JP2010147969A - Image correction processing circuit and semiconductor device obtained by integrating the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image correction processing circuit capable of generating a desired output image by applying suitable image correction processing to an input image. <P>SOLUTION: The image correction processing circuit includes: an image correction section 11 for generating an output image by applying predetermined image correction processing to an input image; an arithmetic section 12 for acquiring a luminance histogram for each field of the input image and for calculating any two values or all of three values of an average luminance value, a standard deviation value and an intermediate value (an average luminance value ACAVG and a standard deviation value ACVRC in an example of Fig.1) of the luminance histogram; and a correction control section 13 for controlling the image correction section 11 by determining necessity of image correction processing to the input image or a correction amount based on any two values or all of three values of the average luminance value, the standard deviation value and the intermediate value of the luminance histogram calculated by the arithmetic section 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image correction processing circuit that performs various image correction processes on an input image to generate a desired output image, and a semiconductor device formed by integrating the image correction processing circuit.

  Conventionally, in the field of devices or systems that handle digital images (indoor / outdoor surveillance cameras, network cameras (IP cameras), Web cameras, intercoms, etc.), various image correction processing (fogging correction processing, backlight correction processing) is applied to input images. In other words, an image correction processing circuit that generates a desired output image by performing light and dark correction processing or the like is used.

  Note that the conventional image correction processing circuit generally divides one field of an input image into a plurality of areas, and what kind of scene the input image is based on a luminance histogram acquired for each area ( For example, it is determined whether it is foggy or backlit, and an optimal image correction process is performed on the input image.

Patent document 1 can be mentioned as an example of the prior art relevant to the above.
Japanese Patent No. 3981260

  Certainly, if an image correction processing circuit is used, a fogged input image or a backlight input image can be converted into an output image with higher visibility and sent to a display device.

  However, in the scene discrimination method employed in the conventional image correction processing circuit, there is a case where an appropriate scene discrimination result cannot always be obtained, and there is room for further improvement.

  In view of the above-described problems, the present invention provides an image correction processing circuit capable of generating a desired output image by performing appropriate image correction processing on an input image, and a semiconductor device formed by integrating the image correction processing circuit. The purpose is to do.

  In order to achieve the above object, an image correction processing circuit according to the present invention includes an image correction unit that performs a predetermined image correction process on an input image to generate an output image; a luminance histogram for each field of the input image; A calculation unit that acquires and calculates any two or three of the average luminance value, standard deviation value, and intermediate value; the average luminance value and standard deviation value of the luminance histogram calculated by the calculation unit; And a correction control unit that determines whether or not an image correction process is required for the input image and a correction amount based on any binary value or all three values of the intermediate value, and controls the image correction unit. (The first configuration).

  In the image correction processing circuit having the first configuration, the image correction unit performs fog image correction processing on the input image, and the correction control unit is configured to obtain an average luminance value of the luminance histogram. Based on the standard deviation value, the configuration (second configuration) may be used to determine whether or not the fog image correction processing is necessary and the correction amount.

  Further, in the second image correction processing circuit, the correction control unit has an average luminance value of the luminance histogram larger than a first threshold value, and a standard deviation value of the luminance histogram is larger than a second threshold value. When it is small, it is preferable to adopt a configuration (third configuration) for determining that the fog image correction process is necessary.

  In the image correction processing circuit having the third configuration, when the correction control unit determines that the fog image correction process is necessary, the fog image correction is performed as the standard deviation value of the luminance histogram is smaller. It is preferable to adopt a configuration (fourth configuration) in which the processing correction amount is set to be large stepwise or continuously.

  In the image correction processing circuit having the third or fourth configuration, a hysteresis width is set to at least one of the first threshold value and the second threshold value (fifth configuration). Good.

  The image correction processing circuit having any one of the first to fifth configurations externally outputs various parameters referred to by the correction control unit when determining whether or not the image correction processing is necessary for the input image. A configuration including a register for setting (sixth configuration) is preferable.

  The semiconductor device according to the present invention has a configuration (seventh configuration) in which the image correction processing circuits having any one of the first to sixth configurations are integrated.

  According to the present invention, it is possible to generate a desired output image by performing an appropriate image correction process on an input image.

