JP3565551B2 - Image binarization device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image binarizing apparatus used for an image pickup device such as a digital camera and for performing binarization processing on an image composed of pixels in a matrix of m rows × n columns.
[0002]
[Prior art]
2. Description of the Related Art A digital camera or the like as an imaging device is provided with a special function called a title function that allows a desired title to be superimposed on a captured image. This means that the prepared title image is separately imaged, and this title image is binarized by an image binarizing device to extract only the title characters and title image portions, and the extracted title characters and title images are extracted. Is superimposed on the image to be superimposed.
[0003]
Then, the binarization processing by such an image binarization device is such that, for an image composed of pixels in a matrix of m rows × n columns, the brightness of each pixel is determined based on a constant binarization level. It is generally performed by comparing and judging whether it is high or low.
[0004]
[Problems to be solved by the invention]
However, when capturing a title image, a so-called halation occurs depending on how light hits, and in the obtained title image, portions having different brightness may occur even with the same background color. In the above-described conventional image binarization apparatus, since the binarization level is fixed, it is determined that the part is a title character or a part of the title image although it is not a title character or a title image, There is a possibility that inconvenience may occur in which a title character or a title image different from the title thought by the user is superimposed.
[0005]
To solve this, it is conceivable to set a plurality of binarization levels and appropriately select the binarization level according to the degree of light hit. However, there is a problem that the processing becomes extremely complicated.
[0006]
By the way, regarding binarization of an image, for example, there are devices described in JP-A-62-133587 and JP-A-8-46860. In the former publication, an image of only a background and an image obtained by adding an object to the image are acquired, and a threshold value for binarization is determined from the luminance and correction coefficient of one pixel obtained from the image of only the background. Thus, only the target object is to be extracted. In this case, however, two images, an image including only the background and an image obtained by adding the target object to the background image, are required, and there is a problem that it takes time and effort to capture the image. .
[0007]
On the other hand, in the case of the latter publication, one taken optical image is divided into a plurality of images having different luminance levels, an appropriate exposure is calculated for each of the divided areas, and an image of each area is divided into an appropriate exposure amount. In this case, a plurality of subjects having a large difference in luminance can be photographed under appropriate exposure conditions. However, in this case, complicated processing such as dividing one image is required. There is.
[0008]
A problem to be solved by the present invention is to enable accurate binarization of an image whose brightness is partially different depending on how light hits.
[0009]
[Means for Solving the Problems]
According to an embodiment of the present invention, there is provided an image binarizing apparatus for binarizing an image formed of m rows × n columns of pixels in a matrix. And a determination unit for sequentially determining whether the luminance of the pixels in the to the n-th column changes by a predetermined amount or more than the previous pixel, and sequentially setting the pixels in the first to n-th columns as reference pixels and determining When the next pixel of the reference pixel is determined to change by a predetermined amount or more, if the change is a change in the decreasing direction, the next pixel is set to black, and the change is changed in the increasing direction. In the case of, the processing unit sets the same color as that of the reference pixel when it is determined that the next pixel does not change by a predetermined amount or more by setting the next pixel to white and then the next pixel of the reference pixel does not change by a predetermined amount. And
[0010]
With such a configuration, it is sequentially determined whether or not the luminance of the pixels in the first to n-th columns of each row changes by a predetermined amount or more than the previous pixel, and the pixels in the first to n-th columns are determined. Are sequentially set as reference pixels, and when the next pixel of the reference pixel changes in a decreasing direction by a predetermined amount or more, the next pixel is set to black. And when it is determined that the pixel next to the reference pixel does not change by a predetermined amount or more, binarization can be performed by setting the same color as that of the reference pixel .
[0011]
For this reason, even if the brightness of an image is partially different depending on how light hits, when the image is binarized at a certain level as in the related art, for example, even if the image is not a title character or a title image, the portion is not the title. It can be prevented from being determined as a part of a character or a title image, and it is possible to binarize with high accuracy without setting a plurality of binarization levels.
