CN104184958B - A kind of automatic exposure control method and its device based on FPGA suitable for space exploration imaging - Google Patents
A kind of automatic exposure control method and its device based on FPGA suitable for space exploration imaging Download PDFInfo
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Abstract
The present invention relates to a kind of automatic exposure control method and its device based on FPGA suitable for space exploration imaging, the method obtains current frame image mean flow rate by present frame subject image mean flow rate, time for exposure is chosen come self adaptation with the positive and negative and size of the difference of expected mean picture brightness according to current frame image mean flow rate, current frame image mean flow rate is reached expected mean picture brightness using the continuous loop iteration of successive frame.A kind of automatic exposure control device to implement above-mentioned automatic exposure control method includes optical lens, APS sensors, spectrum assignment FPGA.The present invention solves that target image in existing space detection imaging technology is over-exposed, technical problem that is weighing between target image segmentation and automatic exposure speed and stability, improve the contrast of image, can realize being carried out under various space exploration photoenvironments more rapidly, more stable, more accurately auto-exposure control, increased adaptive ability when space exploration environment is imaged.
Description
Technical field
The present invention relates to the auto-exposure control field in survey of deep space technology, particularly it is a kind of be applied to space exploration into
The automatic exposure control method and its device based on FPGA of picture.
Background technology
Influence of the auto-exposure control of imaging device to output image quality is very big.The target of auto-exposure control is
The image dark portion details of shooting main body is set not lose, highlights not overexposure, while mean flow rate is adapted to human eye viewing.
When being applied to the imaging device operation on orbit of space exploration, time for exposure whether suitable extremely important, the time for exposure
It is too short that scenery can be caused very dark, and it is long can cause scene brightness saturation, therefore it is required to carry out auto-exposure control, but
Auto-exposure control is extremely complex, and spectrum assignment is bad may to be absorbed in time for exposure disorder, dark situation when bright when occurring.Cause
Whether this auto-exposure control suitable, to imaging device it is critical that, be related to the success or failure of task.
Current civil camera comparative maturity in Control Technique for Automatic Exposure, can set according to night scene, daytime, portrait etc.
Required different exposure control modes, effect is fine, it is also possible to use aperture priority formula, shutter according to different shooting main bodys
Prerequisite formula and program mode auto-exposure control obtain Correct exposure.If the Control Technique for Automatic Exposure of civil camera is applied to
The space industries such as space exploration, there is limitation.
First from for automatic exposure control method, the imaging device of space exploration is 1. applied to, is carried out to shooting main body
During imaging, illumination condition, position, the shared image area size of main body are shot because of situations such as that cannot predict, it is impossible to according to existing
Field scene setting automatic exposure control mode.If the imaging device for being 2. applied to space exploration is integrally bright using existing image
Degree controls exposure, if the luminance difference shot between main body and background is too big, can cause to shoot main body occur it is under-exposed or
The over-exposed phenomenon of person.If being 3. applied to the imaging device of space exploration using the reference brightness value controlling party of civil camera
Method, by image block, the brightness of each piece of subgraph is used to set up with reference to brightness value, and the reference brightness value can be by adjustment
Aperture size is obtained, and equally can also obtain the reference brightness value by setting shutter speed certainly, then be applied to space exploration
Imaging device is unattended, it is impossible to set aperture or shutter.4. civil camera have by studying under different illumination conditions
Relation between brightness and exposure value is exposed control, the imaging device of application space detection cannot carry out in advance brightness with
Demarcation between exposure value, so such exposal control method can not be used.5. civilian automatic exposure control method is base
Auto-exposure control is carried out in entire image, when main body is shot with respect to background very little, shooting main body can be caused over-exposed.
When shooting main body is very bright, background is dark, should now reduce the time for exposure；But due to calculating entire image,
The brightness number of pixels high number of pixels low much smaller than brightness, therefore entire image is dark, in order to improve the bright of entire image
Degree, continues to increase the time for exposure, ultimately results in shooting main body over-exposed.Therefore need to divide in existing automatic exposure algorithm
Shooting subject image is cut out, effective auto-exposure control is carried out to shooting subject image.6. it is existing to shooting subject image
Automatic exposure algorithm, in order to be partitioned into shooting subject image, split through frequently with constant brightness threshold value, but due to application
Influenceed in the temperature of space exploration imaging device, constant brightness Threshold segmentation does not adapt to various situations, it is therefore desirable to will be adaptive
The method of Threshold segmentation is answered to be introduced into automatic exposure control method.
