WO2005106789A1 - 階調補正装置、携帯端末機器、撮像装置、携帯電話、階調補正方法及びプログラム - Google Patents
階調補正装置、携帯端末機器、撮像装置、携帯電話、階調補正方法及びプログラム Download PDFInfo
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- 238000006243 chemical reaction Methods 0.000 claims abstract description 120
- 238000012545 processing Methods 0.000 claims description 38
- 230000000694 effects Effects 0.000 claims description 32
- 230000006870 function Effects 0.000 claims description 24
- 230000008569 process Effects 0.000 claims description 13
- 238000003384 imaging method Methods 0.000 claims description 5
- 230000010365 information processing Effects 0.000 claims 1
- 238000013507 mapping Methods 0.000 description 20
- 238000010586 diagram Methods 0.000 description 18
- 230000008859 change Effects 0.000 description 9
- 238000007796 conventional method Methods 0.000 description 9
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Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
- G06T5/40—Image enhancement or restoration using histogram techniques
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
- G06T5/90—Dynamic range modification of images or parts thereof
- G06T5/94—Dynamic range modification of images or parts thereof based on local image properties, e.g. for local contrast enhancement
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/6027—Correction or control of colour gradation or colour contrast
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/62—Retouching, i.e. modification of isolated colours only or in isolated picture areas only
- H04N1/628—Memory colours, e.g. skin or sky
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/20—Special algorithmic details
- G06T2207/20024—Filtering details
- G06T2207/20032—Median filtering
Definitions
- Gradation correction device mobile terminal device, imaging device, mobile phone, gradation correction method and program
- the present invention relates to a technique for correcting a gradation of a digitized image.
- a luminance value or a density value of each pixel is calculated over the entire screen of an input image, and a pixel having the same gradation value or a gradation quantifier is calculated.
- a histogram that indicates the appearance frequency of the pixels included in the same section divided into sections smaller than the number of conversions is generated, and tone correction processing that optimizes the shape of the created histogram is performed over the entire screen.
- tone correction processing that optimizes the shape of the created histogram is performed over the entire screen.
- Patent Document 1 JP 2003-69825 A
- Patent Document 2 Japanese Patent Application Laid-Open No. 2003-299107
- Patent Document 3 JP-A-9 65252
- Non-patent Document 1 ANIL K. JAIN, "Fundamentals of Digital Image Processing Prentice-Hall International, Inc., 1989, pp. 241—244
- the histogram 601 of the low-luminance area becomes a wider gradation distribution 611 after the conversion, and the local contrast in the low-luminance area increases.
- the histogram 602 in the high-luminance area has a wider gradation distribution 612 after the conversion, and the local contrast in the high-luminance area increases.
- the power of the dark area in the bright area inside was either brighter than the light area in another dark area in the same screen, or was rounded to be the same. For this reason, there is a limit on the amount of correction between the dark part of the bright area and the bright part of the dark area.When improving the local contrast in the bright area on the screen or the dark area in the screen, Inevitably, a limit was created.
- the local contrast correction is effective for all the gradations.
- the backlight correction effect for the entire area or the entire dark area has a limit. For example, when the brightness! /, Area or dark V, area continues over an area that exceeds a predetermined multiple of the size of the divided block or the divided block determined by the filter shape in block units As for the continuous brightness, the brightness level of the area or the average brightness level of the entire area, the gradation level is maintained even after the correction, and the average brightness level after the correction does not change much compared with the level before the correction. Although the contrast of the local area is improved, the backlight compensation effect of the entire bright area or the entire dark area is limited.
- the present invention has been made to solve the above-described problems, and an object of the present invention is to make it possible to further improve local contrast in a bright area or a dark area during backlight correction. .
- the subject of the present invention is a gradation correction device that divides one screen of a digital image into a plurality of local regions and then performs gradation correction.
- An average brightness calculation unit for obtaining an average brightness for each local region
- a correction amount calculation unit for obtaining a correction amount for each local region from the average brightness for each local region
- a correction unit for each pixel from the correction amount for each local region.
- An interpolation unit for performing interpolation to a correction amount; a magnitude of the correction amount for each local region and a correction amount corresponding to a median value of all luminance gradation levels; or a correction amount for each pixel unit and the total luminance.
- One gradation conversion function is selected from a plurality of gradation conversion functions prepared in advance based on the magnitude of the correction amount corresponding to the median of the gradation levels, and the correction amount for each local region and the pixel are selected. Either the deviation of the correction amount for each unit is used as a parameter, and the brightness of each pixel is Characterized by comprising a gradation conversion unit for performing gradation correction for correcting by the selected gradation conversion function.
- the subject of the present invention has the following effects 1) to 3).
- FIG. 1 is a block diagram showing a configuration example of a tone correction device according to Embodiment 1 of the present invention.
- FIG. 2 is a diagram showing block division of an image.
- FIG. 3 is a diagram showing that a correction amount is controlled by a block average luminance value.
- FIG. 4 is a diagram showing a state of interpolation for obtaining a correction amount for each pixel.
- FIG. 5 is a diagram showing a gradation conversion curve in a low luminance area.
- FIG. 6 is a diagram showing a gradation conversion curve in a high luminance region.
- FIG. 7 is a flowchart showing a gradation correction method according to Embodiment 1 of the present invention.
- FIG. 8 is a block diagram showing a configuration example of a gradation correction device according to Embodiment 2 of the present invention.
- FIG. 9 is a flowchart showing a gradation correction method according to Embodiment 2 of the present invention.
- FIG. 10 is a diagram showing a histogram of an input image.
