JP4581445B2 - Image processing apparatus, image processing method, and image processing program - Google Patents

Description

  The present invention relates to an image processing apparatus that performs image processing using a gradation value histogram or the like.

  There is known a method of creating a frequency distribution (histogram) of gradation values of image data and processing the image data based on the frequency distribution. For example, in Patent Document 1, a histogram of gradation values of image data is created, and a minimum gradation value and a maximum gradation value (hereinafter, these gradation values are defined as “ An image processing method is described in which a specific gradation value is called and the dynamic range of the gradation value is expanded using the specific gradation value. In addition, Patent Document 2 and Patent Document 3 also describe an image processing method using a histogram similar to the above.

  However, since the disclosed technology as described above creates a histogram for each gradation, a large memory size is required when creating the histogram. Furthermore, a histogram is created for each display frame. For example, when a moving image with a video source of 30 fps is displayed at 60 fps, the histogram is the same image (in order to use the same image twice to double the frame rate). ) May also be created. For the reasons described above, the disclosed technique as described above has a problem that it is necessary to provide a memory having a relatively large storage capacity for creating a histogram in the image processing apparatus, which increases the memory cost.

JP-A-8-317250 JP 10-198802 A Japanese Patent No. 3456032

  The present invention has been made in view of the above points, and by creating a histogram of gradation values in a plurality of stages for the same frame data, the memory used for histogram creation can be reduced. An object is to provide a possible image processing apparatus.

  In one aspect of the present invention, an image processing apparatus creates a histogram indicating a frequency distribution by grouping a predetermined number of gradations of acquired frame data, and determines an effective gradation range based on the created histogram. Histogram generating means for generating the histogram divided into a plurality of times for the frame data acquired a plurality of times, and only in the effective gradation range determined in the previous histogram creation. Create a histogram for it.

  The processing apparatus includes a histogram creation unit that creates a histogram indicating the frequency distribution of gradation values for the acquired frame data each time frame data is acquired. The histogram creation means creates a histogram by counting the frequency for each predetermined gradation, and determines an effective gradation range from the created histogram. The histogram creating means creates the histogram by dividing the frame data acquired a plurality of times into a plurality of times. At this time, the histogram creation means creates a histogram only for the effective gradation range determined at the time of the previous histogram creation. That is, the histogram creation means creates the histogram in a plurality of stages. Thereby, the image processing apparatus can reduce the memory for creating the histogram.

  In one aspect of the present invention, the image processing apparatus may be configured such that the effective gradation range is a group of a minimum gradation number exceeding a first predetermined value in a histogram created in order from a small gradation value, or a large gradation. A group of the maximum number of gradations exceeding a second predetermined value in a histogram created in order from the value, and the histogram generation means is the group of the minimum number of gradations determined in the previous histogram generation, or A histogram is created only for the group with the maximum number of gradations. In this aspect, the histogram creating means determines an effective gradation range using the first predetermined value or the second predetermined value as a threshold value. Then, the histogram creation means creates a histogram only for the group with the minimum number of gradations or the group with the maximum number of gradations exceeding these thresholds. As a result, the image processing apparatus can accurately determine the gradation value that defines the effective gradation range of the acquired frame data.

  In another aspect of the present invention, in the image processing apparatus, the histogram creating means creates the histogram in n times, and sets the predetermined number of gradations to the nth power of the number of gradations of the acquired frame data. Determine based on roots. As a result, the amount of memory for creating the histogram is reduced in the order of the nth root of the number of gradations of the frame data, compared to the amount of memory required for creating the histogram for each number of gradations.

  In another aspect of the present invention, a storage means for storing frame data to be processed and a reading means for reading out the stored frame data are provided, and the histogram creation means is configured to read the same frame read a plurality of times. The histogram is created by dividing the data into a plurality of times. In this aspect, the histogram creation means reads the frame data stored in the storage means a plurality of times. That is, the histogram creation means reads the same frame data a plurality of times, and creates a histogram by dividing it into a plurality of stages. As a result, the process of creating the same histogram for the same frame data is not repeated, so that the image processing apparatus can reduce the memory for creating the histogram.