[0012]
Further, according to the present invention , prior to the binarization processing of the image, as a result of the determination of all pixels by the determination unit, the pixel should be binarized depending on whether or not there is a pixel whose luminance changes by the predetermined amount or more. A determination unit for determining whether the image is an image, and when the determination unit determines that the image is an image to be subjected to the binarization process, the determination unit repeats the determination for all pixels to perform the binarization by the processing unit. Processing is performed.
[0013]
In this case, when the determination unit determines that the image is not the one to be subjected to the binarization processing only on the background, the image is not subjected to the binarization processing, and the image is determined to be the one to be subjected to the binarization processing. In such a case, since the image is binarized by the processing unit, unnecessary processing need not be performed.
[0014]
In addition, according to the present invention, prior to the image binarization processing, when the change in the first pixel in which the luminance is determined to change by the predetermined amount or more by the determination unit is a change in a decreasing direction, the state at the beginning of the line is changed. White, when a change in the increasing direction, a setting unit that sets the state of the head of the line to black, the processing unit, based on the state of each line set by the setting unit, the setting unit determines the The binarization processing is characterized in that the reference pixel and its luminance change to change from white to black, or from black to white, or to make the same state as the color of the immediately preceding pixel .
[0015]
In this way, based on the white or black state of the first pixel of each row set by the setting unit, it is possible to binarize the change in luminance of each pixel in that row, and the brightness may be partially changed depending on how light hits. Even if the images are different from each other, it is possible to prevent that the part is determined to be a part of the title character or the title image, even though the image is not the title character or the title image, as in the related art. Binary processing can be performed.
[0016]
Further, the present invention is characterized in that the predetermined amount is a change amount of luminance that can distinguish white and black regardless of how light hits. In this case, it is sufficient that an amount of change in luminance that can distinguish white and black is experimentally determined in advance as the predetermined amount regardless of the degree of light hit, thereby enabling accurate binarization processing. Become.
[0017]
Further, the invention is characterized in that the imaging device is a digital camera. This makes it possible to cope with a title function or the like, which is a special function of the digital camera, and allows a title character or a title image desired by the user to be superimposed with high accuracy.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment in which the present invention is applied to a digital camera will be described with reference to FIGS. 1 is a block diagram, FIG. 2 is an operation explanatory diagram, and FIGS. 3 to 5 are operation explanatory flowcharts.
[0019]
As shown in FIG. 1, image data captured by a two-dimensional CCD unit 1 in a matrix of m rows × n columns is digitally converted by an A / D converter 2, and the digitally converted image data is processed by a DSP (Digital). A necessary process such as a pixel interpolation process is performed by a signal processor 3, and then stored in an image memory 5 by a CPU 4.
[0020]
When the title function is selected by operating a key (not shown), for example, the title image separately captured by the CCD unit 1 is used by the CPU 4 for the pixels from the first column to the n-th column of each row. It is sequentially determined whether the luminance changes by a predetermined amount or more than the previous pixel. This determination process corresponds to a determination unit.
[0021]
Note that the predetermined amount at this time is a change amount of luminance that can distinguish white and black irrespective of the degree of light hit, and is desirably experimentally obtained in advance. Is preferable.
[0022]
Further, as a result of the above-described determination for all the pixels of the title image by the CPU 4, whether or not there is a pixel whose luminance changes by a predetermined amount or more is determined as to whether the image is a title image to be binarized. A determination is made as to whether or not. This determination process corresponds to a determination unit.
[0023]
As described above, when it is determined that the title image should be subjected to the binarization processing, when the change in the pixel whose luminance changes by a predetermined amount or more changes in the decreasing direction, the state of the head of the line is white, At the time of change in the increasing direction, the state at the beginning of the line is set to black. This setting process corresponds to a setting unit.
[0024]
Further, based on the white and black states at the head of each line of the title image, the CPU 4 determines whether or not there is a pixel whose luminance changes by a predetermined amount or more for each line. The pixel is subjected to a binarization process assuming that the luminance of the reference pixel changes from white to black if it decreases, and from black to white if it increases. This binarization processing corresponds to a processing unit.