  FIG. 1 is a block diagram showing an embodiment of an image processing IC according to the present invention. The image processing IC 10 of this embodiment is a semiconductor device in which an image correction processing circuit including a fog image correction unit 11, a luminance histogram calculation unit 12, a correction control unit 13, and a register 14 is integrated. is there. Although not clearly shown in FIG. 1, the image processing IC 10 has various image processing (luminance dynamic range correction, brightness correction, backlight correction, etc.) for the input image in addition to the fog image correction unit 11. It is possible to include a circuit block that applies

  The fog image correction unit 11 is a unit that performs a fog image correction process on the input image input from the image source 20 to generate a desired output image and outputs it to the display device 30. The image source 20 is a means for generating an input image input to the image processing IC 10, and for example, a digital video camera that performs moving image shooting, a digital still camera that performs still image shooting, or the like can be used. The image source 20 includes a broadcast receiver (digital television broadcast receiver, etc.) and a media playback device (video CD, DVD, Blu-ray disc, hard disk, semiconductor memory, and other drive devices having a playback function, It is also possible to use a personal computer equipped with a video content playback function provided via the Internet. The display device 30 is a means for displaying an output image that has been subjected to fog image correction processing by the image processing IC 10, and an LCD [Liquid Crystal Display], an organic EL [Electro-Luminescence] display, or the like can be used.

  The luminance histogram calculation unit 12 acquires a luminance histogram for each field (frame) of the input image input from the image source 20, and any one of the average luminance value, the standard deviation value, and the intermediate value is binary or three. It is a means for calculating all values. In the example of FIG. 1, the luminance histogram calculation unit 12 is configured to calculate the average luminance value ACAVG and the standard deviation value ACVRC of the luminance histogram.

  The correction control unit 13 is a fog image correction process for the input image based on any two or three values of the average luminance value, the standard deviation value, and the intermediate value of the luminance histogram calculated by the luminance histogram calculation unit 12. Is a means for determining the necessity and the amount of correction, and controlling the fog image correction unit 11 based on the determination result. In the example of FIG. 1, the correction control unit 13 compares the average luminance value ACAVG of the luminance histogram with the first threshold value (ACAVGTH1, ACAVGTH2), the standard deviation value ACVRC of the luminance histogram, and Determination of determining whether or not fog image correction processing is necessary and the amount of correction based on the comparison results of the second comparison unit 132 that compares the second threshold values (ACVRCTH1 to ACVRCTH3) and the first comparison unit 131 and the second comparison unit 132 Part 133. The control operation of the fog image correction unit 11 by the correction control unit 13 will be described in detail later.

  The register 14 stores various parameters (including the first threshold value and the second threshold value described above) that are referred to by the correction control unit 13 when determining whether or not the fog image correction process is necessary for the input image and the correction amount. This is parameter storage means for external setting from the microcomputer 40.

  Next, prior to explaining the operation of the correction control unit 13, it will be considered what difference occurs in each luminance histogram between the input image with fog and the input image without fog. 2A and 2B are schematic diagrams showing an input image with fog and its luminance histogram, respectively. FIGS. 3A and 3B are schematic diagrams showing an input image without fog and its luminance histogram, respectively. FIG.

  In general, an input image with fog (FIG. 2A) is generally white (brighter) and has a low contrast (narrow luminance dynamic range) compared to an input image without fog (FIG. 3A). Become. That is, the luminance histogram of the input image with fog is higher in average luminance value and smaller in standard deviation value than the luminance histogram of the input image without fog (FIG. 2B, FIG. 3B).

  In view of the above consideration, the correction control unit 13 determines whether or not the fog image correction processing is necessary for the input image and the correction amount based on the average luminance value ACAVG and the standard deviation value ACVRC of the luminance histogram calculated by the luminance histogram calculation unit 12. It is set as the structure which determines and controls the fog image correction | amendment part 11 based on the determination result.

  FIG. 4 is a flowchart for explaining the necessity determination of fog image correction processing by the correction control unit 13 (particularly the determination unit 133). At the start of this flowchart, the register value FR_AT is set to “1 (fog image correction process: automatic)”, and the register value FR_EN is set to “0 (fog image correction process: stopped)”. Shall.

  First, before describing the contents of the flowchart, the register value FR_AT and the register value FR_EN will be described in detail. The register value FR_AT is a register value for setting a method for executing fog image correction processing. When the register value FR_AT is set to “0”, the fog image correction process is executed manually. When the register value FR_AT is set to “1”, the fog image correction process is automatically executed. When the register value FR_AT is set to “1”, the bit control of the register value FR_EN (fog image correction process operation check control) is also automatically performed.