- FIG. 11 is a diagram showing a histogram of a converted image.
- FIG. 12 is a diagram showing a histogram of an image after conversion.
- FIG. 13 is a block diagram showing a configuration example of a tone correction device according to a third embodiment of the present invention.
- FIG. 14 is a diagram showing a mapping curve according to Embodiment 3 of the present invention.
- FIG. 15 is a view showing a straight line mapping curve.
- the feature of the present embodiment is that, after the screen is divided into a plurality of blocks, the amount of change from the average luminance level of each local region divided as a block to the corrected luminance level is calculated for the local region.
- the feature point of the present embodiment is that the average luminance level of each local region is controlled so as to be increased when the average luminance level of the local region is relatively low when viewed from the median of the ⁇ degree gradation level. The point is.
- a feature point of the present embodiment is that the average luminance level of each local region is lowered when the average luminance level of the local region is relatively high in view of the median value of all luminance gradation levels. Control in the same way.
- the feature of this embodiment is that (1) when the average luminance level of the local area is relatively low when viewed from the median of the gray scale levels, the correction amount in the luminance correction of the local area (2) When the average luminance level is high at the median power of the gray scale level, the amount of correction in the luminance correction of the local area is greatly controlled, while (3) the local area When the average luminance level of the local area is medium (approximately the entire luminance gradation level), the control is performed to reduce the correction amount in the luminance correction of the local area.
- the correction amount in the luminance correction of the local region is increased, and when the average luminance level is medium, The amount of correction in the brightness correction of the local region is reduced, and when the average brightness level is higher than the median of all the brightness gradation levels, control is performed so that the amount of correction in the brightness correction of the local region is medium.
- FIG. 1 is a block diagram illustrating a configuration or a functional unit of a tone correction device according to the present embodiment.
- digital image data input to the tone correction device is input to a correction amount calculation unit 101 and a storage unit 106.
- the correction amount calculation unit 101 performs processing in block units (local region units) under the control of the included block timing generation unit 102.
- the average luminance calculation unit 103 calculates an average luminance value for each block from the input image data.
- the block-based correction amount calculation unit 104 calculates a correction amount in block units from the input average luminance value in block units.
- the pixel unit correction amount calculation unit 105 calculates a pixel unit correction amount from the input block unit correction amount. That is, the pixel unit correction amount calculation unit 105 functions as an “interpolation unit” that performs interpolation from the correction amount for each block unit to the correction amount based on the pixel unit.
- the gradation conversion unit 107 converts the correction amount input from the pixel unit correction amount calculation unit 105 and the conversion table value of the gradation conversion table unit 108 based on the control signal output from the block timing generation unit 102. With the use of this, the same unit 107 performs gradation conversion on the image data (brightness value data) read from the storage unit 106.
- the storage unit 106 Since a delay of only one to several block lines occurs in the entire correction amount calculation unit 101, the storage unit 106 is normally configured with a line memory that generates an equivalent delay of one to several block lines. If a delay occurs in the unit of frame on the side of the correction amount calculation unit 101, the storage unit 106 is also configured by a frame memory that generates an equivalent delay of the frame unit.
- the average luminance calculating unit 103 generates an average luminance value (in units of blocks) for each block number generated by the block timing generating unit 102. (Also referred to as average luminance in a block). If the image data format is not in the luminance / chrominance format when the image data is input to the average luminance calculation unit 103, format conversion to the luminance / chrominance format is performed before calculating the average luminance. There is a need to do. In such a case, it is provided before the block for performing such format conversion or the functional unit power correction amount calculation unit 101.
- the average luminance calculation unit 103 determines the average value of RGB as the “average luminance value in block units”. Good, but in the following description, digital The image data is converted into a luminance / chrominance format in advance, and then handled as input to the correction amount calculation unit 101.
- the block timing generator 102 1) When the digital image input into the correction amount calculator 101 is a television video signal or an image signal of a digital camera module, the block timing generator 102 Synchronously, it outputs first to fourth control signals for controlling the processing of the respective units 103, 104, 105, 107. On the other hand, 2) a digital image to be input is already stored in a memory (not shown) in a certain memory (not shown), and the CPU (not shown) reads the digital image and calculates a correction amount. In the case of inputting to the unit 101, the block timing generating unit 102 controls the processing of each of the units 103, 104, 105, 107 in synchronization with the read start clock of the memory of the CPU. Outputs control signal.
- FIG. 2 is a diagram showing block division of an image.
- reference numeral 501 indicates the entire screen, and the entire screen 501 is divided into a plurality of blocks by boundary lines 502 extending vertically and horizontally. If backlight correction is performed, for example, if a large bright area and a large dark area exist in the input image, the block 503 included in the bright area in the image and the image The block 504 included in the dark area exists within the entire screen 501.
- the average luminance calculation unit 103 accumulatively adds the luminance values of the input image data in the same block area, and finally divides the luminance value of the input image data by the number of pixels in the block to calculate the average luminance value in block units. calculate.
- the number of pixels of powers of 2 in both the vertical and horizontal directions is often used for the block size. Since the block 503 in FIG. 2 is a bright area, the average luminance value of each block 503 obtained by the average luminance calculation unit 103 is a relatively high value. Conversely, since the block 504 in FIG. 2 is a dark area, the average luminance value of each block 504 obtained by the average luminance calculation unit 103 is a relatively low value.
- “information on the number of pixels” in the block to be processed (the block number is specified by the first control signal) in the same unit 103 is: 1) If it is variable information, individual For each block of the above, “information on the number of pixels” is given from the CPU (not shown) to both units 102 and 103. On the other hand, if it is a fixed value, Is stored in both parts 102 and 103.