Secondly from for the selection of automatic exposure step-length, the step-length of automatic exposure search can influence search speed and search stabilization
Trade-off relationship between property.Time for exposure adjusting step is too small to increase searching times, cause to reduce search speed；And if exposed
Light time adjusting step is long to be likely to result in search cannot restrain, and be vacillated now to the left, now to the right unstable phenomenon in optimum exposure point.It is existing
Automatic explosion method majority step-size in search can not dynamically be adjusted according to the brightness case of different scenes.
Finally from for the device for realizing automatic exposure control method, the particular microprocessor part that civil camera is typically used
To realize automatic exposure control method, and such particular microprocessor part can not typically apply space product, it is impossible in deep space
Ensure the reliability of space borne imagery device under environment.Thus automatic exposure will be realized using the device for being adapted to space exploration environment
Light control method, and automatic exposure control method is optimized.
At present, the method for space optical remote camera adjustments exposure is simultaneously few, and large-scale remote sensing of the earth camera is because its ground
The certainty of target, it is possible to use when spoke Luminance Analysis software, camera opticses and sensor chip characteristic draw accurate exposure
Between, need to only be switched over according to several grades of time for exposure of the different set of ground scenery.
The domestic space exploration imaging device automatic exposure control method that is applied at present is because imaging device cannot be to shooting
Main body is identified, when scenery is relative complex in visual field, it is impossible to carry out effective spectrum assignment, dry by noise and non-shooting main body
Disturb big so that main body brightness is shot in image and is difficult in a suitable scope, increase the difficulty of auto-exposure control.
The content of the invention
In view of this, it is a primary object of the present invention to provide it is a kind of suitable for space exploration imaging based on FPGA from
Dynamic exposal control method and its device.
In order to achieve the above object, the technical proposal of the invention is realized in this way：
The invention provides a kind of automatic exposure control method based on FPGA suitable for space exploration imaging, to current
Two field picture uses adaptive threshold fuzziness, identifies present frame subject image, is worked as by present frame subject image mean flow rate
Prior image frame mean flow rate, selects with the size of the difference of expected mean picture brightness according to current frame image mean flow rate come self adaptation
The time for exposure is taken, current frame image mean flow rate is reached expected mean picture brightness using the continuous loop iteration of successive frame, its
In, auto-exposure control step is：
Step (11)：The mean picture brightness of present frame is calculated, with the half of the average of all pixels of current frame image
Used as adaptive threshold, the pixel that will be greater than being equal to threshold value is divided into present frame subject image, then present frame subject image is bright
Degree carries out the cumulative mean picture brightness for being averaging and obtaining present frame, comprises the following steps：
Step (111)：The color composograph brightness of RGB tri-, will using rgb color space to YUV colour space transformations relation
Pixel is adjacent four components R of entire image of M × N, G1, G2, B weighted average obtain an image brightness data, by M
× N number of value of color is converted to M/2 × N/2 brightness value.
Step (112)：Brightness of image sampling is extracted, and the M/2 × N/2 brightness value that the colors of RGB tri- synthesize is pressed in column direction
According to the sampling principle of 1/m, M/2 × N/2 brightness value is converted into M/2m × N/2 brightness value.
Step (113)：Image line mean flow rate is calculated, M/2m × N/2 every a line all pixels of brightness value of calculating
Average value, and threshold value will be more than or equal to as the adaptive threshold of current line using the half of the average value of previous row in current line
Pixel be divided into current line subject image, then the brightness of current line subject image is carried out into the cumulative figure for being averaging and obtaining current line
As mean flow rate, M/2m × N/2 brightness value is converted into N/2 row average brightness.
Step (114)：Image block mean flow rate is calculated, M/2m × N/2 brightness value is synthesized 1 piece with adjacent n rows,
M/2m × N/2 brightness values are divided into N/2n blocks, the average value of adjacent n rows is added up to be averaging obtains each piece average bright
Degree, obtains N/2n Block Brightness average value.
Step (115)：Mean picture brightness is calculated, N/2n average brightness is added up to be averaging obtains entire image
Luminance mean value, using the half of average as adaptive threshold, the pixel that will be greater than being equal to threshold value is divided into present frame subject image,
The brightness of present frame subject image is carried out into the cumulative mean picture brightness Y (mean) for being averaging and obtaining present frame again.
