CN110400259A - The automotive number plate image inclination angle correction system and method rotated based on least square method and coordinate - Google Patents
The automotive number plate image inclination angle correction system and method rotated based on least square method and coordinate Download PDFInfo
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Abstract
The present invention provides a kind of automotive number plate image inclination angle correction system rotated based on least square method and coordinate, comprising: edge calculations unit, Dip countion unit and rotation computing unit；Edge calculations unit is used to calculate the edge pixel point of automotive number plate image；Dip countion unit is for calculating automotive number plate image inclination angle；Rotation computing unit is for correcting inclined automotive number plate image to straight.Edge calculations unit includes: automotive number plate Image Edge-Detection, the determination of automotive number plate image detection region；Dip countion unit includes: sample, the automotive number plate image Dip countion for choosing automotive number plate image Dip countion；Rotating computing unit includes: automotive number plate image positive rotation, automotive number plate image reverse rotation；The present invention can be improved the recognition accuracy of number plate of vehicle, and progress improves the functional performance of traffic technique monitoring device.
Description
Technical field
The present invention relates to field of intelligent transportation technology, especially a kind of motor vehicle rotated based on least square method and coordinate
Number plate image inclination angle correction system and method.
Background technique
In China, automotive number plate is the permission motor vehicle road within the territory of the People's Republic of China of public security traffic control department registration
The legal mark of road traveling.The earliest automotive number plate in China appears in letter out thread 27 years, experienced after founding of New more
Secondary change, become nowadays " 92 formula " automotive number plate, wherein Technical specifications are " People's Republic of China's motor vehicles
Number plate " (GA36), standard makees the contents such as the classification of automotive number plate, specification, color, the scope of application, style, technical requirements
Clear stipulaties.Recent decades, with the development of intelligent transport technology, many traffic technique monitoring cameras are installed in China on road
Machine capture and identification automotive number plate, and then manage vehicle driver.But in practice, video camera installation member is usually due to wind
It blows or vehicle driving shakes the influence accumulated over a long period to roadbed, the normal microdisplacement of video camera installation member causes its clapped vehicle number
The inclination of board image, trick-plate character identification result have an adverse effect.
In this context, the present invention proposes a kind of automotive number plate image inclination angle rotated based on least square method and coordinate
Correction system and method, first correction inclination number plate image identify number plate character again, can avoid above-mentioned wind or roadbed vibration to taking the photograph
The adverse effect of camera installation member improves video camera to automotive number plate recognition accuracy.
Summary of the invention
It is an object of the invention to overcome existing traffic technique supervision equipment in shooting automotive number plate obliquity effects, propose
A kind of automotive number plate image inclination angle correction system and method based on least square method and coordinate rotation, improves number plate of vehicle
Recognition accuracy further increases the performance of traffic technique monitoring device.The technical solution adopted by the present invention is that:
A kind of automotive number plate image inclination angle correction system rotated based on least square method and coordinate, comprising: edge meter
Calculate unit, Dip countion unit and rotation computing unit；
Edge calculations unit is used to calculate the edge pixel point of automotive number plate image；
Dip countion unit is for calculating automotive number plate image inclination angle；
Rotation computing unit is for correcting inclined automotive number plate image to straight.
Further,
Edge calculations unit includes: automotive number plate Image Edge-Detection, the determination of automotive number plate image detection region；
Automotive number plate Image Edge-Detection: automotive number plate image is first gone into gray space from color space, then is counted
The horizontal gradient for calculating automotive number plate gray level image obtains automotive number plate edge image；
Automotive number plate image detection region determines: according to the feature of automotive number plate edge image, from upper and lower, left and right
Four direction determines automotive number plate detection zone；
Dip countion unit includes: the sample for choosing automotive number plate image Dip countion, automotive number plate image inclination angle
It calculates；
It chooses the sample of automotive number plate image Dip countion: choosing representative edge picture in automotive number plate edge image
Sample of the vegetarian refreshments as Dip countion；
Automotive number plate image Dip countion: according to selected sample, automotive number plate image is sought by least square method
Inclination angle；
Rotating computing unit includes: automotive number plate image positive rotation, automotive number plate image reverse rotation；
Automotive number plate image positive rotation: according to the inclination angle rotate automotive number plate image coordinate, establish rotation before and
Postrotational coordinate mapping relations, rotated image coordinate pixel value is according to mapping relations by coordinate picture corresponding before image rotation
Element value assignment；
Automotive number plate image reverse rotation: for the null point in rotated image, by the coordinate opposite direction of null point rotate to
Original image is established the coordinate mapping relations after rotation and before rotation, and is repaired according to mapping to automotive number plate image bilinear interpolation
Just.