- the average luminance value in block units obtained by the average luminance calculation unit 103 is input to the block unit correction amount calculation unit 104.
- the block unit correction amount calculation unit (also simply referred to as a correction amount calculation unit) 104 performs correction in block units according to the timing generated by the block timing generation unit 102 (processing start timing instructed by the second control signal). Calculate the direction and correction amount.
- the method for calculating the correction amount is as follows. That is, the average luminance value of a certain block (unit) to be processed in one screen, which is input to the block unit correction amount calculation unit 104, is relatively low in view of the median value of all luminance gradation levels. In this case, as shown in FIG.
- the block unit correction amount calculation unit 104 sets a large correction amount for the average luminance value of the block (unit) (in this case, sets the correction direction to plus. ), And outputs the correction amount for the relatively large block (unit) generated in this way.
- the average luminance value of each block input to the block-unit correction amount calculating unit 104 is relatively high in view of the above-mentioned median power, as shown in FIG.
- Sets the correction amount for the average luminance value of the block (unit) to be small in this case, the direction of correction is set to minus
- the correction amount in a relatively small block unit generated in this way Is output.
- FIG. 3 shows, as an example, a case where the calculation formula for controlling the correction amount based on the input average luminance value in the block is a straight line.
- the force is changed to such a straight line. May be used in the above correction formula.
- the control curve of the curve is used, the processing amount in the block unit correction amount calculation unit 104 increases, and therefore, the block unit correction amount calculation unit 104 usually includes the straight line or the straight lines.
- the processing operation of the correction direction and the correction amount is executed by the correction calculation formula including the combination.
- the “correction direction” obtained by the block-unit correction amount calculation unit 104 is set in the opposite direction, the setting of a correction curve (FIGS. 5 and 6) described later also needs to be inverted.
- the correction amount of the block (current processing target block designated by the first control signal) (block unit) output from the block unit correction amount calculation unit 104 is output to the pixel unit correction amount calculation unit 105. It is input and interpolated to the correction amount for each pixel in the block. That is, the pixel The unit correction amount calculation unit 105 includes a block unit correction amount input from the block unit correction amount calculation unit 104, and a “block number” and “block offset position” (block) input together from the block timing generation unit 102.
- the internal offset position is the position of each pixel belonging to the block defined by the position coordinate axis set at one of the four corners of each block as the origin. Correction amount "is calculated. FIG.
- reference numeral 221 denotes a position 225 of the “target pixel” to be interpolated (the positional relationship of the target pixel position 225 with respect to the center of gravity of the block is the offset position in the block to which the target pixel belongs. (Specified) is the correction amount of the block whose center of gravity is located on the upper left side.
- reference numeral 222 is on the upper right side of the target pixel position 225
- reference numeral 223 is on the lower left side of the target pixel position 225
- reference numeral 224 is on the lower right side of the target pixel position 225. This is the correction amount.
- the correction amount 226 at the position 225 of the target pixel is obtained by linear interpolation from the correction amount in block units in the four surrounding blocks, using the intra-block offset position input from the block timing generation unit 102.
- the offset coordinate of the barycentric position of the block to which the code 221 belongs is set to (0, 0)
- the offset coordinate of the barycentric position of the other three surrounding blocks is also defined based on the offset coordinate.
- the same unit 105 can calculate the coefficient value of the linear interpolation, whereby the same unit 105 can calculate the correction amount of the pixel of interest at the position 225. I can do it.
- the process of calculating the correction amount by such linear interpolation is executed for all the target pixels in the block to which the position 225 belongs.
- An example of simple linear interpolation is shown here.
- the force pixel unit correction amount calculation unit 105 may use spline interpolation, multi-order polynomial interpolation, or another interpolation method using a curve. .
- the "block unit”, which defines one block as a "local area”, is adopted.
- an integer multiple of the block size based on the block unit, or an integral multiple of the block size is used.
- an integral multiple of the integer may be used as one unit of the processing in each of the units 103 and 104.
- these units when dividing one screen of a digital image into a plurality of screens are defined as “local regions”. Therefore, one screen of a digital image
- a point that has been expressed as “pixel unit” is an integer multiple of the pixel size based on the pixel unit, or the same. May be set as "one unit” in the processing operation of the part 105.
- the correction amount for each pixel output from the pixel unit correction amount calculation unit 105 is input to the gradation conversion unit 107.
- the gradation conversion unit 107 calculates the correction amount of the pixel in the pixel unit and the luminance level of the pixel read from the storage unit 106 by the unit 107.
- the corresponding data is read from the gradation conversion table unit 108 to obtain corrected luminance data. If the correction amount obtained by the (A) pixel unit correction amount calculation unit 105 is relatively high when viewed from the central value of all luminance gradation levels, for example, FIG.
- the first conversion curve is shown in FIG.
- the first conversion curve is calculated by the pixel-unit correction amount calculation unit 105.
- the correction amount is low, for example, a second conversion curve shown in FIG. 6, which increases the gradation of the high-brightness part and widens the dynamic range of the high-brightness part, is stored.
- the gradation conversion curves of the curves as shown in FIG. 5 and FIG. 6 are illustrated, but in order to reduce the circuit scale and power consumption by simplifying the calculation, or to improve the processing speed, A combination of straight lines may be applied for gradation conversion.
- the gradation conversion section 107 may be configured to obtain the conversion table by sequential calculation by itself, or may be configured without using the conversion table.