Step (12)：The mean picture brightness of present frame compares with expected mean picture brightness, if the image of present frame
Mean flow rate is less than or equal to setting mean picture brightness difference Y (th) with the absolute value of the difference of expected mean picture brightness, just
Think that auto-exposure control has controlled to stop the adjustment of time for exposure in place, using the time for exposure of present frame as next frame
Time for exposure, if the mean picture brightness of present frame is schemed with the absolute value of the difference of expected mean picture brightness more than setting
As mean flow rate difference Y (th), then enter time for exposure adjustment.
Step (13)：Determine the next frame time for exposure, the determination of next frame automatic exposure time is the exposure in present frame
On the basis of time, the mean picture brightness according to present frame is entered with the positive and negative and size of the difference of expected mean picture brightness
The row time for exposure selects, and comprises the following steps：
Step (131)：If the mean picture brightness of present frame is just next frame with the difference of expected mean picture brightness
Image exposuring time is accomplished by reducing the time for exposure on the basis of the previous frame image time for exposure；
Step (132)：If the mean picture brightness of present frame is negative, next frame with the difference of expected mean picture brightness
Image exposuring time is accomplished by increasing the time for exposure on the basis of the previous frame image time for exposure；
Step (133)：It is true that the mean picture brightness of present frame carrys out self adaptation with the size of the difference of expected mean picture brightness
Fixed to increase, reduce exposure time values, the exposure time values for increase, reducing are worked as step-length numerical value R × luminance difference × time for exposure
Value t；
Step (134)：Next frame image exposuring time is reduced, if the time for exposure of former frame and exposure time range
Lower limit difference more than the exposure time values for determining to reduce, then the time for exposure of next frame subtract determination for time for exposure of former frame
Reduction exposure time values；Otherwise directly using the lower limit of exposure time range as next frame time for exposure；
Step (135)：Next frame image exposuring time increases, if the time for exposure of former frame and exposure time range
More than the increased exposure time values for determining, then the time for exposure of next frame is the time for exposure of former frame plus true to upper limit difference
Fixed increased exposure time values；Otherwise directly using the higher limit of exposure time range as next frame time for exposure；
In such scheme, the rgb color space to YUV colour space transformations relation is (8R+R+4B+16G1+2G2+
G2)/32, wherein：
G1 is the G components of strange passage；
G2 is the G components of even passage；
In such scheme, described automatic exposure control method runs in spectrum assignment FPGA, wherein, spectrum assignment
FPGA is the A54SX72A-CQ208B of anti-molten formula FPGA, its model Actel companies of space flight level.
In such scheme, the time for exposure gear of described automatic exposure control method is divided into two grades, a grades of time for exposure
Scope is 4 μ s~140ms, and b grades of exposure time range is 16 μ s~560ms.
A kind of automatic exposure control device based on FPGA suitable for space exploration imaging, the automatic exposure control device
Including optical lens, APS sensors, spectrum assignment FPGA；Wherein, optical lens, APS sensors, spectrum assignment FPGA be successively
Place,
Optical lens, for by target imaging to be imaged in APS sensors；
APS sensors, for converting optical signals into electronic signal；
Spectrum assignment FPGA, calculates, and gained brightness of image is compared with expected brightness of image for brightness of image
Compared with determining the automatic exposure time.
Advantage for present invention：
1st, the present invention can be realized under various illumination conditions, temperature conditions, the adaptivenon-uniform sampling to shooting subject image,
Shooting subject image to being partitioned into carries out effective spectrum assignment.
2nd, adaptive threshold is introduced into automatic exposure control method by the present invention, it is possible to achieve oneself under various temperature regimes
Dynamic spectrum assignment.
3rd, in the present invention automatic exposure time adjustment by shooting image mean flow rate and expected mean picture brightness difference
Value size determines that brightness of image difference is smaller, and the time for exposure of adjustment is smaller, and brightness of image difference is bigger, during the exposure of adjustment
Between it is bigger.Such auto-exposure control mechanism ensure that the time for exposure adjustment with depth of exposure change, reach search speed and
Balance between search stability.
4th, the present invention can fast and accurately adjust exposure value, and regulation exposure value is more stable, it is possible to prevente effectively from due to
The explosure flash phenomenon for causing is not restrained.
5th, the present invention uses automatic exposure control method, not true to the bright target of dark background in space exploration, target sizes
The various situations such as fixed obtain good exposure effect, and convergence is fine.