[0025]
Therefore, when the luminance change curve of a certain row is as shown in FIG. 2A, for example, the pixel P1 whose luminance value changes by a predetermined amount or more is detected, and the luminance change in this pixel P1 is in the decreasing direction. Therefore, the state at the head of this row is set to "white", and as shown in FIG. 2B, the area from the beginning of the row to the pixel P1 is maintained at "white", and the pixel P1 is inverted to "black". Is done.
[0026]
Subsequently, as shown in FIG. 2C, the luminance of the pixels after the pixel P1 includes a section in which the luminance decreases by a predetermined amount or more and a section in which the luminance does not change by a predetermined amount or more. Is continuously set to "black", and the same "black" as that of the previous pixel is continuously set in a section where the value does not change by a predetermined amount or more. Therefore, the pixel is held in "black" in these sections. As shown in FIG. 2D, when a pixel P2 whose luminance value increases by a predetermined value or more is detected, the pixel P2 is inverted to “white”, and as shown in FIG. The luminance of the pixel has a section that increases by a predetermined amount or more and a section that does not change by a predetermined amount or more. In the section that increases by a predetermined amount or more, the pixel value continues to be set to “white” and does not change by a predetermined amount. Since the same “white” as the previous pixel is continuously set in the section, the pixel is kept white in these sections.
[0027]
Next, the operation will be described with reference to the flowcharts of FIGS. First, a description will be given of an image determination processing procedure for determining whether or not a title image should be binarized. As shown in FIG. 3, the brightness of the first pixel in the first row and first column is set to a reference value. (Step S1) It is determined whether or not the luminance of the next pixel is larger than the reference value by a predetermined amount or more (Step S2). If the determination result is YES, the state of the pixel having the reference value is “black” (Step S3), it is determined that the image is an image to be binarized, a normal response is returned (step S4), and the operation ends.
[0028]
On the other hand, if the decision result in the above step S2 is NO, it is decided whether or not the luminance of the pixel is smaller than the reference value by a predetermined amount or more (step S5). The state of the pixel having the reference value is set to "white" (step S6), the image is determined to be an image to be binarized, a normal response is returned (step S7), and the operation ends.
[0029]
If the decision result in the step S5 is NO, it is decided whether or not the pixel is the last pixel in the row (step S8). If the decision result is NO, the process returns to the step S2 and the decision result is YES. If so, it is determined whether the row is the last row (step S9). If the determination result is NO, the row is moved to the first pixel of the next row (step S10), and the brightness of the first pixel is The new reference value is set (step S11), and the process returns to step S2.
[0030]
By the way, if the decision result in the step S9 is YES, it is determined that the image is not an image to be subjected to the binarization processing, an abnormal response is returned (step S12), and the operation is thereafter ended. According to such processing, if a normal response is returned, the title image is an image to be binarized, and if an abnormal response is returned, the title image is not an image to be binarized only with the background, for example. I can understand that.
[0031]
Next, a description will be given of a processing procedure for setting a head state of a line for setting whether the state of the head pixel of each row is white or black. As shown in FIG. 4, the brightness of the head pixel of the row is determined in steps S1 and S11 described above. A reference value different from the reference value is set (step S21), and it is determined whether or not the luminance of the next pixel in the row is larger than the reference value by a predetermined amount or more (step S22). If, the state of the pixel having the reference value is set to "black" (step S23), and after a normal response is returned (step S24), the operation ends.
[0032]
On the other hand, if the decision result in the step S22 is NO, it is decided whether or not the luminance of the pixel is smaller than the reference value by a predetermined amount or more (step S25). If the decision result is YES, the reference value Is set to "white" (step S26), and after a normal response is returned (step S27), the operation ends.
[0033]
If the decision result in the step S25 is NO, it is decided whether or not the pixel is the last pixel in the row (step S28). If the decision result is NO, the process returns to the step S2, and the decision result is YES. Then, it can be determined that there is no pixel whose luminance value changes in the row, so that it is determined whether the luminance value of the first pixel in the row itself is “white” or “black” based on a predetermined threshold value. Is performed, and after the state of the first pixel of the row is determined (step S29), a normal response is returned (step S30), and the operation is thereafter terminated.