- the correction may be performed such that the correction is performed by direct calculation from the correction amount input by the gradation conversion unit 107.
- the gradation conversion table unit 108 is an optional component, rather than an essential component.
- the gradation conversion table unit 108 is configured by, for example, a storage device or a gate circuit.
- FIG. 7 is a flowchart showing the principle of the above-described gradation correction processing.
- FIG. 7 shows each processing step in a computer-executable software program.
- an average luminance calculation step 301 an average luminance value is calculated for each block in the input image, and in a next block unit correction amount calculation step 302, the average luminance value is calculated in the correction direction.
- the next pixel unit correction amount calculation step 303 the pixel unit correction amount is calculated (interpolated) from the input block unit correction amount, and then the final gradation is calculated.
- the conversion step 304 final gradation conversion for each pixel is performed using the input correction amount for each pixel.
- the direction and amount of correction in block units are controlled by an average luminance value in block units of an input image, for example, as shown in FIG.
- the calculation of the correction amount in block units and the correction amount in pixel units are executed by, for example, linear interpolation shown in FIG.
- the gradation conversion step 304 the gradation is converted using, for example, a mating curve as shown in FIG. 5 or FIG.
- the average luminance value of a certain local area 1S which is obtained by dividing the input image into a plurality of blocks, as shown in the block 504 shown in FIG.
- the mapping curve shown in FIG. 5 is selected.
- the pixels in which the correction amount in the pixel unit calculated in the functional unit 105 or the step 303 is equal to the average luminance value 201 of the block are higher than the level 201. It is converted to a luminance level 202 corresponding to a high gradation level.
- the gradation levels of the other pixels are higher by applying FIG.
- the average luminance value 203 is converted to a luminance level 204 corresponding to a gradation level lower than the level 203.
- the tone levels near the average luminance value 203 are also converted to lower tone levels, respectively.
- the correction amount when performing the gradation correction using the mapping curves shown in FIGS. 5 and 6 is such that the average luminance value of the local area formed by dividing the input image into blocks is medium.
- the average luminance value is low, that is, when it is near the center of the grayscale level, that is, when it is near the lower limit of the grayscale level, and when the average luminance value is high, It is set to be smaller than when it is near the upper limit of the gradation level.
- the effect of the correction is reduced in the halftone level area where the gradation level was originally appropriate, and the visibility of the dark area is greatly improved. The effect is that the visibility can be improved while reducing the subjective adverse effect of the image.
- the absolute value of the correction amount when the average luminance value is low is larger than the absolute value of the correction amount when the average luminance value is high! This is particularly effective when applied to backlight correction, and is particularly effective for securing a correction amount to a dark area while making a bright area such as an image of a daytime sky look more natural.
- an image is divided into a plurality of blocks as shown in FIG.
- the image is processed after being divided into areas (local areas), and further, in step 303 (FIG. 7), a correction amount is assigned to each pixel independently, and then the gradation conversion is performed.
- step 304 (FIG. 7), a mapping curve for tone correction is selected independently for each pixel, so if the location is different, even if the tone levels are originally the same, different tone levels will be obtained after tone conversion. Can be output as
- a histogram of an input image when a low-luminance region 601 and a high-luminance region 602 are each concentrated near a specific gradation, a conventional histogram equalization method is used.
- the solid line distribution shown in FIG. 11 is obtained, and the histogram 611 of the converted low-luminance area and the histogram 612 of the high-luminance area each have a reversal of the up-down relationship of the gradation level in some gradations. Will not cause.
- the histogram 621 of the low-luminance region and the histogram 622 of the high-luminance region after conversion are partially different from each other.
- the tone can cause the up-down inversion of the gradation level.
- the dynamic range of the gradation is not changed depending on the location, but the local dynamic range is increased. Will be more widespread.
- the optimal mapping curve can be used for each of the low and high luminance areas of the image. Therefore, the dynamic range can be expanded in the low-luminance area of the image without being aware of the deterioration of the gradation characteristics in the high-luminance area.
- the dynamic range can be expanded without being conscious of the gradation characteristic deterioration in the luminance region. That is, the effect of the backlight correction can be improved.
- the degree of freedom in setting the mapping curve is increased, and it is possible to omit the processing for adjusting both the low luminance region and the high luminance region.
- the method described in the present embodiment merely changes the backlight correction method of the entire screen using the conventional histogram equalization method to the backlight correction processing in block units. It also means that it is not something.
- the conventional technique of detecting the backlight condition in the screen based on the histogram of the entire screen and correcting the backlight condition in the screen is simply a block diagram.
- the lock unit is changed, the backlight condition in the block is detected and the backlight condition in the block is corrected.
- the above-described method adopted by the apparatus according to the present embodiment does not detect the backlight state in the block and does not correct the backlight state in the block. This method corrects the backlight state between a plurality of blocks based on the average luminance value in a block. Therefore, the backlight state of the entire screen can be reduced without creating a histogram. It can be corrected.
- the entire screen can be corrected only by sequentially using the information of the local area, it is necessary to wait until the preprocessing of one entire screen is completed. It is possible to perform real-time processing without frame delay by using only a line memory that contains blocks or a line memory that is about twice or three times that of a block without the need for a frame memory in a linking circuit.
- the screen is divided into a plurality of blocks, and when the average luminance level of the local area divided into blocks is low, the correction amount in the luminance correction of the local area is increased, and the average luminance level becomes medium.
- the amount of correction in the luminance correction of the local area is reduced, so that in the area of the halftone level where the gradation level was originally appropriate, the influence of the correction is reduced while the visibility of the dark area is reduced. Can be improved.