6th, the present invention realizes automatic exposure control method using the anti-molten formula FPGA of space flight level, adapts to space exploration imaging
Space environment, improves the reliability of automatic exposure device.
Brief description of the drawings
Fig. 1 is automatic exposure control method block diagram of the invention；
Fig. 2 is that brightness of image of the invention calculates block diagram；
Fig. 3 is time for exposure selection block diagram of the invention；
Fig. 4 is automatic exposure control device schematic diagram of the invention；
Marked in its figure：21- optical lens, 22-APS sensors, 23- spectrum assignments FPGA；
Fig. 5 is auto-exposure control flow chart of the invention；
Marked in its figure：Y (mean)-current frame image mean flow rate, Y (ref)-expection mean picture brightness, Y
(th)-setting mean picture brightness difference.
Specific embodiment
Below in conjunction with the accompanying drawings and specific embodiment the present invention is further described in more detail, but this should not be limited with this
The protection domain of invention.
The invention provides it is a kind of suitable for space exploration imaging the automatic exposure control method based on FPGA, it is described from
Dynamic exposal control method uses adaptive threshold fuzziness to current frame image, present frame subject image is identified, by present frame master
Body mean picture brightness obtains current frame image mean flow rate, according to current frame image mean flow rate and expected mean picture brightness
Size of the difference come self adaptation choose the time for exposure, reach current frame image mean flow rate using the continuous loop iteration of successive frame
Expected mean picture brightness, as shown in figure 1, wherein, automatic exposure control method step is：
Step (11)：The mean picture brightness of present frame is calculated, with the half of the average of all pixels of current frame image
Used as adaptive threshold, the pixel that will be greater than being equal to threshold value is divided into present frame subject image, then present frame subject image is bright
Degree carries out the cumulative mean picture brightness for being averaging and obtaining present frame, as shown in Fig. 2 comprising the following steps：
Step (111)：The color composograph brightness of RGB tri-, will using rgb color space to YUV colour space transformations relation
Pixel is adjacent four components R of entire image of M × N, G1, G2, B weighted average obtain an image brightness data, by M
× N number of value of color is converted to M/2 × N/2 brightness value, for example, 2352 × 1728 value of colors are converted into 1176 × 864 brightness
Value.
Step (112)：Brightness of image sampling is extracted, and the M/2 × N/2 brightness value that the colors of RGB tri- synthesize is pressed in column direction
According to the sampling principle of 1/m, M/2 × N/2 brightness value is converted into M/2m × N/2 brightness value, such as in column direction according to 1/8
Sampling principle, 1176 × 864 brightness values are converted into 147 × 864 brightness values.
Step (113)：Image line mean flow rate is calculated, M/2m × N/2 every a line all pixels of brightness value of calculating
Average value, and threshold value will be more than or equal to as the adaptive threshold of current line using the half of the average value of previous row in current line
Pixel be divided into current line subject image, then the brightness of current line subject image is carried out into the cumulative figure for being averaging and obtaining current line
As mean flow rate, M/2m × N/2 brightness value is converted into N/2 row average brightness.
Step (114)：Image block mean flow rate is calculated, M/2m × N/2 brightness value is synthesized 1 piece with adjacent n rows,
M/2m × N/2 brightness values are divided into N/2n blocks, the average value of adjacent n rows is added up to be averaging obtains each piece average bright
Degree, obtains N/2n Block Brightness average value, and such as 147 × 864 brightness values synthesize 1 piece with 27 adjacent rows, by 147 ×
864 brightness values are divided into 32 pieces.
Step (115)：Mean picture brightness is calculated, N/2n average brightness is added up to be averaging obtains entire image
Luminance mean value, using the half of average as adaptive threshold, the pixel that will be greater than being equal to threshold value is divided into present frame subject image,
The brightness of present frame subject image is carried out into the cumulative mean picture brightness for being averaging and obtaining present frame again.
Step (12)：The mean picture brightness of present frame compares with expected mean picture brightness, if the image of present frame
Mean flow rate is less than or equal to setting mean picture brightness difference Y (th) with the absolute value of the difference of expected mean picture brightness, just
Think that auto-exposure control has controlled to stop the adjustment of time for exposure in place, using the time for exposure of present frame as next frame
Time for exposure, if the brightness of image of present frame is bright more than setting image averaging with the absolute value of the difference of expected brightness of image
Degree difference Y (th), then enter time for exposure adjustment, such as Y (th)=8.