[0034]
Next, the procedure of the binarization processing will be described. As shown in FIG. 5, first, the image determination processing (see FIG. 3) for determining whether or not the image should be binarized as described above is performed (step S41). It is determined whether or not there is a response (step S42). If the determination result is YES, the binarization processing is useless, and the operation ends as it is.
[0035]
On the other hand, if the decision result in the step S42 is NO, the luminance of the first pixel in the first row and the first column is set to the reference value (step S43), and the luminance of the next pixel is more than the reference value by a predetermined amount or more. It is determined whether or not it is larger (step S44), and if this determination is YES, the next pixel is set to "white" (step S45).
[0036]
Further, if the determination result is NO in step S44, the than the reference value is the luminance of the pixel determination is made whether a predetermined amount or more small (step S46), if the determination result is YES, the pixel Is set to "black" (step S47), and after the process of step S45, the process proceeds to step S48 together with the case where the determination result of step S46 is NO.
[0037]
Then, in step S48, the luminance of the pixel currently being processed is newly set to the reference value (step S48), and the process proceeds to step S49. In step S49, the state of the pixel is written in the image memory 5. Here, if the luminance has not changed by a predetermined amount or more so as to invert the pixel, the state of the pixel is written in the same state as the state of the previous pixel (black to black, white to white). Thereafter, it is determined whether or not the pixel is the last pixel in the row (step S50). If this determination is NO, the process returns to step S44. If the determination is YES, the row is last. Is determined (step S51). If the determination result is NO, the above-described line head state setting processing is performed (step S52), and the luminance of the first pixel of the line is newly set to the reference value. After that (step S53), the process returns to step S44, and if the result of the determination in step S51 is YES, the process ends.
[0038]
As described above, when it is determined that the title image is to be binarized, it is determined whether or not the luminance of the pixels in the first to n-th columns of each row changes by a predetermined amount or more than the previous pixel. The state at the beginning of the line is “white” when the change in the pixel that is determined and the luminance is determined to change by a predetermined amount or more is a change in the decreasing direction, and the state at the beginning of the line is “black” when the change is in the increasing direction. Based on the white or black state at the beginning of each set row, based on the pixels determined to have the brightness of each pixel in the row changing by a predetermined amount or more, the reference pixel and the change in the brightness are determined as the reference pixels. Binarization processing is performed assuming that the color changes from “white” to “black” or “black” to “white”.
[0039]
Therefore, according to the above-described embodiment, even if the brightness of an image is partially different depending on how light hits, it is not a title character or a title image as in the case of binarization at a constant level as in the related art. Nevertheless, it is possible to prevent that part from being determined to be a part of a title character or a title picture, and to perform binarization with high accuracy without setting a plurality of binarization levels. Thus, a desired title image can be superimposed.
[0040]
Further, the binarization processing of the image is performed only when it is determined that the image should be subjected to the binarization processing. Therefore, it is determined that the image is not the one to be subjected to the binarization processing only in the background. Sometimes, unnecessary processing is not performed, and the processing efficiency can be improved.
[0041]
In the above-described embodiment, a case has been described in which the state of the first pixel in each row is set to “white” or “black”. However, it is not necessary to perform such a setting, and the first pixel in each row is not set. It is sequentially determined whether or not the luminance of the pixels in the columns from the column to the n-th column changes by a predetermined amount or more than that of the previous pixel. The pixel before the reference pixel may be binarized as white when the change in the decreasing direction, and black before the reference pixel when the change in the increase direction.
[0042]
In the above-described embodiment, it is determined whether or not the title image should be subjected to the binarization process. However, such a determination is not necessarily performed.
[0043]
Further, in the above-described embodiment, the title function of the digital camera has been described as an example. However, the present invention can be applied to a case where image binarization processing other than the title function is required. Needless to say.
[0044]
In the above-described embodiment, the case where the present invention is applied to a digital camera has been described. However, the present invention is not particularly limited to a digital camera, and the present invention may be applied to any imaging device that requires binarization processing. Is possible, and the same effect as the above-described embodiment can be obtained.
