel determination signal from the jump pixel detection unit 352, the gradation detection signal from the gradation detection unit 354, and the hue determination unit 356. A background processing control signal indicating whether background adjustment should be performed or prohibited is created.
[0050]
  For example, if the skipped pixel P is a pixel in the gradation area where the brightness gradually changes with the same hue, the background adjustment unit 358 is prohibited from performing background skip processing for the skipped pixel P, while the skipped pixel P is otherwise If the pixel is included in this area, a background processing control signal indicating that the background adjustment unit 358 performs background removal processing for the skipped pixel P is generated.
[0051]
  The background adjustment unit 358 performs background removal processing unless receiving a background processing control signal (non-active) indicating that background removal processing is prohibited from the background adjustment control unit 357. In this example, the background removal process performed by the background adjustment unit 358 creates a histogram of lightness (tone value) represented by each pixel data in the input image as shown in FIG. 9 is obtained, and in an area where the brightness is higher than the reference level m (this is regarded as a “background area”), the brightness data L corresponds to white as shown in FIG. It shall be converted to the maximum value (255).
[0052]
  FIG. 6 shows an overall control flow of the background level adjustment unit 350. Hereinafter, the operation of the background level adjustment unit 350 will be described with reference to the flow of FIG. 6 and the image data (represented by a bitmap image) and the brightness profile illustrated in FIGS. 7A and 7B. In FIGS. 7A and 7B, the upper row represents image data, and the lower row represents the brightness profile of each corresponding image data.
[0053]
  The upper part of FIG. 7A illustrates input image data (original image). This input image data includes a background area 1 as a background and a gradation area 3 having a conical brightness profile as a non-background area. As shown in the lower part of FIG. 7A, the brightness data is L = m1 (≈200) in the background area 1, L = 255 (white) in the center in the gradation area 3, and L≈100 in the edge. Yes.
[0054]
  First, the reference level m is obtained by the reference level calculation unit 351 (S1 in FIG. 6). In the example of FIG. 7A, the reference level m is slightly lower than m1.
[0055]
  Next, the skip pixel detection unit 352 detects a pixel (a skip pixel) included in the background region 1 in the input Lab image data (S2 in FIG. 6).
[0056]
  Next, a gradation change amount calculation unit 353 processes a certain skipped pixel, and calculates gradation change amounts SL1, SL2,..., SLn in a plurality of directions radially around the skipped pixel (processing target skipped pixel). Calculate (S3).
[0057]
  Next, the gradation detecting unit 354 compares the gradation change amounts SL1, SL2,..., SLn with two preset reference values REF1, REF2 (where REF1 <REF2) (S4). . As described above, REF1 is a value for distinguishing between flat and gradation, and the reference value REF2 is a value for distinguishing between gradation and edge. Here, if any gradation change amount SLi is smaller than REF1 or any gradation change amount SLi is larger than REF2 for the processing target skip pixel, the processing target skip pixel is outside the gradation region. The pixel is determined to be a pixel (NO in S4), and the subsequent processing is passed.
[0058]
  On the other hand, if any gradation change amount SLi (i = 1, 2,..., N) is larger than REF1 and smaller than REF2 for the processing target skipped pixel, the processing target skipped pixel is in the gradation area. (S4: YES). In this case, the hue calculation unit 355 calculates the hues of the pixels arranged in each direction in which the gradation change amounts SL1, SL2,..., SLn are calculated by the gradation change amount calculation unit 353 with respect to the processing target skipped pixels. (S5). Further, the hue calculation unit 355 calculates the hue of the processing target skipped pixel itself based on the hue data a and b in the input image data (S6).
[0059]
  Next, based on the hue information from the hue calculation unit 355, the hue determination unit 356 determines whether the hue of the skip target pixel matches the hue of the pixels arranged in one of the n directions. Is identified (S7). Here, if the hue of the skip target pixel does not match the hue of the pixels arranged in the n direction (NO in S7), the subsequent processing is passed.