Step (13)：Determine the next frame time for exposure, the determination of next frame automatic exposure time is the exposure in present frame
On the basis of time, the mean picture brightness according to present frame is entered with the positive and negative and size of the difference of expected mean picture brightness
The row time for exposure selects, as shown in figure 3, comprising the following steps：
Step (131)：If the difference of the mean picture brightness of present frame and expected mean picture brightness is just, next
The two field picture time for exposure is accomplished by reducing the time for exposure on the basis of the previous frame image time for exposure；
Step (132)：If the mean picture brightness of present frame is negative with the difference of expected mean picture brightness, next
The two field picture time for exposure is accomplished by increasing the time for exposure on the basis of the previous frame image time for exposure；
Step (133)：The mean picture brightness of present frame carries out self adaptation with the size of the difference of expected mean picture brightness
The selection of the time for exposure for increase, reducing, the exposure time values for increase, reducing are time for exposure step-length numerical value R × luminance difference
× time for exposure equivalent value t, such as time for exposure step-length numerical value and time for exposure equivalent value are as shown in table 1.
Table 1 is automatic exposure control parameter table of the invention
Step (134)：Next frame image exposuring time is reduced, if the time for exposure of former frame and exposure time range
Lower limit difference more than the reduction for determining exposure time values, then the time for exposure of next frame subtract really for time for exposure of former frame
The exposure time values of fixed reduction；Otherwise directly using the lower limit of exposure time range as next frame time for exposure, for example
Exposure time range is as shown in table 1.
Step (135)：Next frame image exposuring time increases, if the time for exposure of former frame and exposure time range
More than the increased exposure time values for determining, then the time for exposure of next frame is the time for exposure of former frame plus true to upper limit difference
Fixed increased exposure time values；Otherwise directly using the range higher limit of time for exposure as next frame time for exposure, for example
Exposure time range is as shown in table 1.
The rgb color space to YUV colour space transformations relation be (8R+R+4B+16G1+2G2+G2)/32, wherein：
G1 is the G components of strange passage；
G2 is the G components of even passage；
Described automatic exposure control method runs in spectrum assignment FPGA, wherein, spectrum assignment FPGA is space flight level
The A54SX72A-CQ208B of anti-molten formula FPGA, its model Actel companies.
The time for exposure gear of described automatic exposure control method is divided into two grades, a grades of exposure time range for 4 μ s~
140ms, b grade of exposure time range is 16 μ s~560ms.
As shown in figure 4, the automatic exposure control device that a kind of Threshold segmentation and time for exposure based on FPGA are chosen, should be certainly
Dynamic exposure-control device includes optical lens, APS sensors, spectrum assignment FPGA；Wherein, optical lens, APS sensors, exposure
Photocontrol FPGA is sequentially placed；
Optical lens, for such as in APS sensors, the optical parametric of optical lens is ripple by target imaging to be imaged
Segment limit is 420~700nm, and visual field is 22.9 ° × 16.9 °, and focal length is 43mm, and F numbers are 8, and normal imaging distance is 5m~∞,
Transmission function MTF is more than 0.45；
APS sensors, for converting optical signals into electronic signal, the model IA-G3 of such as APS sensors, as
First quantity is 2352 × 1728, and pixel dimension is 7.4 μm of 7.4 μ m；
Spectrum assignment FPGA, calculates, and gained brightness of image is compared with expected brightness of image for brightness of image
Compared with determining automatic exposure time, such as A54SX72A-CQ208B of FPGA models Actel companies.