[0045]
Furthermore, the present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention.
[0046]
【The invention's effect】
As described above, according to the invention described in claim 1, it is determined whether the brightness of each pixel changes by a predetermined amount or more than the previous pixel, and a pixel whose brightness changes by a predetermined amount or more is set as a reference pixel. When the change is in the decreasing direction, the pixels subsequent to the reference pixel are black, and when the change is in the increasing direction, the pixels subsequent to the reference pixel are white and are binarized. Even if the brightness of the image is partially different, the image can be accurately binarized without changing the threshold level in the binarization, and a highly accurate binarized image can be obtained. . Further, based on the set white or black state at the head of each row, binarization can be performed based on a change in luminance of each pixel in the row, and an image whose brightness is partially different depending on how light hits. However, the binarization processing can be performed with high accuracy without changing the threshold level at the time of binarization.
According to the second aspect of the present invention, only when it is determined that the image should be binarized, the image is binarized by the processing unit. When the binarization processing is not to be performed only on the background, unnecessary processing is not performed, and the processing efficiency can be improved.
[0049]
According to the third aspect of the present invention, as the predetermined amount, it is sufficient to experimentally determine in advance the amount of change in luminance that can distinguish white and black irrespective of how light hits. Accurate binarization processing becomes possible.
[0050]
Further, according to the invention described in claim 4 , it is possible to cope with a title function or the like which is a special function in the digital camera, and it becomes possible to accurately superimpose a title character or a title image desired by the user.
[Brief description of the drawings]
FIG. 1 is a block diagram of one embodiment of the present invention.
FIG. 2 is an operation explanatory diagram of one embodiment of the present invention.
FIG. 3 is a flowchart for explaining the operation of the embodiment of the present invention;
FIG. 4 is a flowchart for explaining the operation of the embodiment of the present invention;
FIG. 5 is a flowchart for explaining the operation of the embodiment of the present invention;
[Explanation of symbols]
1 CCD unit 2 A / D converter 3 DSP
4 CPU (determination unit, processing unit, determination unit, setting unit)
5 Image memory

Claims (4)

In an image binarization device used for an imaging device, which binarizes an image composed of m rows × n columns of pixels in a matrix,
A determining unit for sequentially determining whether the luminance of a pixel in a first column to an n-th column in each row changes by a predetermined amount or more than that of a previous pixel;
The pixels in the first to n-th columns are sequentially set as reference pixels, and when the determination unit determines that a pixel next to the reference pixel changes by a predetermined amount or more, the change is reduced in a decreasing direction. When the change occurs, the next pixel is set to black, and when the change is an increase, the next pixel is set to white, and it is determined that the next pixel of the reference pixel does not change by a predetermined amount or more. A processing unit that binarizes by setting the same as the color of the reference pixel ,
Prior to the binarization processing of the image, when the change in the first pixel in which the luminance is determined to change by the predetermined amount or more by the determination unit is a change in the decreasing direction, the state at the beginning of the line is white, and the state in the increasing direction is A setting unit that sets the state at the beginning of the line to black when it changes,
The processing unit, based on the state of each line head set by the setting unit, from white to black, or from black to white due to a change in the luminance and the reference pixel determined by the determination unit, or immediately before An image binarization device, wherein a binarization process is performed to set the same state as the color of a pixel. Prior to the binarization processing of the image, as a result of the determination for all the pixels by the determination unit, whether or not the pixel is an image to be subjected to the binarization processing is determined based on whether or not there is a pixel whose luminance changes by the predetermined amount or more Further comprising a determination unit for determining
When the determination unit determines that the image is an image to be subjected to the binarization process, the determination unit repeats the determination for all pixels, and performs the binarization process by the processing unit. 2. The image binarization device according to 1. Wherein the predetermined amount, the image binarization apparatus according to any one of claims 1 to 2, characterized in that a variation in luminance enough to distinguish between white and black regardless degree of lighting. The imaging device, an image binarization system according to any one of claims 1, characterized in that a digital camera 3.

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