- the correction amount in the luminance correction of the local area is increased, and the average luminance level is moderate.
- the amount of correction in local area luminance correction is reduced, and when the average luminance level is high, the amount of correction in local area luminance correction is increased. In the area of, the visibility of the dark area and the bright area can be improved while reducing the influence of the correction.
- the screen is divided into a plurality of blocks, and when the average luminance level of the local area divided into blocks is low, the correction amount in the luminance correction of the local area is increased.
- the correction amount in the local area luminance correction may be reduced, and when the average luminance level is high, the correction amount in the local area luminance correction may be set to a medium level.
- the effect of the correction is reduced in the region of the halftone level where the gradation level was originally appropriate, and the visibility of the dark region is greatly improved. In a bright area, there is an advantage that visibility can be improved while reducing a subjective adverse effect on humans due to a decrease in luminance.
- the feature of this embodiment is that the amount of change from the average luminance level of the local area to the corrected luminance level is controlled also by the average color difference vector of the local area. Furthermore, the present embodiment also controls the amount of change from the average luminance level of the local area to the corrected luminance level so that the average color difference vector of the local area becomes small when the approximate local skin color is present. It has that characteristic point.
- FIG. 8 is a diagram showing a block configuration of a tone correction device according to the present embodiment.
- the configuration of FIG. 8 differs from that of FIG. 1 only in each of the sections 109 and 110 in FIG. 8, and the other components are the same as the corresponding components in FIG.
- image data input to the tone correction device is input to the correction amount calculation unit 101A and the storage unit 106.
- the block timing generation unit 102 performs processing in block units. First, in the average luminance calculation unit 103, an average luminance value for each block of the image data is calculated. At the same time, the average color calculating unit 109 calculates an average color in block units from the image data. Next, the block-unit correction amount calculation unit 110 calculates a correction amount in block units from the average luminance value and the average color in block units. Further, the pixel unit correction amount calculation unit 105 calculates a pixel unit correction amount from the block unit correction amount. In the gradation conversion unit 107, gradation conversion is performed on the image data read from the storage unit 106 using the correction amount from the pixel unit correction amount calculation unit 105 and the gradation conversion table 108.
- the storage unit 106 Since a delay of only one to several block lines occurs in the entire correction amount calculating unit 101, the storage unit 106 is usually configured with a line memory that generates an equivalent delay of one to several block lines. If a delay in frame units occurs in the correction amount calculation unit 101, the storage unit 106 is also formed of a frame memory that generates an equivalent delay in frame units.
- the image data input to the correction amount calculation unit 101A is stored in the block timing generation unit 1
- the average luminance calculation section 103 calculates the average luminance in the block.
- the average color calculating unit 109 calculates the average color in the block. If the image data format is not in the luminance / chrominance format when the image data is input to the average luminance calculation unit 103, format conversion to the luminance / chrominance format is performed before calculating the average luminance and the average color. I do. If the RGB format is used as it is, the average value of RGB may be used as a pseudo-luminance value.However, in the following description, it is assumed that the image data is input in the luminance 'color difference format in advance. I will deal with it.
- reference numeral 501 denotes an entire screen, and the entire screen 501 is divided into a plurality of blocks by a boundary line 502. If the backlight correction is performed, for example, if the input image includes a large bright area and a dark area, a block 503 included in a bright area in the image and a block 504 included in a dark area in the image are used. Will exist.
- the average luminance calculation unit 103 calculates the average luminance in the block by cumulatively adding the luminance values of the input image data in the same block area, and finally dividing by the number of pixels in the block. .
- the number of pixels of a power of 2 is often used both in the vertical and horizontal directions as the block size. Since the block 503 in FIG. 2 is a bright area, the average luminance value output from the average luminance calculation unit 103 is a high value. Since the block 504 in FIG. 2 is a dark area, the average luminance value output by the average luminance calculation unit 103 is a low value.
- the average color calculation unit 109 calculates the average color in the block by calculating the cumulative calories of the colors of the input image data in the same block area, and finally dividing by the number of pixels in the block. .
- the number of pixels in the vertical and horizontal directions is often a power of 2 in many cases.
- a color difference in a luminance / color difference format is usually used. If the luminance 'chrominance format is Y, Cb, Cr, for example, the average value of each of Cb and Cr is obtained using two components of Cb and Cr, and the obtained average value of Cb and the average of Cr are obtained. Outputs a color vector consisting of two component values.
- this color vector is simply referred to as an average color.
- a scalar amount of a difference between the specific color and the average color in the block is obtained in advance.
- a scalar value of a specific color degree may be output instead of the color vector.
- the difference between the specific color and the color of the pixel is calculated more finely, for example, in pixel units, and finally the average of the difference values is calculated.
- the difference value may be output as a scalar value of a specific color degree.
- the scalar value of the specific color degree is simply referred to as an average color in the same manner as the color vector.
- the average color including the luminance information is calculated using both the color difference and the luminance. Is also good.
- the correction amount is calculated using both the information of the average luminance for which the luminance force was also obtained and the average color of which the color difference force was obtained.
- the luminance information and the chrominance information may be combined in the unit 110.However, if it is better to combine the luminance information and the chrominance information in pixel units in advance, the average color An average color including luminance information must be obtained in advance using both.
- the average luminance value in the block calculated by the average luminance calculation unit 103 and the average color calculated by the average color calculation unit 109 are input to the block unit correction amount calculation unit 110.