The auto-exposure control stream of the automatic exposure control device that the Threshold segmentation for being based on FPGA and time for exposure are chosen
Journey is as shown in figure 5, auto-exposure control flow makes gained brightness of image reach expected figure using the continuous loop iteration of successive frame
The process of image brightness.The first step, carries out current frame window mean flow rate and calculates；Second step, carries out brightness of image error judgment, such as
Fruit present image average brightness value Y (mean) is less than setting image with the absolute value of the difference of expected image brightness values Y (ref)
Mean flow rate difference Y (th), then it is assumed that the time for exposure is adjusted in place, stops the adjustment time for exposure, should by the time for exposure of this frame
Use next frame image exposure；3rd step, in brightness of image error judgment, if present image average brightness value Y (mean)
Enter more than mean picture brightness difference Y (th) is set, then with the absolute value of the difference of expected image brightness values Y (ref) and expose
Light time plus-minus step-length judges；4th step, automatic exposure time step is selected according to mean picture brightness size of the difference, such as
The mean picture brightness Y (mean) of fruit present frame is negative, then next two field picture with the difference of expected mean picture brightness Y (ref)
Time for exposure is accomplished by increasing the time for exposure on the basis of the previous frame image time for exposure, and increased exposure time values are exposure
Time step numerical value R × luminance difference × time for exposure equivalent value t.If the time for exposure of former frame and exposure time range
More than the increased exposure time values for determining, then the time for exposure of next frame is the time for exposure of former frame plus true to upper limit difference
Fixed increased exposure time values；Otherwise directly using the range higher limit of time for exposure as next frame time for exposure；5th
Step, if the mean picture brightness Y (mean) of present frame is just next frame with the difference of expected mean picture brightness Y (ref)
Image exposuring time is accomplished by reducing the time for exposure on the basis of the previous frame image time for exposure, and the exposure time values of reduction are
Time for exposure step-length numerical value R × luminance difference × time for exposure equivalent value t.If the time for exposure of former frame and time for exposure model
The lower limit difference enclosed more than the reduction for determining exposure time values, then the time for exposure of next frame subtract for time for exposure of former frame
Go the exposure time values of the reduction of determination；Otherwise directly using the lower limit of exposure time range as next frame time for exposure.
Claims (2)
1. it is a kind of suitable for space exploration imaging the automatic exposure control method based on FPGA, it is characterised in that：To present frame
Image uses adaptive threshold fuzziness, identifies present frame subject image, is obtained currently by present frame subject image mean flow rate
Two field picture mean flow rate, comes from according to current frame image mean flow rate with the positive and negative and size of the difference of expected mean picture brightness
Adapt to choose the time for exposure for determining next frame, reach current frame image mean flow rate using the continuous loop iteration of successive frame pre-
Phase mean picture brightness, wherein, auto-exposure control step is：
Step (11)：Calculate present frame mean picture brightness, using the half of the average of all pixels of current frame image as
Adaptive threshold, the pixel that will be greater than being equal to threshold value is divided into present frame subject image, then present frame subject image brightness is entered
Cumulative being averaging of row obtains current frame image mean flow rate, comprises the following steps：
Step (111)：The color composograph brightness of RGB tri-, using rgb color space to YUV colour space transformations relation by pixel
For adjacent four components R of the entire image of M × N, G1, G2, B weighted average obtain an image brightness data, by M × N
Individual value of color is converted to M/2 × N/2 brightness value；
Step (112)：Brightness of image sampling extract, by the color of R, G, B tri- synthesize M/2 × N/2 brightness value column direction according to
The sampling principle of 1/m, M/2m × N/2 brightness value is converted to by M/2 × N/2 brightness value；
Step (113)：Image line mean flow rate is calculated, the average of M/2m × N/2 every a line all pixels of brightness value is calculated
Value, and using the half of the average value of previous row as the adaptive threshold of current line, by the picture in current line more than or equal to threshold value
Element is divided into current line subject image, then the brightness of current line subject image is carried out into cumulative being averaging obtains the image of current line and put down
Equal brightness, N/2 row average brightness is converted to by M/2m × N/2 brightness value；
Step (114)：Image block mean flow rate is calculated, M/2m × N/2 brightness value 1 piece is synthesized with adjacent n rows, by M/
2m × N/2 brightness values are divided into N/2n blocks, and the average value of adjacent n rows is added up the mean flow rate for being averaging and obtaining each piece, is obtained
To N/2n Block Brightness average value；
Step (115)：Mean picture brightness is calculated, N/2n average brightness is added up and is averaging the brightness for obtaining entire image
Average, using the half of average as adaptive threshold, the pixel that will be greater than being equal to threshold value is divided into present frame subject image, then will
The brightness of present frame subject image carries out the cumulative mean picture brightness Y (mean) for being averaging and obtaining present frame；
Step (12)：The mean picture brightness of present frame compares with expected mean picture brightness, if the image averaging of present frame