  The register value FR_EN is a register value for performing operation control (enable control) or operation confirmation of fog image correction processing. When the register value FR_AT is set to “0 (mist image correction process: manual)”, the register value FR_EN is used for operation control (enable control) of the fog image correction process. That is, when the register value FR_EN is set to “0”, the fog image correction process is disabled, and when the register value FR_EN is set to “1”, the fog image correction process is enabled. On the other hand, when the register value FR_AT is set to “1 (fog image correction process: automatic)”, the register value FR_EN is used to check the operation of the fog image correction process. That is, when the register value FR_EN is set to “0”, it is confirmed that the fog image correction process is stopped. When the register value FR_EN is set to “1”, the fog image correction process is in operation. It is confirmed that there is.

  Next, the contents of the flowchart shown in FIG. 4 will be specifically described. When this flowchart is started, in step S1, a comparison determination is made between the average luminance value ACAVG of the luminance histogram and the first threshold value (upper threshold ACAVGTH1 in step S1). If it is determined that ACAVG ≧ ACAVGTH1, the flow proceeds to step S2 (correction amount adjustment state). On the other hand, if it is determined that ACAVG ≧ ACAVGTH1, the flow proceeds to step S4.

  If it is determined in step S1 that ACAVG ≧ ACAVGTH1, in step S2, the fog image correction process in the fog image correction unit 11 is turned on (basically, the register value FR_EN = “1”), and the correction amount ( Adjustment processing is performed. The correction amount adjustment process in step S2 will be described in detail later.

  On the other hand, if it is determined in step S1 that ACAVG ≧ ACAVGTH1, it is determined in step S4 whether or not the register value FR_EN is set to “1” and the average luminance value ACAVG of the luminance histogram and the first Is compared with the threshold value (the lower threshold value ACAVGTH2 (≦ ACAVGTH1) in step S4). Here, when the register value FR_EN is set to “1” and it is determined that ACAVG ≧ ACAVGTH2, the flow proceeds to step S2 described above. On the other hand, if it is determined that the register value FR_EN is not set to “1” or that ACAVG ≧ ACAVGTH2, the flow proceeds to step S5.

  If it is determined in step S4 that the register value FR_EN is not set to “1” or that ACAVG ≧ ACAVGTH2, it is determined in step S5 that the fog image correction process in the fog image correction unit 11 is off (register value FR_EN = "0") and the flow proceeds to step S3.

  After the correction amount adjustment process is completed in step S2, or after the fog image correction process is turned off in step S5, in step S3, the register value FR_AT is set to “0 (mist image correction process: manual)”. A determination is made whether or not it has been done. If it is determined that the register value FR_AT is not set to “0”, the flow is returned to step S1, and the average luminance value ACAVG of the luminance histogram and the first threshold value (the upper threshold value in step S1). Comparison determination with ACAVGTH1) is repeated. On the other hand, when it is determined that the register value FR_AT is set to “0”, a series of flows is terminated in order to switch the fog image correction process to manual execution.

  For the first threshold value to be compared with the average luminance value ACAVG of the luminance histogram, it is desirable to set a predetermined hysteresis width by adjusting the upper threshold value ACAVGTH1 and the lower threshold value ACAVGTH2 as described above. . By setting such a hysteresis width, as shown in FIG. 5, when the fog image correction process is turned off (when the register value FR_EN = “0”), the average luminance value of the luminance histogram is set. The fog image correction process is not turned on until ACAVG reaches the upper threshold ACAVGTH1, and conversely, when the fog image correction process is turned on (when the register value FR_EN = “1”), the luminance histogram Since the fog image correction process is not turned off until the average luminance value ACAVG of the image falls below the lower threshold value ACAVGTH2, it is possible to prevent the fogging of the output image by preventing the fog image correction process from turning on / off. It becomes. Both the upper threshold ACAVGTH1 and the lower threshold ACAVGTH2 can be externally set in the register 14 from the microcomputer 40. When the upper threshold ACAVGTH1 and the lower threshold ACAVGTH2 are set to the same value, the above hysteresis is set. The function is turned off.

  Next, the correction amount adjustment processing in step S2 will be described in detail with reference to FIG. 6A. FIG. 6A is a diagram illustrating an example of the correction amount adjustment process. The horizontal axis of FIG. 6A shows the standard deviation value ACVRC of the luminance histogram, and the vertical axis of FIG. 6A shows the register value FRADJ for setting the correction amount (correction intensity) of the fog image correction process. It is shown.

  In the correction amount adjustment process in step S2, the correction control unit 13 performs a comparison determination between the standard deviation value ACVRC of the luminance histogram and the second threshold value (ACVRCTH1 to ACVRCTH3, ACVRCTHx to ACVRCTHz), and the fog image for the input image Whether correction processing needs to be performed and, if fog image correction processing needs to be performed on the input image, which of the register values FRADJ1 to FRADJ5 should set the correction amount (correction strength) Judgment is made.