- the block-based correction amount calculation unit 110 calculates the correction amount in block units at the timing specified by the block timing generation unit 102. When the average luminance value in a block input to the block unit correction amount calculation unit 110 is low, the correction amount output from the block unit correction amount calculation unit 110 is increased as shown in FIG. Conversely, when the average intra-block luminance value input to the block unit correction amount calculation unit 110 is high, the correction amount output from the block unit correction amount calculation unit 110 is reduced as shown in FIG. Here, FIG.
- the straight line may be a curve.
- the amount of processing increases, so that control is usually performed by a straight line or a combination of straight lines. If the direction of correction is set to be reversed here, the correction curve described later must also be reversed.
- the correction amount output from the block unit correction amount calculation unit 110 is reduced as in the case of the average luminance value. .
- the correction amount output from the block unit correction amount calculation unit 110 is increased.
- This calculation formula may be a straight line, a combination of straight lines, or a curve. However, if a control curve of a curve is used, the processing amount increases. Control is performed by a combination of straight lines.
- the block-based correction amount output from the block-based correction amount calculation unit 110 is input to the pixel-based correction amount calculation unit 105.
- the pixel unit correction amount calculation unit 105 calculates the pixel unit correction amount based on the block unit correction amount input from the block unit correction amount calculation unit 110, the block number and the offset position in the block input from the block timing generation unit 102. Calculate the correction amount of.
- Figure 4 shows how interpolation is performed to determine the amount of correction for each pixel.
- Reference numeral 221 denotes a correction amount of a block whose center of gravity is located on the upper left side of the target pixel position 225.
- the upper right rule of the pixel position 222 of interest 225 and the lower left rule of the pixel position 225 of interest 223 are the correction amounts of the blocks whose centroids are located on the lower right side of the pixel position 225, respectively. It is.
- the correction amount 226 is obtained by linear interpolation from the correction amounts of the four surrounding blocks using the intra-block offset position input from the block timing generator 102.
- simple linear interpolation has been described here, spline interpolation, multi-order polynomial interpolation, or another interpolation method using a curve may be used.
- an integral multiple of the block size based on the power block unit expressed as a block unit, a fraction of an integer, or an integral multiple of an integer may be regarded as one unit.
- a point expressed as a pixel unit may be an integral multiple of a pixel size based on the pixel unit, a fraction of an integer, or an integral multiple of an integer, as one unit.
- the pixel-unit correction amount output from the pixel-unit correction amount calculation unit 105 is input to the gradation conversion unit 107.
- the gradation conversion unit 107 reads out the correction amount for each pixel and the luminance level of the pixel read from the storage unit 106 as an address of a gradation conversion table unit 108 prepared in advance, so that the corrected Data can be obtained.
- the gradation conversion table section 108 increases the gradation property of the low-luminance section as shown in FIG. 5, for example.
- the correction amount is low, the gradation range of the high-brightness part is increased and the dynamic range of the high-brightness part is widened, as shown in Fig. 6, for example.
- Various conversion curves are stored.
- FIGS. 5 and 6 the gradation conversion curves of the curves are shown. May be used. Although an example in which a conversion table is prepared in advance is shown here, a configuration in which the conversion table is obtained by sequential calculation may be used. May be performed. In addition, when the graph of the correction amount shown in FIG. 3 is reversed in the positive and negative directions, the characteristics in FIG. 5 and FIG.
- FIG. 9 is a flowchart showing the principle of the tone correction processing according to the present embodiment. Only steps 305 and 302 below are different from the processing steps in the flowchart of FIG. That is, in an average luminance and average color calculation step 305, an average luminance value and an average color are calculated for the input image in block units, and in a block unit correction amount calculation step 302, the average luminance value and the average color are calculated. A block-based correction amount is calculated, and in a pixel-based correction amount calculation step 303, a pixel-based correction amount is calculated from the input block-based correction amount, and in a gradation conversion step 304, the input pixel-based correction amount is calculated. The gradation conversion is performed using the quantity.
- the correction amount for each block is controlled by the average brightness value of each block of the input image as shown in FIG. 3, and also controlled by the average color of each block. Then, when calculating the correction amount on a block-by-block basis, the linear interpolation shown in FIG. 4 is used.
- the gradation conversion step 304 when performing gradation conversion, for example, a mapping curve as shown in FIGS. 5 and 6 is used. At this time, if the average brightness value power of each local region obtained by dividing the input image into a plurality of blocks is low as in the block 504 shown in FIG. 2, the mapping curve shown in FIG. 5 is used.
- the average luminance value 201 of the block is converted to a luminance value 202 having a higher gradation level.
- the gray level near the average luminance value is also converted to a higher gray level.
- the mapping curve shown in Fig. 6 is used.
- the average luminance value 203 of the block is converted to a luminance value 204 having a gradation level lower than that level.
- the tone levels near the average luminance value are also converted to lower tone levels, respectively.
- the average luminance level in a block is also changed, the entire high-luminance area of the image is converted to be dark, and the intuitive recognition of bright parts is improved. Can be done. That is, the effect of the backlight correction can be improved.
- the amount of correction when performing correction using the mapping curves shown in FIGS. 5 and 6 is determined when the average luminance value of a region obtained by dividing the input image into blocks is medium, When it is near the center of the gradation level, when the average luminance value is low, that is, when it is near the lower limit of the gradation level, and when the average luminance value is high, that is, it is near the upper limit of the gradation level. Set to be smaller than usual. As a result, the visibility of dark areas is greatly improved while the effect of correction is reduced in the area of the halftone level where the gradation level was originally appropriate. The effect is that visibility can be improved while reducing adverse effects.