A kind of automotive number plate image inclination angle antidote rotated based on least square method and coordinate, including following step
It is rapid:
Step 1, automotive number plate color image is transformed to automotive number plate gray level image；
Step 2, the horizontal gradient for calculating automotive number plate gray level image obtains automotive number plate edge image；
Step 3, according to the feature of automotive number plate edge image, from upper and lower, left and right, four direction determines motor-driven license number
Board detection zone；
Step 4, sample of the representative edge pixel as Dip countion is chosen in automotive number plate edge image；
Step 5, according to selected sample, automotive number plate image inclination angle is sought by least square method；
Step 6, automotive number plate image coordinate is rotated according to the inclination angle, establishes and rotates the mapping of preceding and postrotational coordinate
Relationship, rotated image coordinate pixel value is according to mapping relations by coordinate pixel value assignment corresponding before image rotation；
Step 7, for the null point in rotated image, the coordinate opposite direction of null point is rotated to original image, after establishing rotation
With the coordinate mapping relations before rotation, and according to mapping to automotive number plate image bilinear interpolation correct.
The present invention has the advantages that
(1) automotive number plate edge pixel point is identified by horizontal gradient, operand is low, and accuracy rate is high.
(2) by precisely identifying number plate of vehicle region, number plate pixel is paid close attention to, other non-motor vehicle number plates are reduced
The interference of image slices vegetarian refreshments, improves anti-interference.
(3) by choosing the representative edge pixel of automotive number plate edge image as least square method sample computer
Motor-car number plate image inclination angle, reduces the complexity and operand of operation.
(4) it rotates automotive number plate image by coordinate transform to achieve the purpose that correct automotive number plate, and by interpolation
Processing method is smoothly influenced because of rotation bring vacancy, improves the effect of automotive number plate image flame detection correction.
Detailed description of the invention
Fig. 1 is system composition schematic diagram of the invention.
Fig. 2 is automotive number plate color image schematic diagram of the invention.
Fig. 3 is automotive number plate gray level image schematic diagram of the invention.
Fig. 4 is automotive number plate edge image schematic diagram of the invention.
Fig. 5 is automotive number plate of the invention minimum detection administrative division map up and down
Fig. 6 is automotive number plate representative edge pixel schematic diagram of the invention.
Fig. 7 is automotive number plate image coordinate positive rotation effect picture of the invention.
Fig. 8 is to Fig. 7 image coordinate reverse rotation interpolation effect picture.
Specific embodiment
Below with reference to specific drawings and examples, the invention will be further described.
As shown in Figure 1, a kind of automotive number plate image inclination angle correction system rotated based on least square method and coordinate, packet
It includes: edge calculations unit 10, Dip countion unit 20 and rotation computing unit 30；
Edge calculations unit 10 is used to calculate the edge pixel point of automotive number plate image；
Dip countion unit 20 is for calculating automotive number plate image inclination angle；
Rotation computing unit 30 is for correcting inclined automotive number plate image to straight.
Edge calculations unit 10 includes: automotive number plate Image Edge-Detection, the determination of automotive number plate image detection region；
Automotive number plate Image Edge-Detection: automotive number plate image is first gone into gray space from color space, then is counted
The horizontal gradient for calculating automotive number plate gray level image obtains automotive number plate edge image；
Automotive number plate image detection region determines: according to the feature of automotive number plate edge image, from upper and lower, left and right
Four direction determines automotive number plate detection zone；
Dip countion unit 20 includes: that sample, the automotive number plate image of selection automotive number plate image Dip countion incline
Angle calculates；
It chooses the sample of automotive number plate image Dip countion: choosing representative edge picture in automotive number plate edge image
Sample of the vegetarian refreshments as Dip countion；
Automotive number plate image Dip countion: according to selected sample, automotive number plate image is sought by least square method
Inclination angle；
Rotating computing unit 30 includes: automotive number plate image positive rotation, automotive number plate image reverse rotation；
Automotive number plate image positive rotation: according to the inclination angle rotate automotive number plate image coordinate, establish rotation before and
Postrotational coordinate mapping relations, rotated image coordinate pixel value is according to mapping relations by coordinate picture corresponding before image rotation
Element value assignment；
Automotive number plate image reverse rotation: for the null point in rotated image, the coordinate after rotation and before rotation is established
Mapping relations, and automotive number plate image bilinear interpolation is corrected according to mapping.