  In another aspect of the present invention, in the image processing apparatus, the histogram creation means is less than the number of times the same frame data is read when adjacent frame data stored by the storage means is approximate. The histogram is created by the number of times. When adjacent frame data is approximated, such as when the previous specific gradation value is included in the gradation group obtained in the first histogram creation, the histogram is created only once and the image Process. In such a case, the specific gradation value determined from the previous frame data is close to the specific gradation value of the next frame data to be processed, so a histogram is created multiple times to determine the exact specific gradation value. do not have to. As a result, the processing circuit does not have to create the second histogram, so that power consumption can be reduced. Further, when the above processing is performed by software, the processing time can be shortened.

  According to another aspect of the present invention, in the image processing apparatus, the histogram generating means is less than the number of times the same frame data is read when the storage and reading of the frame data satisfy a predetermined condition. The histogram is created by the number of times. As the predetermined condition, there is a case where writing of frame data is not completely synchronized with the frame synchronization signal. In such a case, the histogram creation means determines an effective gradation range from the histogram created halfway. As a result, even if gradation correction using an effective gradation range determined from the histogram is performed, the image to be displayed thereafter is not greatly disturbed.

  In a preferred embodiment of the image processing apparatus, the histogram creating means creates the histogram in two steps, and the first time, 16 gradations are applied to the read 256 gradation frame data. A histogram is created by grouping the numbers, and the second time a histogram is created by grouping the number of one gradation.

  In another aspect of the present invention, an image processing program is executed on a computer to create a histogram showing a frequency distribution by grouping a predetermined number of gradations of acquired frame data, and the generated histogram is stored in the generated histogram. A histogram generation unit that determines an effective gradation range based on the histogram generation unit, which generates the histogram in a plurality of times for frame data acquired a plurality of times, and is determined in the previous histogram generation. A histogram is created only for the effective gradation range. By executing this image processing program on a computer, it is possible to reduce a memory for creating a histogram, as in the case of the above-described image processing apparatus.

  In still another aspect of the present invention, an image processing method creates a histogram showing a frequency distribution by grouping a predetermined number of gradations of acquired frame data, and determines an effective gradation range based on the created histogram. A histogram creation step for determining, wherein the histogram creation step creates the histogram in a plurality of times for the frame data acquired a plurality of times, and only the effective gradation range determined in the previous histogram creation. Create a histogram for. Also by this image processing method, the above-described image processing apparatus can be realized in the same manner as the above-described image processing apparatus.

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

[Configuration of image display device]
An image display apparatus including an image processing unit according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a schematic configuration of an image display apparatus 20 according to an embodiment of the present invention.

  The image display device 20 includes an image generation unit 1, an image processing unit 2, and an image display unit 3. In the image display device 20, the image generated by the image generation unit 1 is appropriately subjected to image processing by the image processing unit 2, and the image processed image is displayed on the image display unit 3.

  The image generation unit 1 includes a CPU, a RAM, a ROM, a drawing device, a disk drive device, control software, and the like (not shown). The image generation unit 1 supplies a signal S1 corresponding to the generated image to the image processing unit 2. Note that the image display device 20 may be configured to include a receiving device that obtains an image to be processed or displayed from the outside without including the image generation unit 1 that generates an image to be displayed.

  The image processing unit 2 includes a frame memory 11, a histogram creation unit 12, a tone value search unit 13, and a tone correction unit 14. The image processing unit 2 functions as the above-described image processing device. The image processing unit 2 illustrated in FIG. 1 has a configuration including only a processing unit for creating a histogram according to the present embodiment, but the image processing unit 2 can perform other image processing. A processing unit can also be provided.

  The frame memory 11 acquires the signal S1 output from the image generation unit 1 and is written with frame data. The frame data S2 written in the frame memory 11 is read out by the histogram creation unit 12 and the gradation correction unit 14. The frame memory 11 functions as a storage unit that stores the above-described frame data. It should be noted that writing to the frame memory 11 is more effective than reading to prevent the displayed image from being disturbed (ie, “tearing”) by overwriting or overtaking frame data in the frame memory 11. It shall be performed at a fast timing and speed.