- the absolute value of the correction amount when the average luminance value is low and larger than the absolute value of the correction amount when the average luminance value is high ! is useful when applying backlight compensation. This is particularly effective in securing a correction amount for a dark area such as a bright area such as a sky image in the daytime, while allowing the image to look more natural.
- the method described in the present embodiment performs processing by dividing an image into small regions of a plurality of blocks as shown in FIG. 2, and further, by a pixel unit correction amount calculation step 303, for each pixel.
- a correction amount is assigned independently, and in the subsequent gradation conversion step 304, a mapping curve for gradation correction is selected independently for each pixel. After the gradation conversion, they can be output as different gradation levels.
- the histogram of the input image has low-luminance regions and high-luminance regions concentrated near specific gradations
- the conventional histogram equalization method when used. Shows the distribution as shown by the solid line in FIG.
- the histogram 621 in the low-luminance area and the histogram 622 in the high-luminance area after conversion are partially gray scales, respectively. May cause the upper and lower relations of the gradation levels to be reversed.
- the conventional method using the same continuous and non-gradation-inverting mapping curve for one entire screen has a local dynamic range as compared with the case where the order of gradations does not change depending on the location. Will be more widespread.
- the optimal mapping force can be used for each of the low-brightness area and the high-brightness area of the image.
- the dynamic range can be expanded without being aware of the gradation characteristic degradation in the high brightness area, and the dynamic range can be expanded in the high luminance area of the image without being aware of the gradation characteristic degradation in the low luminance area. Can be achieved. That is, the effect of the backlight correction can be improved.
- the degree of freedom in setting the mapping curve is increased, and it is possible to omit the processing of adding a curve to both the low luminance region and the high luminance region.
- the method described in the present embodiment is obtained by simply changing the conventional backlight correction method using the histogram equalization method to a block-by-block backlight correction process. It also means that it is not. That is, conventionally, based on the histogram of the entire screen, Instead of detecting the backlight condition in the screen and correcting the backlight condition in the screen, by simply changing the block unit, the backlight condition in the block is detected and the backlight condition in the block is corrected. Will do.
- the method described in the present embodiment does not detect a backlight state in a block, nor does it correct a backlight state in a block.
- the method described in the present embodiment corrects the backlight state between a plurality of blocks based on the average luminance value in a block. Therefore, without creating a histogram, the backlight state of the entire screen is obtained as a result. Can be corrected.
- real-time processing can be performed without a frame delay by using only a line memory that includes a block or a line memory that is about twice or three times that of a block without using a frame memory in a circuit.
- the amount of correction is also controlled by the average color difference vector of the local area! / ⁇ , so that the subjective effect perceived by humans due to gradation correction for the area having a specific color is controlled. It has the effect of being able to do it.
- the subjective effect felt by humans is particularly remarkable for the flesh color of a person. Therefore, when the average color difference vector of the local region is close to the approximate flesh color, the correction amount should be set to be small. In addition, even when the image includes a portrait, there is an effect that the subjective effect of human perception on the human skin image due to the gradation correction can be reduced.
- the screen is divided into a plurality of blocks, and the amount of change from the average luminance level of the local area divided into blocks to the corrected luminance level is calculated as the local area Since the control is also made by the average color difference vector, it is possible to control the subjective effect perceived by humans due to the gradation correction over the entire area where the area having a specific color is continuously large in area. There is an advantage to say.
- the screen is divided into a plurality of blocks, and the amount of change from the average luminance level of the local region divided into blocks to the corrected luminance level is represented by the average color difference vector of the local region. Since the control is performed so as to be small when the color is near the color, there is an advantage that the subjective effect that the human perceives on the human skin image by the gradation correction can be reduced.
- the gradation conversion unit 107 performs conversion by using a conversion table corresponding to the number of levels of the correction amount.
- conversion is performed using only two types of conversion data tables.
- FIG. 13 is a diagram showing a block configuration of the tone correction device according to the present embodiment.
- the configuration of FIG. 13 differs from that of FIG. 1 in the device configuration of the portion that performs gradation conversion.
- the parts for performing the gradation conversion include a first gradation conversion unit 107A having a first conversion table unit 108A, a second gradation conversion unit 107B having a second conversion table unit 108B, and a gradation interpolation unit 1 07C power is also configured.
- the first conversion table unit 108A is provided with a mapping curve 246 in the case where the correction amount is the maximum value in the positive direction
- the second conversion table unit 108B is provided with a negative curve.
- a mapping curve 247 for the case where the correction amount becomes the maximum value in the direction is prepared.
- a luminance level for each pixel is input from storage section 106 to first gradation conversion section 107A and second gradation conversion section 107B.
- the first gradation conversion unit 107A obtains an output value corresponding to 241 shown in FIG. 14 with reference to the first conversion table unit 108A.
- the second gradation conversion unit 107B refers to the second conversion table unit 108B and obtains an output value corresponding to 242 shown in FIG.
- the tone interpolation unit 107C interpolates the tone according to the correction amount by performing weighted averaging based on the correction amount in pixel units output from the pixel unit correction amount calculation unit 105, An output level corresponding to 243 in FIG. 14 is obtained.
- a conversion table adapted to the gradation characteristics of the system can be used, and the number of conversion tables is reduced to two, so that there is an effect that the circuit scale or the program size can be reduced.
- the operation is simplified to reduce the circuit scale and power consumption.
- a combination of straight lines may be used for gradation conversion instead of a gradation conversion curve.
- the gradation conversion unit may be configured to obtain the conversion table by sequential calculation by itself, or the gradation conversion unit may receive the input without using the conversion table. The correction may be performed so that the correction is performed by direct calculation from the corrected amount.