[0060]
  On the other hand, if the hue of the processing target skipped pixel matches the hue of the pixel aligned in any one of the n directions, the pixel in the gradation area where the processing target skipped pixel has the same hue and the brightness gradually changes. (YES in S7). In this case, the background adjustment control unit 357 creates a background processing control signal indicating that the background adjustment unit 358 prohibits (cancels) the background removal processing for the processing target skipped pixel (S8). And the process of step S3-S8 is repeated with respect to all the skip pixels (S9).
[0061]
  Thereafter, the background adjustment unit 358 performs background adjustment in accordance with the background processing control signal from the background adjustment control unit 357. In this example, if the processing target skip pixel is a pixel in the gradation region where the brightness gradually changes with the same hue, the background skip processing is not performed on the processing target skip pixel. On the other hand, if the processing target skip pixel is a pixel included in another region, the background skip processing is performed on the processing target skip pixel.
[0062]
  As a result, as shown in FIG. 7B, the brightness profile of the gradation area 3 is the same as that of the input image data, and image data in which only the brightness of the background area 1 is converted to 255 (white) is obtained. Therefore, white spots can be prevented from occurring in the gradation area 3. Moreover, the accuracy of acceptance / rejection of the background removal process is increased near the boundary where the regions 1 and 3 having different hues contact each other. For example, as shown in FIG. 8, when a gradation image (photo image) A1 that should not be subjected to background removal processing is in contact with a frame image A2 that should be subjected to background removal processing, these images A1 and A2 are in contact with each other. The boundary can be clearly reproduced after the substrate adjustment.
[0063]
  In this embodiment, L, a, and b are used as input image data to be processed by the background level adjustment unit 350. However, as long as lightness and hue information is included, data in other color spaces may be used. good.
[0064]
  In the above embodiment, the background removal process has been described as an example of the background adjustment, but the background adjustment may be a process of coloring the background to a specific color (for example, an intermediate color).
[0065]
【The invention's effect】
  As is clear from the above, according to the image processing apparatus of the present invention, white spots are prevented from occurring in the gradation area, and the gradation of this area can be maintained.
[0066]
  According to the image processing method of the present invention, white spots can be prevented from occurring in the gradation area, and the gradation of this area can be maintained.
[0067]
  Further, according to the program of the present invention, the computer can execute the image processing method of the present invention.
[Brief description of the drawings]
FIG. 1 is a diagram showing a block configuration of an image reading apparatus 300 according to an embodiment to which the invention is applied.
FIG. 2 is a diagram showing a block configuration of a ground level adjustment unit 350;
FIG. 3 is a diagram illustrating a direction in which a gradation change amount is calculated with respect to a skipped pixel P with the skipped pixel P as a center.
FIGS. 4A and 4B correspond to a shade section of a type called “a” step, “b” line, and “c” roof, and data obtained through a corresponding gradient filter and data obtained through a Laplacian filter, respectively. FIG.
FIG. 5 is a diagram illustrating the hue of a skipped pixel P itself on an ab plane.
6 is a diagram illustrating a control flow of a background level adjustment unit 350. FIG.
FIG. 7 is a diagram showing image data and a brightness profile.
FIG. 8 is a diagram illustrating image data in which a gradation image (photo image) A1 that should not be subjected to background removal processing and a frame image A2 that should be subjected to background removal processing are in contact with each other.
FIG. 9 is a diagram for explaining a conventional background removal process.
FIG. 10 is a diagram illustrating a problem caused by a conventional background removal process.
FIG. 11 is a diagram illustrating a bad photographic image after the background removal process.