  The histogram creation unit 12 reads the frame data S2 stored in the frame memory 11, and creates a histogram (frequency distribution) indicating the relationship between the gradation value and the frequency for the frame data S2. At this time, the histogram creation unit 12 acquires a signal S6 corresponding to the timing related to the histogram creation process from the image generation unit 1, and creates a histogram based on the timing signal S6. Details of the histogram creation processing according to the present embodiment in the histogram creation unit 12 will be described later.

  The gradation value searching unit 13 acquires a signal S3 corresponding to the histogram created by the histogram creating unit 12 described above. The gradation value search unit 13 determines a specific gradation value from the signal S3. Then, the gradation value search unit 13 supplies a signal S4 corresponding to the determined specific gradation value to the gradation correction unit 14. As described above, the histogram creation unit 12 and the gradation value search unit 13 function as the above-described histogram creation unit.

  Here, the specific gradation value will be described with reference to FIG. FIG. 2 shows an example of a histogram of gradation values created by a generally performed method. In this example, it is assumed that the histogram creation unit 12 acquires 256 gradation frame data and performs processing on such data. In FIG. 2, the horizontal axis represents the range of the number of gradations, and the vertical axis represents the frequency of the number of gradations in the range (for example, the number of pixels). In this case, the cumulative frequency is obtained for each gradation. Obtaining the accumulation frequency for each gradation means counting the number of pixels having the gradation value for each gradation value and accumulating it to create a histogram. Therefore, the histogram creation unit 12 needs to obtain a frequency corresponding to 256 gradations at the maximum. Further, FIG. 2 shows a histogram created sequentially from the gradation value 0 on the left side of the paper, and a histogram created sequentially from the gradation value 255 on the right side of the paper. In the following description, “histogram created sequentially from tone value 0” means a cumulative histogram created from tone value 0 in the direction of increasing tone values. Similarly, the “histogram created by ranking from the gradation value 255” means a cumulative histogram created from the gradation value 255 in a direction in which the gradation value decreases.

  The specific gradation value is a maximum gradation value or a minimum gradation value whose frequency exceeds a predetermined value (threshold value) in the histogram created as described above. Specifically, in the histogram created in order from the gradation value 0, the minimum gradation value P1 exceeding the threshold value M1 corresponds to the specific gradation value. In the histogram created in order from the gradation value 255, the maximum gradation value P2 exceeding the threshold value M2 corresponds to the specific gradation value.

  The specific gradation value thus determined by the gradation value search unit 13 is supplied to the gradation correction unit 14. The tone correction unit 14 acquires a signal S4 corresponding to the specific tone value determined by the tone value search unit 13 and frame data S2 stored in the frame memory. Then, the gradation correction unit 14 performs gradation correction on the frame data based on the specific gradation value. As a result, an image that effectively uses the dynamic range of the gradation value is created.

  Specific gradation correction performed by the gradation correction unit 14 will be described with reference to FIG. In FIG. 3, the horizontal axis represents the input gradation, and the vertical axis represents the output gradation after gradation correction. The input gradation and the output gradation have a relationship as indicated by a straight line A1. The straight line A1 is defined using the minimum gradation value P1 and the maximum gradation value P2 determined by the gradation value search unit 13. In the gradation correction using the straight line A1, when the input gradation value is the minimum gradation value P1 or less, it is converted to the gradation value 0, and when the input gradation value is the maximum gradation value P2 or more, the gradation value is 255. Convert. Further, when the input gradation value is larger than the minimum gradation value P1 and smaller than the maximum gradation value P2 (in the range indicated by Q), conversion is performed so as to take a value between gradation values 0 and 255. As described above, the gradation correction unit 14 eliminates gradation values that are less than or equal to the minimum gradation value P1 or greater than or equal to the maximum gradation value P2, and is in a range that is greater than the minimum gradation value P1 and less than the maximum gradation value P2. Correction conversion is performed so that the tone value is expressed finely.