The automotive number plate image inclination angle antidote rotated based on least square method and coordinate, comprising the following steps:
Step 1, automotive number plate color image image gray-scale transformation: is transformed to automotive number plate gray level image；
At false coordinate (i, j), automotive number plate color image pixelR, G, B component be respectivelyWithWith position gray level image pixel valueIt converts as follows:
Such as: Fig. 2 is automotive number plate color image I1, and Fig. 3 is automotive number plate gray level image I2；
Step 2, edge detection: the horizontal gradient for calculating automotive number plate gray level image obtains automotive number plate edge graph
Picture；
Since automotive number plate horizontal direction aspect ratio characteristic is obvious, according to automotive number plate gray level image I2
Horizontal gradient, calculate automotive number plate edge image I3, formula is as follows:
Wherein th1 is threshold value: if automotive number plate pixel horizontal gradient is not less than th1, for edge pixel point；
Such as: Fig. 4 is automotive number plate edge image, and white pixel point is automotive number plate edge pixel point；
Step 3, it region detection: according to the feature of automotive number plate edge image, is determined from upper and lower, left and right four direction
Automotive number plate detection zone；
(1) up-and-down boundary: assuming that W1And H1Respectively I3 ranks size, row scanning I3, from top scanning inspection down line by line
Coboundary up is surveyed, from least significant end up Scanning Detction lower boundary down line by line；
Wherein th2 is threshold value: it is progressively scanned down from top, when certain row has th2 or more white point, then and the line number of the row
For up；It is up progressively scanned from least significant end, when certain row has th2 or more white point, then the line number of the row is down；
(2) right boundary: column scan I3, turn right Scanning Detction left margin left by column from the leftmost side, by column from right end
Turn left Scanning Detction right margin right；
Wherein th3 is threshold value: it turns right and scans by column from left end, when certain shows th3 or more white point, then and the columns of the column
For left；It turns left and scans by column from right end, when certain shows th3 or more white point, then the columns of the column is right；
Such as: the white box in Fig. 5 is the detection zone that up, down, left and right of automotive number plate are determined；
Step 4, it chooses Dip countion sample: choosing representative edge pixel in automotive number plate edge image and be used as and incline
The sample that angle calculates；
In automotive number plate edge image I3 left margin left, right margin right, coboundary up, lower boundary down range
It is interior, while meeting the edge pixel point of formula (5) principle 1, principle 2 and principle 3, it is Dip countion sample；
Such as: white point is the Dip countion sample chosen according to formula (5) in Fig. 6；
Step 5, according to selected sample, automotive number plate image inclination angle Dip countion: is sought by least square method；
Assuming that formula (5) inclination angle sample point has m, row coordinate xk: k=1,2 ... m, column coordinate yk: k=1,2 ... m, point
Cloth in the two sides straight line y=ax+b, be slope, b is intercept, according to principle of least square method, it is as follows to establish objective function:
Seeking partial derivative respectively to a and b is zero:
Automotive number plate image inclination angle theta=(a/ π) * 180；
Step 6, image positive rotation: rotating automotive number plate image coordinate according to the inclination angle, establishes before rotation and rotates
Coordinate mapping relations afterwards, rotated image coordinate pixel value is according to mapping relations by coordinate pixel value corresponding before image rotation
Assignment；
(1) figure-number coordinate transform: when initially setting up the preceding automotive number plate image coordinate of rotation and rotation between mathematical coordinates
Mapping relations are defined as figure-number coordinate transform；Assuming that coordinate system is image coordinate system, rotation before automotive number plate image rotation
When coordinate system be mathematical coordinates system, image coordinate mooring points (0.5W1,0.5H1) it is mathematical coordinates system origin (0,0), image coordinate system
Point (i, j) and mathematical coordinates mooring pointsMapping relations are as follows:
(2) coordinate rotates；Secondly automotive number plate image is rotated in mathematical coordinates system；Postulated pointAround origin