[Explanation of symbols]
  1 Ground area
  3 Non-ground area
  300 Image reader
  350 Ground level adjuster

Claims (9)

Input means for inputting image data;
Reference level calculation means for calculating a reference level for separating the background area and the non-background area from the input image data input by the input means;
Ground pixel detection means for detecting pixels included in the ground area in the input image data based on the reference level calculated by the reference level calculation means;
Background adjustment means for adjusting the background for the pixels included in the background area;
Gradation change amount calculating means for calculating the gradation change amount of the second pixels arranged in at least one direction with reference to the first pixel included in the base region;
Based on the gradation change amount calculated by the gradation change amount calculating means, it is identified whether or not a gradation exists around the first pixel included in the background area as a gradation change situation. Gradation change status identifying means;
On the basis of the gradation change situation identified by the gradation change situation identification means, when gradation exists around the first pixel, the background adjustment means prohibits the background adjustment for the first pixel. An image processing apparatus comprising: a control unit that causes the background adjustment unit to perform background adjustment on the first pixel when gradation does not exist around the first pixel. The image processing apparatus according to claim 1.
The image processing apparatus according to claim 1, wherein the gradation change amount calculating means calculates a gradation change amount of second pixels arranged in a plurality of directions with the first pixel included in the background region as a reference . The image processing apparatus according to claim 1 or 2 ,
Hue extraction means for extracting the hue of the first pixel included in the background area;
Whether there is a correlation between the color of the first pixel, the hue of the second pixels arranged in the direction of calculation of gradation change amount by the gradation change amount calculating means with respect to the first pixel And a hue discrimination means for identifying
The control means has the background adjustment means for the first pixel when there is a correlation between the hue of the first pixel and the hue of the second pixel based on the identification result by the hue discrimination means. The background adjustment is prohibited, and when there is no correlation between the hue of the first pixel and the hue of the second pixel, the background adjustment unit performs the background adjustment on the first pixel. A featured image processing apparatus. The image processing apparatus according to claim 3.
The hue determination unit matches the hue of the first pixel with the hue of the second pixel arranged in the direction in which the gradation change amount is calculated by the gradation change amount calculation unit with respect to the first pixel. When identifying that there is a correlation between the hue of the first pixel and the hue of the second pixel, and when the hue of the first pixel and the hue of the second pixel do not match, An image processing apparatus that identifies that there is no correlation between the hue of the first pixel and the hue of the second pixel. An image processing method executed by an image processing apparatus,
An input step for inputting image data;
A reference level calculating step for calculating a reference level for separating the background area and the non-background area from the input image data input;
A background pixel detection step for detecting pixels included in the background area in the input image data based on the calculated reference level;
A gradation change amount calculating step for calculating a gradation change amount of the second pixels arranged in at least one direction with reference to the first pixel included in the base region;
A gradation change situation identifying step for identifying whether or not gradation exists around the first pixel included in the background area as a gradation change situation based on the calculated gradation change amount; ,
Based on the identified tone change situation, when the gradient in the periphery of the first pixel exists, while prohibiting base adjustment for the first pixel, gradients around the first pixel An image processing method comprising: a control step of performing background adjustment for the first pixel when it does not exist . The image processing method according to claim 5,
In the gradation change amount calculating step, the gradation change amount of second pixels arranged in a plurality of directions with respect to the first pixel included in the background region is calculated. The image processing method according to claim 5 or 6,
After the gradation change situation identification step and before the control step,
A hue extraction step of extracting the hue of the first pixel included in the background region;
Whether there is a correlation between the hue of the first pixel and the hue of the second pixel arranged in the direction in which the gradation change amount is calculated in the gradation change calculation step for the first pixel A hue discrimination step for identifying
In the control step, when there is a correlation between the hue of the first pixel and the hue of the second pixel based on the identification result in the hue determination step, background adjustment is prohibited for the first pixel. On the other hand, when there is no correlation between the hue of the first pixel and the hue of the second pixel, control is performed to perform background adjustment for the first pixel. The image processing method according to claim 7,
In the hue determination step, the hue of the first pixel matches the hue of the second pixel arranged in the direction in which the gradation change amount is calculated in the gradation change amount calculation step with respect to the first pixel. When identifying that there is a correlation between the hue of the first pixel and the hue of the second pixel, and when the hue of the first pixel and the hue of the second pixel do not match, An image processing method characterized by discriminating that there is no correlation between the hue of the first pixel and the hue of the second pixel. A program for causing a computer to execute the image processing method according to any one of claims 5 to 8 .

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