  Returning to FIG. 1, the image display unit 3 will be described. The image display unit 3 includes a display device such as an LCD (Liquid Crystal Display) or an OLED (Organic Light Emitting Diode), and displays the image data S5 processed by the image processing unit 2. Further, the image display unit 3 can further perform image processing on the acquired image data S5.

  FIG. 4 is a time chart showing a specific example of signals and processing flow in the processing unit. In the example shown in FIG. 4, the image display unit 20 is displayed on the image display unit 20 at a rate twice the rate of the video source. For example, the image display unit 20 causes the image display unit 20 to display frame data whose video source is 30 fps at 60 fps. In this case, frame data S1 is transmitted every other frame synchronization signal S10, and the frame data S1 is written into the frame memory 11.

  The frame data S1 written in the frame memory 11 is read out to the histogram creation unit 12 in synchronization with the frame synchronization signal S10. As shown in FIG. 4, the histogram creation unit 12 reads the same frame data twice. For example, although frame # 0 and frame # 1 are written into the frame memory 11 once, the histogram creation unit 12 reads out the data twice. The histogram creation unit 12 creates a histogram in two steps for the same read frame data. In this case, when the frame data is read for the first time, the histogram creation unit 12 creates a histogram in the coarsely set gradation range, and roughly determines a group of gradation values including the specific gradation value. . Then, when the frame data is read for the second time, the histogram creation unit 12 creates a histogram with a fine gradation range only for the group including the specific gradation value determined for the first time. That is, the histogram creation unit 12 determines the specific gradation value by performing the histogram creation process twice. Therefore, the histogram creation unit 12 does not create the same histogram for the read same frame data.

  The signal S3 corresponding to the histogram created for the second time as described above is supplied to the gradation value search unit 13. The gradation value search unit 13 determines a specific gradation value from the acquired histogram created for the second time. The signal S4 corresponding to the determined specific gradation value is supplied to the gradation correction unit 14. Then, the gradation correction unit 14 acquires the frame data S1 stored in the frame memory 11, and performs gradation correction using the specific gradation value. Then, the signal S5 corresponding to the tone-corrected frame data is supplied to the image display unit 3 and displayed.

[Histogram creation method]
Next, a histogram creation method according to the embodiment of the present invention will be described. As described above, the histogram creation method according to the present embodiment is performed when the rate of reading frame data is higher than the rate of writing frame data, that is, when the same frame data is read and displayed a plurality of times. In the following description, a histogram creation method for creating a histogram in two steps will be described as an example.

  FIG. 5 shows a specific example of a histogram created by the histogram creation method according to this embodiment. In this example, it is assumed that the histogram creation unit 12 acquires frame data of 256 gradations and performs processing on it. In FIG. 5, as in FIG. 2 described above, the horizontal axis indicates the range of gradation values, and the vertical axis indicates the frequency (for example, the number of pixels) of the gradation values in the range. In FIG. 5, a histogram created in order from the gradation value 0 is shown on the left side of the page, and a histogram created in order from the gradation value 255 is shown on the right side of the page. Further, FIG. 5A shows a histogram created for the first time, and FIG. 5B shows a histogram created for the second time.

  First, FIG. 5A showing the histogram and the like created for the first time will be described. As shown in FIG. 5A, the histogram creating unit 12 obtains the cumulative frequency of gradation values for every 16 gradations, not for every gradation. For example, the histogram creation unit 12 obtains the frequency of the gradation value for each range of 16 gradations, such as a range of 0 gradations to 15 gradations, a range of 0 gradations to 31 gradations, and so on. Therefore, the histogram creation unit 12 only needs to obtain the frequency for at most 16 groups. Note that the number of 16 gradations when creating a histogram corresponds to the square root of 256 gradations to be input.