Brightness is less than or equal to setting mean picture brightness difference Y (th) with the absolute value of the difference of expected mean picture brightness, is considered as
Auto-exposure control has controlled to stop the adjustment of time for exposure in place, using the time for exposure of present frame as the exposure of next frame
The light time, if the mean picture brightness of present frame is put down with the absolute value of the difference of expected mean picture brightness more than setting image
Equal luminance difference Y (th), then enter time for exposure adjustment；
Step (13)：Determine the next frame time for exposure, the determination of next frame automatic exposure time is the time for exposure in present frame
On the basis of, the mean picture brightness according to present frame is exposed with the positive and negative and size of the difference of expected mean picture brightness
Light selection of time, comprises the following steps：
Step (131)：If the mean picture brightness of present frame is just next frame figure with the difference of expected mean picture brightness
As the time for exposure is accomplished by reducing the time for exposure on the basis of the previous frame image time for exposure；
Step (132)：If the mean picture brightness of present frame is negative, next frame figure with the difference of expected mean picture brightness
As the time for exposure is accomplished by increasing the time for exposure on the basis of the previous frame image time for exposure；
Step (133)：The mean picture brightness of present frame carrys out self adaptation and determines to increase with the size of the difference of expected mean picture brightness
Plus, reduce exposure time values, increase, reduce exposure time values be time for exposure step-length numerical value R × luminance difference × exposure
Time equivalent value t；
Step (134)：Next frame image exposuring time is reduced, if the lower limit of the time for exposure of former frame and exposure time range
Difference more than the reduction for determining exposure time values, then the time for exposure of next frame subtract determination for time for exposure of former frame
The exposure time values of reduction；Otherwise directly using the lower limit of exposure time range as next frame time for exposure；
Step (135)：Next frame image exposuring time increases, if the upper limit of the time for exposure of former frame and exposure time range
More than the increased exposure time values for determining, then the time for exposure of next frame is the time for exposure of former frame plus determination to difference
Increased exposure time values；Otherwise directly using the higher limit of exposure time range as next frame time for exposure；
The rgb color space to YUV colour space transformations relation be (8R+R+4B+16G1+2G2+G2)/32, wherein：
G1 is the G components of strange passage；
G2 is the G components of even passage；
Described automatic exposure control method runs in spectrum assignment FPGA, wherein, spectrum assignment FPGA is anti-molten space flight level
The A54SX72A-CQ208B of formula FPGA, its model Actel company；
The time for exposure gear of described automatic exposure control method is divided into two grades, a grades of exposure time range for 4 μ s~
140ms, b grade of exposure time range is 16 μ s~560ms；
The automatic exposure control method based on FPGA for being applied to space exploration imaging can be realized in various illumination conditions, temperature
In the case of degree, the adaptivenon-uniform sampling to shooting subject image, the shooting subject image to being partitioned into carries out effective spectrum assignment；
Adaptive threshold is introduced automatic exposure by the automatic exposure control method based on FPGA for being applied to space exploration imaging
In control method, it is possible to achieve the auto-exposure control under various temperature regimes；
The adjustment of the automatic exposure time suitable for the automatic exposure control method based on FPGA of space exploration imaging is by clapping
Take the photograph mean picture brightness and determine that brightness of image difference is smaller, during the exposure of adjustment with the size of the difference of expected mean picture brightness
Between it is smaller, brightness of image difference is bigger, and the time for exposure of adjustment is bigger, when such auto-exposure control mechanism ensure that exposure
Between adjust with depth of exposure change, reach search speed and search stability between balance；
The automatic exposure control method based on FPGA for being applied to space exploration imaging can fast and accurately adjust exposure
Value, regulation exposure value is more stable, it is possible to prevente effectively from due to not restraining the explosure flash phenomenon for causing；
The automatic exposure control method based on FPGA for being applied to space exploration imaging uses automatic exposure control method, to sky
Between detect in the bright target of dark background, target sizes uncertain condition obtain good exposure effect, convergence is fine；
The automatic exposure control method based on FPGA for being applied to space exploration imaging instead melts formula FPGA come real using space flight level
Existing automatic exposure control method, adapts to space exploration imaging space environment, improves the reliability of automatic exposure device.
2. a kind of automatic exposure control device to realize automatic exposure control method described in claim 1, it is characterised in that should
Automatic exposure control device includes optical lens (21), APS sensors (22), spectrum assignment FPGA (23)；Wherein, optical lens
(21), APS sensors (22), spectrum assignment FPGA (23) are sequentially placed,
Optical lens (21), for by target imaging to be imaged in APS sensors (22)；
APS sensors (22), for converting optical signals into electronic signal；
Spectrum assignment FPGA (23), calculates, and gained brightness of image is compared with expected brightness of image for brightness of image
Compared with determining the automatic exposure time.
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