(0,0) rotates θ counterclockwise, and rotation recoil is designated asIt establishesWithMapping relations are as follows:
(3) number-figure coordinate transform: after establishing mathematical coordinates when rotating again and rotating between automotive number plate image coordinate
Mapping relations are defined as the coordinate transform of number-figure；Assuming that coordinate system where rotated image is new images coordinate system, W2And H2It is new
Picture altitude and width, mathematical coordinates system origin (0,0) is new images coordinate system midpoint (0.5W after rotation when rotation2,0.5H2),
New images coordinate mooring pointsWith mathematical coordinates mooring pointsMapping relations are as follows:
(4) pixel assignment: after above-mentioned figure-number coordinate transform, coordinate rotation and the coordinate transform of number-figure, machine after rotation
The coordinate of motor-car number plate imagePreceding coordinate (i, j) mapping relations are as follows with rotating:
Assuming that image is I4 after automotive number plate image rotation, when formula (12)WithWhen being simultaneously integer, pixel is assigned
It is worth as follows:
When formula (12)OrWhen not being integer, since image coordinate is integer,It is then non-image coordinate, rotation
Pixel value at coordinate (i, j) before turningIt cannot be mapped as pixel value after rotating
When each coordinate of rotated image I4When mapping can be established with original image I1 coordinate (i, j),
When rotated image I4 coordinateWhen mapping can not be established with original image I1 coordinate (i, j), picture at the coordinate
Element value is null point；
Such as: Fig. 7 is the effect picture after image positive rotation, and wherein black color dots are null point.
Step 7, image reverse rotation: for the null point in rotated image, the coordinate opposite direction of null point being rotated to original image,
The coordinate mapping relations after rotation and before rotation are established, and automotive number plate image bilinear interpolation is corrected according to mapping；
(1) figure-mathematical coordinates transformation: with step 6 (3) on the contrary, establishingWithMapping relations:
(2) coordinate rotate: with step 6 (2) on the contrary,θ is rotated clockwise around origin (0,0), rotation recoil is designated asIt establishesWithMapping relations are as follows:
(3) number-figure coordinate transform: with step 6 (1) on the contrary, establishingWith (i, j) mapping relations:
(4) picture element interpolation: after above-mentioned figure-number coordinate transform, coordinate rotation and the coordinate transform of number-figure, machine after rotation
Coordinate (i, j) and coordinate after rotation before the rotation of motor-car number plate imageIt is as follows with mapping relations:
Similar with step 6, when the i or j of formula (17) are not integer, (i, j) is then non-image coordinate, it is assumed thatFor the upper left nearest with (i, j), upper right, lower-left, the pixel of bottom right 4,WithRow distance
For c, column distance d, estimated with bilinear interpolation methodIt is worth as follows:
Such as: Fig. 8 is to Fig. 7 image coordinate reverse rotation interpolation effect picture.
In conclusion a kind of automotive number plate image inclination angle rotated based on least square method and coordinate proposed by the present invention
Antidote precisely identifies number plate of vehicle region by reducing number plate of vehicle detection zone；By choosing automotive number plate edge
The representative edge pixel of image reduces the complexity of operation as least square method sample computer motor-car number plate image inclination angle
Degree and operand；It rotates automotive number plate image by coordinate transform to achieve the purpose that correct automotive number plate, and by interpolation
Processing method is smoothly because rotation bring vacancy influences.The method overcome number plate of vehicle occurs because of weather or road conditions to incline
Oblique influence improves the recognition accuracy of number plate of vehicle, also improves the functional performance of traffic technique monitoring device.
Finally it should be noted that the above specific embodiment is only used to illustrate the technical scheme of the present invention and not to limit it, to the greatest extent
Pipe is described the invention in detail referring to example, those skilled in the art should understand that, it can be to of the invention
Technical solution is modified or replaced equivalently, and without departing from the spirit and scope of the technical solution of the present invention, should all be covered
In scope of the presently claimed invention.