  Next, the histogram creating unit 12 uses a histogram created in units of 16 groups for each gradation value from 0 to 16 gradations, and uses the histogram of the smallest gradation value exceeding the threshold M1 (hereinafter referred to as “minimum floor”). And a group of maximum gradation values exceeding the threshold M2 (hereinafter referred to as “maximum gradation group”). In the example shown in FIG. 5A, the minimum gradation group is a group of “64 to 79”, and the maximum gradation group is a group of “160 to 175”. In this way, a group of gradation values including a specific gradation value is determined by the first histogram creation. Note that the gradation value search unit 13 may determine the minimum gradation group and the minimum gradation group at the time of creating the first histogram.

  The second histogram creation will be described with reference to FIG. As shown in FIG. 5B, in the second histogram, the minimum gradation group is for each gradation value of “64 to 79” and the maximum gradation group is for each gradation value of “160 to 175”. Only created. In this case, the histogram creation unit 12 obtains the frequency for each gradation. Therefore, the histogram creation unit 12 obtains the frequency for 16 gradations at the maximum. The tone value search unit 13 determines the minimum tone value exceeding the threshold M1 using the histogram created for the 64 to 79 minimum tone groups created in this way. In this case, the minimum gradation value is 72. In addition, the tone value search unit 13 determines the maximum tone value that exceeds the threshold M2 using the histogram created for the maximum tone groups 160 to 175. In this case, the maximum gradation value is 169. The minimum gradation value and the maximum gradation value determined in this way correspond to the specific gradation value.

  As described above, in the histogram creation method according to the present embodiment, when the same frame data is displayed a plurality of times, a specific gradation value is determined by creating a histogram divided into a plurality of times. Here, the effect of the histogram creation method according to the present embodiment will be described. First, the histogram creation unit 12 needs to secure a memory for holding a frequency value corresponding to one gradation group whose frequency is to be calculated. For this reason, the amount of memory to be secured increases according to the number of gradation groups whose frequencies are to be calculated. For example, when a 6-bit memory is secured for one gradation group for which the frequency is to be calculated, the frequency is calculated for each gradation in a generally performed histogram creation method, so that a maximum of 6 × 256 bits is obtained. Memory will be used. On the other hand, since the frequency is obtained every 16 gradations in the histogram creation method according to the present embodiment, if a 6-bit memory is secured for one gradation group, a maximum 6 × 16-bit memory is used. Will be. Therefore, comparing the histogram creation method according to this embodiment with a general method, it can be seen that the amount of memory is reduced on the order of the square root of 256 gradations. As described above, in the histogram creation method according to the present embodiment, since the histogram is created in a plurality of times, the amount of memory required for creating the histogram may be small. Therefore, the memory cost in the image processing unit 2 can be reduced.

  Note that the histogram creation method according to the present embodiment can cope with a case where writing of frame data is not completely synchronized with the frame synchronization signal S10. Below, the coping method etc. are demonstrated using FIG.

  FIG. 6 shows the histogram creation method and the histogram used for gradation correction, which are classified according to the time when the frame data is written. In FIG. 6, the horizontal axis represents time, the upper row represents the frame synchronization signal S10, the middle area C1 represents the frame data write start position and the write end position, and the lower section C3 represents the frame memory. 11 shows the start position and end position of processing for reading out frame data from 11 and creating a histogram. Note that the processing described below is performed by the histogram creation unit 12 and the gradation value search unit 13 observing the write address and the read address of the frame memory 11. That is, the address is continuously observed from the start to the end of writing and reading.

  FIG. 6A shows a case where the next frame data is written during the second histogram creation process. An arrow B1 indicates a writing start position of the frame data # 1, and an arrow B2 indicates a writing start position of the frame data # 2. From FIG. 6A, it can be seen that the frame data # 2 that should have been originally written from the position indicated by the arrow B22 is written from the position indicated by the arrow B2. In this case, the writing of the frame data # 1 does not pass the second histogram creation process for the frame data # 0. Therefore, tone correction is performed on the frame data # 1 based on the second histogram obtained from the frame data # 0.