  Of the second threshold values, three threshold values (ACVRCTH1, ACVRCTH2, ACVRCTH3) can be externally set in the register 14 from the microcomputer 40, and the remaining three threshold values (ACVRCTHx, ACVRCTHy, ACVRCTHz) are The threshold value ACVRCTH1 and the threshold value ACVRCTH2 are automatically set in the form of being divided into four equal parts. Therefore, when the three threshold values (ACVRCTH1, ACVRCTH2, and ACVRCTH3) among the second threshold values are externally set, it is necessary to satisfy the relationship of ACVRCTH1 + 4 ≦ ACVRCTH2 ≦ ACVRCTH3.

  Further, the register values FRADJ1 to FRADJ5 that are correction value candidate values can also be externally set in the register 14 from the microcomputer 40. When register values FRADJ1 to FRADJ5 are set externally, FRADJ5 ≧ FRADJ4 ≧ FRADJ2 ≧ FRADJ2 ≧ FRADJ5 ≧ FRADJ2 ≧ FRADJ5 ≧ FRADJ2 ≧ FRADJ2 ≧ FRADJ2 ≧ FRADJ2 ≧ FRADJ3 ≧ FRADJ2 ≧ FRADJ5 ≧ FRADJ3 ≧ FRADJ2 ≧ It is necessary to satisfy the relationship FRADJ1 (where FRADJ5> FRADJ1).

  Note that it is desirable to set a predetermined hysteresis width for the second threshold values (ACVRCTH1 to ACVRCTH3, ACVRCTHx to ACVRCTHz) as well as the first threshold values (ACAVGTH1 and ACAVGTH2) described above. For example, as shown in FIG. 6A, when the standard deviation value ACVRC of the luminance histogram is gradually reduced (when it is necessary to increase the correction amount), the correction amount is adjusted along the path indicated by the solid line. When the standard deviation value ACVRC of the histogram gradually increases (when the correction amount needs to be reduced), the correction amount may be adjusted along the path indicated by the broken line.

  For example, consider a case where ACVRC = ACVRCTHy is determined at the previous comparison determination, and the current correction amount is set to the register value FRADJ3. In this case, the correction amount is not switched to the register value FRADJ4 until the standard deviation value ACVRC of the luminance histogram falls below the threshold value ACVRCTHx (see the solid line in FIG. 6A). Conversely, the standard deviation value ACVRC of the luminance histogram is the threshold value ACAVGTHz. The correction amount is not switched to the register value FRADJ2 until the above is reached (see the broken line in FIG. 6A). Therefore, it is possible to prevent the fog image correction processing from being frequently switched, and to suppress flickering of the output image.

  When the fog image correction process is turned off, the fog image correction process is turned on when the standard deviation value ACVRC of the luminance histogram falls below the threshold value ACVRCTH2, and the correction according to the standard deviation value ACVRC of the luminance histogram is performed. The amount adjustment process is started (see the solid line in FIG. 6A). On the other hand, after the fog image correction process is once turned on, even if the standard deviation value ACVRC of the luminance histogram is equal to or greater than the threshold value ACVRCTH2, the fog image correction process is maintained in the on state, and the standard deviation value ACVRC is equal to or greater than the threshold value ACVRCTH3. At that time, the fog image correction process is turned off (see the broken line in FIG. 6A). Therefore, the on / off oscillation of the fog image correction process can be prevented and flickering of the output image can be suppressed. When the threshold value ACVRCTH3 is set to the maximum value that can be taken by the standard deviation value ACVRC of the luminance histogram, the fog image correction process is always turned on.

  As described above, in the image processing IC 10 of the present embodiment, the correction control unit 13 determines that the average luminance value ACAVG of the luminance histogram is greater than the first threshold value (the threshold value ACAVGTH1 or the threshold value ACAVGTH2 in the examples of FIGS. 4 and 5). When it is large and the standard deviation value ACVRC of the luminance histogram is smaller than the second threshold value (threshold value ACVRCTH2 or ACVRCTH3 in the example of FIG. 6A), it is determined that fog image correction processing is necessary. As described above, if the configuration for determining whether or not the fog image correction process is required for the input image and the correction amount based on the average luminance value ACAVG and the standard deviation value ACVRC of the luminance histogram, the area division process of the input image is not required. Appropriate scene discrimination can be performed and optimal fog image correction processing can be performed for each scene, so that the visibility of the output image can be improved.