Claims (9)
1. a kind of automotive number plate image inclination angle correction system rotated based on least square method and coordinate, which is characterized in that packet
It includes: edge calculations unit, Dip countion unit and rotation computing unit；
Edge calculations unit is used to calculate the edge pixel point of automotive number plate image；
Dip countion unit is for calculating automotive number plate image inclination angle；
Rotation computing unit is for correcting inclined automotive number plate image to straight.
2. the automotive number plate image inclination angle correction system rotated as described in claim 1 based on least square method and coordinate,
It is characterized in that,
Edge calculations unit includes: automotive number plate Image Edge-Detection, the determination of automotive number plate image detection region；
Automotive number plate Image Edge-Detection: automotive number plate image is first gone into gray space, then computer from color space
The horizontal gradient of motor-car number plate gray level image obtains automotive number plate edge image；
Automotive number plate image detection region determines: according to the feature of automotive number plate edge image, from upper and lower, left and right four
Direction determines automotive number plate detection zone；
Dip countion unit includes: sample, the automotive number plate image Dip countion for choosing automotive number plate image Dip countion；
It chooses the sample of automotive number plate image Dip countion: choosing representative edge pixel in automotive number plate edge image
Sample as Dip countion；
Automotive number plate image Dip countion: according to selected sample, automotive number plate image inclination angle is sought by least square method；
Rotating computing unit includes: automotive number plate image positive rotation, automotive number plate image reverse rotation；
Automotive number plate image positive rotation: rotating automotive number plate image coordinate according to the inclination angle, establishes before rotation and rotates
Coordinate mapping relations afterwards, rotated image coordinate pixel value is according to mapping relations by coordinate pixel value corresponding before image rotation
Assignment；
Automotive number plate image reverse rotation: for the null point in rotated image, the coordinate opposite direction of null point being rotated to original image,
The coordinate mapping relations after rotation and before rotation are established, and automotive number plate image bilinear interpolation is corrected according to mapping.
3. a kind of automotive number plate image inclination angle antidote rotated based on least square method and coordinate, which is characterized in that packet
Include following steps:
Step 1, automotive number plate color image is transformed to automotive number plate gray level image；
Step 2, the horizontal gradient for calculating automotive number plate gray level image obtains automotive number plate edge image；
Step 3, according to the feature of automotive number plate edge image, from upper and lower, left and right, four direction determines that automotive number plate is examined
Survey region；
Step 4, sample of the representative edge pixel as Dip countion is chosen in automotive number plate edge image；
Step 5, according to selected sample, automotive number plate image inclination angle is sought by least square method；
Step 6, automotive number plate image coordinate is rotated according to the inclination angle, establishes before rotation and the mapping of postrotational coordinate is closed
System, rotated image coordinate pixel value is according to mapping relations by coordinate pixel value assignment corresponding before image rotation；
Step 7, for the null point in rotated image, the coordinate opposite direction of null point is rotated to original image, establishes after rotation and revolves
Coordinate mapping relations before turning, and automotive number plate image bilinear interpolation is corrected according to mapping.
4. the automotive number plate image inclination angle antidote rotated as claimed in claim 3 based on least square method and coordinate,
It is characterized in that,
In step 2, according to the horizontal gradient of automotive number plate gray level image I2, automotive number plate edge image I3 is calculated, formula is such as
Under:
Wherein th1 is threshold value: if automotive number plate pixel horizontal gradient is not less than th1, for edge pixel point.
5. the automotive number plate image inclination angle antidote rotated as claimed in claim 4 based on least square method and coordinate,
It is characterized in that,
Step 3 specifically includes:
(1) up-and-down boundary: assuming that W1And H1Respectively I3 ranks size, row scanning I3, from top line by line down on Scanning Detction
Boundary up, from least significant end up Scanning Detction lower boundary down line by line；
Wherein th2 is threshold value: being progressively scanned down from top, when certain row has th2 or more white point, then the line number of the row is
up；It is up progressively scanned from least significant end, when certain row has th2 or more white point, then the line number of the row is down；
(2) right boundary: column scan I3, turn right Scanning Detction left margin left by column from the leftmost side, turns left by column from right end
Scanning Detction right margin right；
Wherein th3 is threshold value: turning right and scans by column from left end, when certain shows th3 or more white point, then the columns of the column is
left；It turns left and scans by column from right end, when certain shows th3 or more white point, then the columns of the column is right.