  FIG. 6B shows a case where the next frame data is overtaken during the second histogram creation process. From FIG. 6B, it can be seen that the writing of the frame data # 1 starts in the middle of the second histogram creation process for the frame data # 0, and the overtaking occurs at the position of the broken line B3. That is, in the histogram creating unit 12, the frame data read from the frame memory 11 is changed from the frame data # 0 to the frame data # 1 during the second histogram creating process. Therefore, the second histogram created by the histogram creation unit 12 is a mixture of frame data # 0 and frame data # 1.

  In the above case, the histogram created at the second time may be different from the result of the histogram created at the first time. For example, when the minimum gradation group is 64 to 79 in the histogram created at the first time, the frequency value at the gradation value 64 greatly exceeds the threshold in the histogram created at the second time, In some cases, the frequency value at the value 79 does not reach the threshold value. In such a case, the gradation value search unit 13 uses gradation values (for example, 64 or 79) at both ends of the histogram created second time as the specific gradation value. Such processing causes a change in the direction to approach the feature of the next frame data, so there is no problem.

  FIG. 6C shows a case where the next frame data is written during the first histogram creation process. FIG. 6C shows that the writing of the frame data # 1 has started during the first histogram creation process for the frame data # 0. Therefore, the tone of the next frame data # 1 is corrected based on only the first histogram for the frame data # 0. In this case, the gradation value search unit 13 is closest to the specific gradation value used in the previous gradation correction from the minimum gradation group and the maximum gradation group obtained from the first histogram as the specific gradation value. A value shall be selected.

  FIG. 6D shows a case where the next frame data is overtaken during the first histogram creation process. FIG. 6D shows that the writing of the frame data # 1 starts during the first histogram creation process for the frame data # 0, and an overtaking occurs at the position of the broken line B4. Therefore, the histogram creation unit 12 creates the first histogram in which frame data # 0 and frame data # 1 are mixed. Then, the gradation value search unit 13 determines a specific gradation value from the histogram created only once by the same method as described above.

  As described above, even when the writing of the frame data is not completely synchronized with the frame synchronization signal S10, the image processing unit 2 according to the present embodiment can respond immediately. Therefore, even when frame data that has been tone-corrected using the specific tone values determined by the histogram creation unit 12 and the tone value search unit 13 is displayed on the image display unit 3, the display image is greatly disturbed. Absent.

  Note that the image processing performed by creating the histogram only once can be performed in a case other than when the writing of the frame data is not synchronized with the frame synchronization signal S10. For example, when adjacent frame data is approximated, such as when the previous specific gradation value is included in the gradation group obtained by the first histogram creation, a histogram is created only once Image processing. In such a case, the specific gradation value determined from the previous frame data is close to the specific gradation value of the next frame data to be processed, so a histogram is created multiple times to determine the exact specific gradation value. do not have to. As a result, the processing circuit does not have to create the second histogram, so that power consumption can be reduced. Further, when the above processing is performed by software, the processing time can be shortened.

  In the above description, an example in which a moving image whose video source is 30 fps is displayed at 60 fps has been described as an example. However, the present invention is not limited to this. For example, when displaying a moving image with a video source of 60 fps at 60 fps, apart from reading out the image for display, the image is read out twice at a double speed during one frame period to create a histogram. May be created.

1 is a diagram illustrating a schematic configuration of an image display device according to an embodiment of the present invention. It is a figure which shows an example of the histogram of a gradation value. It is a figure which shows an example of the gradation correction | amendment using a histogram. It is a time chart which shows the flow of the signal processing in the image processing part which concerns on embodiment of this invention. It is a figure shown about the histogram creation method which concerns on embodiment of this invention. It is a figure shown about image processing in case writing is not completely synchronized with a frame synchronizing signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image generation part, 2 Image processing part, 3 Image display part, 11 Frame memory, 12 Histogram creation part, 13 Tone value search part, 14 Tone correction part, 20 Image display apparatus

Claims (7)