  Note that the necessity of the fog image correction process and the correction amount determination process described above are performed for each field (frame) of the input image. Based on the determination result, the instruction content to the fog image correction unit 11 is changed. The frequency of updating is not necessarily limited to one field, and can be arbitrarily adjusted according to the register setting from the microcomputer 40, such as every 16 fields, every 32 fields, or every 64 fields.

  Further, by performing software calculation processing using the microcomputer 40, it is possible to perform the fog image correction processing described above, determination of necessity thereof, and adjustment of the correction amount. However, the image processing IC 10 according to the present invention is used. If hardware arithmetic processing is performed, the load on the microcomputer 40 can be reduced, so that the processing speed can be improved and the cost can be reduced as a whole system.

  In the above-described embodiment, the configuration in which the present invention is applied to the fog image correction processing circuit has been described as an example. However, the application target of the present invention is not limited to this, and other image correction is performed. The present invention can be widely applied to processing circuits. For example, if the present invention is applied to the backlight image correction processing circuit, a luminance histogram is acquired for each frame of the input image, the average luminance value is relatively low, the standard deviation value is relatively large, and If the intermediate value is relatively high, the input image may be recognized as being backlit and the backlight correction process may be performed.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  For example, in the above embodiment, when the correction control unit 13 determines that the fog image correction process is necessary, the correction amount of the fog image correction process is set to increase stepwise as the standard deviation value ACVRC of the luminance histogram is smaller. The configuration of the present invention (see FIG. 6A) has been described as an example, but the configuration of the present invention is not limited to this. For example, the smaller the standard deviation value ACVRC of the luminance histogram is, the fog image correction processing is. The correction amount may be set continuously large (see FIG. 6B).

  INDUSTRIAL APPLICABILITY The present invention is useful for improving the visibility of an output image in an image correction processing circuit that performs various image correction processes on an input image to generate a desired output image and a semiconductor device in which the input image is integrated. Technology.

These are block diagrams which show one Embodiment of the image processing IC which concerns on this invention. These are the schematic diagrams which show the image which has fog. These are the schematic diagrams which show the brightness | luminance histogram of the image which has fog. These are the schematic diagrams which show the image which is not fogged. These are the schematic diagrams which show the brightness | luminance histogram of the image which is not fogged. These are the flowcharts for demonstrating the necessity determination of fog image correction processing. These are figures for demonstrating the comparison determination operation | movement with the average luminance value ACAVG of a luminance histogram, and 1st threshold value (ACAVGTH1, ACAVGTH2). These are figures which show an example of a correction amount adjustment process. These are figures which show another example of a correction amount adjustment process.

Explanation of symbols

10 Image processing IC (semiconductor device)
DESCRIPTION OF SYMBOLS 11 Fog image correction | amendment part 12 Luminance histogram calculating part 13 Correction | amendment control part 131 1st comparison part 132 2nd comparison part 133 Judgment part 14 Register 20 Image source (imaging device etc.)
30 Display devices (liquid crystal display, etc.)
40 Microcomputer

Claims (7)

An image correction unit that performs a predetermined image correction process on the input image to generate an output image;
A calculation unit that acquires a luminance histogram for each field of the input image and calculates any two or three values of the average luminance value, the standard deviation value, and the intermediate value;
The necessity or amount of image correction processing for the input image is determined based on any two or three of the average luminance value, standard deviation value, and intermediate value of the luminance histogram calculated by the arithmetic unit. A correction control unit that controls the image correction unit;
An image correction processing circuit comprising: The image correction unit performs fog image correction processing on the input image,
The image correction according to claim 1, wherein the correction control unit determines whether or not the fog image correction processing is necessary and a correction amount based on an average luminance value and a standard deviation value of the luminance histogram. Processing circuit.   The correction control unit needs the fog image correction processing when the average luminance value of the luminance histogram is larger than a first threshold value and the standard deviation value of the luminance histogram is smaller than a second threshold value. The image correction processing circuit according to claim 2, wherein the image correction processing circuit is determined.   When the correction control unit determines that the fog image correction process is necessary, the correction amount of the fog image correction process is set to be larger stepwise or continuously as the standard deviation value of the luminance histogram is smaller. The image correction processing circuit according to claim 3.   5. The image correction processing circuit according to claim 3, wherein a hysteresis width is set in at least one of the first threshold value and the second threshold value. 6.   5. A register for externally setting various parameters referred to by the correction control unit when determining whether or not an image correction process is required for the input image and a correction amount. Item 6. The image correction processing circuit according to Item 5.   7. A semiconductor device comprising the image correction processing circuit according to claim 1 integrated therein.

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