6. the automotive number plate image inclination angle antidote rotated as claimed in claim 5 based on least square method and coordinate,
It is characterized in that,
Step 4 specifically includes: in automotive number plate edge image I3 left margin left, right margin right, coboundary up, following
Within the scope of boundary down, while meeting the edge pixel point of formula (5) principle 1, principle 2 and principle 3, is Dip countion sample；
7. the automotive number plate image inclination angle antidote rotated as claimed in claim 6 based on least square method and coordinate,
It is characterized in that,
Step 5 specifically includes:
Assuming that inclination angle sample point has m, row coordinate xk: k=1,2 ... m, column coordinate yk: k=1,2 ... m are distributed in straight line y=
The two sides ax+b, it is slope, b is intercept, according to principle of least square method, it is as follows to establish objective function:
Seeking partial derivative respectively to a and b is zero:
Automotive number plate image inclination angle theta=(a/ π) * 180.
8. the automotive number plate image inclination angle antidote rotated as claimed in claim 7 based on least square method and coordinate,
It is characterized in that,
Step 6 specifically includes:
(1) it figure-number coordinate transform: is mapped between mathematical coordinates when initially setting up the preceding automotive number plate image coordinate of rotation and rotation
Relationship is defined as figure-number coordinate transform；Assuming that coordinate system is image coordinate system before automotive number plate image rotation, when rotation, is sat
Mark system is mathematical coordinates system, image coordinate mooring points (0.5W1,0.5H1) it is mathematical coordinates system origin (0,0), image coordinate mooring points
(i, j) and mathematical coordinates mooring pointsMapping relations are as follows:
(2) coordinate rotates；Secondly automotive number plate image is rotated in mathematical coordinates system；Postulated pointAround origin (0,0)
Rotation θ counterclockwise, rotation recoil are designated asIt establishesWithMapping relations are as follows:
(3) it number-figure coordinate transform: is mapped between automotive number plate image coordinate after establishing mathematical coordinates when rotating again and rotating
Relationship is defined as the coordinate transform of number-figure；Assuming that coordinate system where rotated image is new images coordinate system, W2And H2For new images
Height and width, mathematical coordinates system origin (0,0) is new images coordinate system midpoint (0.5W after rotation when rotation2,0.5H2), it is new to scheme
As coordinate mooring pointsWith mathematical coordinates mooring pointsMapping relations are as follows:
(4) pixel assignment: after above-mentioned figure-number coordinate transform, coordinate rotation and the coordinate transform of number-figure, motor vehicle after rotation
The coordinate of number plate imagePreceding coordinate (i, j) mapping relations are as follows with rotating:
Assuming that image is I4 after automotive number plate image rotation, when formula (12)WithWhen being simultaneously integer, pixel assignment is such as
Under:
When formula (12)OrWhen not being integer, since image coordinate is integer,It is then non-image coordinate, before rotation
Pixel value at coordinate (i, j)It cannot be mapped as pixel value after rotating
When each coordinate of rotated image I4When mapping can be established with original image I1 coordinate (i, j),
When rotated image I4 coordinateWhen mapping can not be established with original image I1 coordinate (i, j), pixel value at the coordinate
For null point.
9. the automotive number plate image inclination angle antidote rotated as claimed in claim 8 based on least square method and coordinate,
It is characterized in that,
Step 7 specifically includes:
(1) figure-mathematical coordinates transformation: with step 6 (3) on the contrary, establishingWithMapping relations:
(2) coordinate rotate: with step 6 (2) on the contrary,θ is rotated clockwise around origin (0,0), rotation recoil is designated asIt establishesWithMapping relations are as follows:
(3) number-figure coordinate transform: with step 6 (1) on the contrary, establishingWith (i, j) mapping relations:
(4) picture element interpolation: after above-mentioned figure-number coordinate transform, coordinate rotation and the coordinate transform of number-figure, motor vehicle after rotation
Coordinate (i, j) and coordinate after rotation before the rotation of number plate imageIt is as follows with mapping relations:
Similar with step 6, when the i or j of formula (17) are not integer, (i, j) is then non-image coordinate, it is assumed thatFor the upper left nearest with (i, j), upper right, lower-left, the pixel of bottom right 4,WithRow distance
For c, column distance d, estimated with bilinear interpolation methodIt is worth as follows:
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