A frame memory for sequentially storing frame data;
When the frame data is stored in the frame memory, the frame data is read from the frame memory, and a first histogram showing a cumulative frequency distribution for each first group is created with a predetermined number of gradations as the first group. A first histogram creation unit;
An effective gradation range determining unit that determines an effective gradation range based on the created histogram;
After the creation of the first histogram, the frame data is read again from the frame memory, and the minimum gradation group or the maximum gradation group in the first group is less than the predetermined number of gradations for the effective gradation range. a second histogram creation unit that creates a second histogram indicating the cumulative frequency of the tone value of each of the second group is divided into a second group of gradation number,
When the next frame data is stored in the frame memory during the creation of the second histogram, a second histogram in which the next frame data is mixed is created, and the second histogram in which the next frame data is mixed If the accumulated frequency of the second histogram is a defective value, the tone value search for determining the tone values at both ends of the second histogram as the maximum tone value or the minimum tone value at which the accumulated frequency exceeds a predetermined value. And
An image processing apparatus comprising: a gradation correction unit that performs gradation correction of the frame data based on the maximum gradation value or the minimum gradation value. The effective gradation range is a first group of minimum gradation values exceeding a first predetermined value in a first histogram created in order from a small gradation value, or a first gradation created in order from a large gradation value. A second group of maximum gradation values exceeding a second predetermined value in one histogram;
The second histogram creation unit creates the second histogram only for the first group of the minimum gradation values or the second group of the maximum gradation values determined in the creation of the first histogram. The image processing apparatus according to claim 1, wherein:   The second histogram creating unit creates the second histogram in n times, and determines the predetermined number of gradations based on an nth root of the number of gradations of the frame data. Item 3. The image processing apparatus according to Item 1 or 2. A storage unit for storing frame data to be processed;
A reading unit for reading the stored frame data;
The said 2nd histogram preparation part produces | generates the said 2nd histogram divided into multiple times with respect to the same frame data read in multiple times, The said any one of Claim 1 to 3 characterized by the above-mentioned. Image processing apparatus. The first histogram creating means creates a histogram by grouping 16 gradation numbers for the read 256 gradation frame data,
5. The image processing apparatus according to claim 1, wherein the second histogram creating unit creates a histogram by grouping one gradation number. 6. By running on the computer,
Frame data is stored sequentially in the frame memory,
When the frame data is stored in the frame memory, the frame data is read from the frame memory, and a first histogram indicating a cumulative frequency distribution for each of the first groups is created with a predetermined number of gradations as the first group. ,
An effective gradation range is determined based on the created histogram,
After the creation of the first histogram, the frame data is read again from the frame memory, and the minimum gradation group or the maximum gradation group in the first group is less than the predetermined number of gradations for the effective gradation range. divided into a second group of gradation number to create a second histogram indicating the cumulative frequency of the tone value of each of the second group,
When the next frame data is stored in the frame memory during the creation of the second histogram, a second histogram in which the next frame data is mixed is created, and the second histogram in which the next frame data is mixed cumulative frequency of, when a defective value, the gradation value at each end of the second histogram, the cumulative frequency is determined as the maximum gradation value or the minimum tone value exceeds a predetermined value,
An image processing program that performs gradation correction of the frame data based on the maximum gradation value or the minimum gradation value. Frame data is stored sequentially in the frame memory,
When the frame data is stored in the frame memory, the frame data is read from the frame memory, and a first histogram indicating a cumulative frequency distribution for each of the first groups is created with a predetermined number of gradations as the first group. ,
An effective gradation range is determined based on the created histogram,
After the creation of the first histogram, the frame data is read again from the frame memory, and the minimum gradation group or the maximum gradation group in the first group is less than the predetermined number of gradations for the effective gradation range. divided into a second group of gradation number to create a second histogram indicating the cumulative frequency of the tone value of each of the second group,
When the next frame data is stored in the frame memory during the creation of the second histogram, a second histogram in which the next frame data is mixed is created, and the second histogram in which the next frame data is mixed cumulative frequency of, when a defective value, the gradation value at each end of the second histogram, the cumulative frequency is determined as the maximum gradation value or the minimum tone value exceeds a predetermined value,
An image processing method, wherein gradation correction of the frame data is performed based on the maximum gradation value or the minimum gradation value.

Images