- the calculation and comparison of the straight lines can be performed without using the first and second conversion table units 108A and 108B shown in FIG.
- the circuit scale or the program size can be reduced by the arithmetic circuit that performs the above. Specifically, the input data is subjected to gradation conversion by calculation using linear equations 256 and 257, and the smaller gradation of the output result is the converted gradation when the correction amount in the positive direction is the maximum (the first gradation conversion unit).
- the larger of the conversion results obtained by the linear equations 258 and 259 can be used as the converted gradation (the output of the second gradation converter) when the amount of correction in the negative direction is the maximum.
- the conversion table is also fixed as a calculation formula, the degree of freedom of the gradation characteristics is reduced, but the circuit scale or the program size can be further reduced as compared with the above method.
- the tone correction device according to the present invention embodied in the first or second embodiment can be realized not only as a hardware device but also as a software process as a function execution of each unit by a program. It is also possible to realize this.
- FIG. 7 or FIG. 9 of the present application also shows an application example of such a program.
- the present invention can be applied to a correction process of an image photographed in a backlight state by an imaging device. However, even when the image is not in a backlight state, the gradation is partially lost in black or white.
- the present invention can also be applied to the correction processing of a flying image.
- the present invention can also be applied to improve the visibility of a display device having a poor display.
- the present invention can be applied to any device that performs an image correction process without having an imaging device and a display device. More specifically, the tone correction device according to the present invention can be applied to a portable terminal device such as a mobile phone or a PDA, or a digital device such as a personal computer.
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EP05727555.4A EP1746539B1 (en) | 2004-04-30 | 2005-03-29 | Gradation correcting apparatus, mobile terminal device, image pickup apparatus, mobile telephone, gradation correcting method, and program |
US11/587,903 US8107123B2 (en) | 2004-04-30 | 2005-03-29 | Tone correction apparatus, mobile terminal, image capturing apparatus, mobile phone, tone correction method and program for improve local contrast in bright and dark regions |
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JP2000059629A (ja) * | 1998-08-05 | 2000-02-25 | Minolta Co Ltd | 画像処理装置のための画像補正装置、画像補正方法及び画像補正プログラムを記録した機械読取り可能な記録媒体 |
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US5715377A (en) * | 1994-07-21 | 1998-02-03 | Matsushita Electric Industrial Co. Ltd. | Gray level correction apparatus |
JP3501252B2 (ja) * | 1995-06-16 | 2004-03-02 | 三菱電機株式会社 | 階調補正装置 |
US6643398B2 (en) * | 1998-08-05 | 2003-11-04 | Minolta Co., Ltd. | Image correction device, image correction method and computer program product in memory for image correction |
US7440612B2 (en) * | 1998-11-13 | 2008-10-21 | Sony Corporation | Image processing apparatus and method capable of correcting gradation of image data |
JP3772133B2 (ja) | 2001-06-14 | 2006-05-10 | 松下電器産業株式会社 | 自動階調補正装置,自動階調補正方法および自動階調補正プログラム記録媒体 |
US6826310B2 (en) * | 2001-07-06 | 2004-11-30 | Jasc Software, Inc. | Automatic contrast enhancement |
JP4197858B2 (ja) * | 2001-08-27 | 2008-12-17 | 富士通株式会社 | 画像処理プログラム |
JP4281311B2 (ja) * | 2001-09-11 | 2009-06-17 | セイコーエプソン株式会社 | 被写体情報を用いた画像処理 |
JP2003299107A (ja) | 2002-03-29 | 2003-10-17 | Matsushita Electric Ind Co Ltd | 撮像装置 |
JP3698118B2 (ja) * | 2002-06-05 | 2005-09-21 | 三菱電機株式会社 | 色変換装置および色変換方法 |
AU2002950210A0 (en) * | 2002-07-11 | 2002-09-12 | Mediaware Solutions Pty Ltd | Mosaic construction from a video sequence |
JP4347105B2 (ja) * | 2003-04-03 | 2009-10-21 | 富士フイルム株式会社 | 画像処理方法および装置並びにデータベース並びにプログラム |
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2005
- 2005-03-29 WO PCT/JP2005/005850 patent/WO2005106789A1/ja not_active Application Discontinuation
- 2005-03-29 EP EP05727555.4A patent/EP1746539B1/en not_active Expired - Fee Related
- 2005-03-29 US US11/587,903 patent/US8107123B2/en not_active Expired - Fee Related
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JPH05328211A (ja) * | 1991-08-30 | 1993-12-10 | Matsushita Electric Ind Co Ltd | 画像処理装置 |
JPH07220066A (ja) * | 1994-01-28 | 1995-08-18 | Matsushita Electric Ind Co Ltd | 画像処理装置 |
JPH1021386A (ja) * | 1996-07-02 | 1998-01-23 | Fuji Xerox Co Ltd | 画像処理装置 |
JP2000059629A (ja) * | 1998-08-05 | 2000-02-25 | Minolta Co Ltd | 画像処理装置のための画像補正装置、画像補正方法及び画像補正プログラムを記録した機械読取り可能な記録媒体 |
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Also Published As
Publication number | Publication date |
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US20070229863A1 (en) | 2007-10-04 |
EP1746539B1 (en) | 2014-05-28 |
EP1746539A1 (en) | 2007-01-24 |
JP2005341527A (ja) | 2005-12-08 |
US8107123B2 (en) | 2012-01-31 |
EP1746539A4 (en) | 2008-07-09 |
JP3949684B2 (ja) | 2007-07-25 |
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