CN104184958A - Automatic exposure control method and device based on FPGA and suitable for space exploration imaging - Google Patents
Automatic exposure control method and device based on FPGA and suitable for space exploration imaging Download PDFInfo
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Abstract
The invention relates to an automatic exposure control method and device based on an FPGA and suitable for space exploration imaging. The method includes the steps that the current-frame image average brightness is acquired through the main current-frame image average brightness, time of exposure is adaptively selected according to whether a difference value between the current-frame image average brightness and the expected image average brightness is positive or negative and is large or small, continuous frames are adopted for continuous loop iteration, and therefore the current-frame image average brightness reaches the expected image average brightness. The automatic exposure control device for conducting the automatic exposure control method comprises an optical lens, an APS sensor and the exposure control FPGA. According to the method and device, the technical problems existing in excessive exposure of a target image, segmentation of the target image and balance between the automatic exposure speed and stability in the existing space exploration imaging technology are solved, the image contrast ratio is increased, faster, more stable and more accurate automatic exposure control can be conducted in various space exploration light environments, and adaptive ability in the space exploration environment imaging process is improved.
Description
Technical field
The present invention relates to the auto-exposure control field in survey of deep space technology, particularly a kind of automatic exposure control method based on FPGA and device thereof that is applicable to space exploration imaging.
Background technology
The auto-exposure control of imaging device is very large on the impact of output image quality.The target of auto-exposure control is that the dark portion of the image details of the shooting body is not lost, and highlights is overexposure not, and the applicable human eye of mean flow rate is watched simultaneously.
While being applied to the imaging device operation on orbit of space exploration, whether the time for exposure is suitable extremely important, too short meeting of time for exposure causes scenery very dark, and the long scenery luminance saturation that can cause, therefore it is essential carrying out auto-exposure control, but auto-exposure control is very complicated, exposure is controlled badly may be absorbed in time for exposure disorder, dark situation when bright while appearance.Therefore whether auto-exposure control is suitable, is vital to imaging device, is related to the success or failure of task.
Civil camera comparative maturity in Control Technique for Automatic Exposure at present, can set needed different exposure control modes according to night scene, daytime, portrait etc., effect is fine, also can adopt aperture priority formula, ShutterPriority Auto formula and program mode auto-exposure control to obtain accurate exposure according to different the shooting bodies.If the Control Technique for Automatic Exposure of civil camera is applied to the space industries such as space exploration, just have limitation.
First from automatic exposure control method, 1. be applied to the imaging device of space exploration, when the shooting body is carried out to imaging, owing to cannot predicting the situations such as the illumination condition, position, shared image area size of the shooting body, cannot set automatic exposure control mode according to scene.Adopt existing integral image brightness to control exposure if be 2. applied to the imaging device of space exploration, if the luminance difference between the shooting body and background is too large, can make the shooting body occur under-exposed or over-exposed phenomenon.If be 3. applied to space exploration imaging device adopt civil camera with reference to brightness value control method, by image block, the brightness of each piece subimage is used to arrange with reference to brightness value, this can obtain by adjusting aperture size with reference to brightness value, certainly equally also can obtain this with reference to brightness value by shutter speed is set, it is unattended being applied to space exploration imaging device, cannot set aperture or shutter.The control that exposes of brightness under research different illumination conditions that what 4. civil camera had pass through and the relation between exposure value, the imaging device that application space is surveyed cannot carry out the demarcation between brightness and exposure value in advance, so can not adopt such exposal control method.5. civilian automatic exposure control method all carries out auto-exposure control based on entire image, in the time that the relative background of the shooting body is very little, can cause the shooting body over-exposed.When the shooting body is very bright, background is when darker, now should reduce the time for exposure; But due to entire image is calculated, the high number of pixels of brightness is much smaller than the low number of pixels of brightness, and therefore entire image is darker, in order to improve the brightness of entire image, continuing increases the time for exposure, finally causes the shooting body over-exposed.Therefore need in existing automatic exposure algorithm, be partitioned into the shooting body image, the shooting body image is carried out to effective auto-exposure control.6. the existing automatic exposure algorithm to the shooting body image, in order to be partitioned into the shooting body image, often adopt constant brightness threshold value to cut apart, but owing to being applied to the temperature impact of space exploration imaging device, constant brightness Threshold segmentation can not adapt to various situations, therefore needs the method that adaptive threshold is cut apart to introduce automatic exposure control method.
Secondly choose from automatic exposure step-length, the step-length of automatic exposure search can affect the balance relation between search speed and search stability.Time for exposure is adjusted the too small meeting of step-length increases searching times, causes reducing search speed; And if the time for exposure adjusts that step-length is long may cause search to restrain, in the optimum exposure point unsettled phenomenon of vacillating now to the left, now to the right.Existing automatic explosion method majority can not be adjusted step-size in search dynamically according to the brightness situation of different scenes.
Last from realizing the device of automatic exposure control method, the general particular microprocessor part adopting of civil camera is realized automatic exposure control method, and such particular microprocessor part generally can not be applied space product, can not under deep space environment, ensure the reliability of space borne imagery device.The device that employing is adapted to space exploration environment is thus realized automatic exposure control method, and automatic exposure control method is optimized.
At present, the method of space optical remote camera adjustments exposure is also few, large-scale remote sensing of the earth camera is because the certainty of its ground target, can use spoke Luminance Analysis software, camera optics and sensor chip characteristic to draw the accurate time for exposure, only need switch 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 to is at present because imaging device cannot be identified the shooting body, when in visual field when scenery relative complex, cannot carry out effectively exposure controls, disturbed by noise and non-the shooting body large, make the shooting body brightness in image be difficult to, in a suitable scope, increase the difficulty of auto-exposure control.
Summary of the invention
In view of this, main purpose of the present invention is to provide a kind of automatic exposure control method based on FPGA and device thereof that is applicable to space exploration imaging.
In order to achieve the above object, technical scheme of the present invention is achieved in that
The invention provides a kind of automatic exposure control method based on FPGA that is applicable to space exploration imaging, adopt adaptive threshold to cut apart to current frame image, identify present frame subject image, obtain current frame image mean flow rate by present frame subject image mean flow rate, carry out self adaptation according to current frame image mean flow rate with the difference size of expection mean picture brightness and choose the time for exposure, adopt the continuous loop iteration of successive frame to make current frame image mean flow rate reach expection mean picture brightness, wherein, auto-exposure control step is:
Step (11): the mean picture brightness of calculating present frame, using the half of the average of all pixels of current frame image as adaptive threshold, be present frame subject image by the pixel segmentation that is more than or equal to threshold value, again the brightness of present frame subject image is added up and is averaging the mean picture brightness that obtains present frame, comprise the following steps:
Step (111): RGB tri-look composograph brightness, adopt adjacent four components R, G1, G2, the B weighted average of the entire image that rgb color space is M × N to YUV colour space transformation relation by pixel to obtain image brightness data, M × N value of color is converted to M/2 × N/2 brightness value.
Step (112): image brightness sampling is extracted, by M/2 × N/2 RGB tri-looks synthetic brightness value at column direction according to the sampling principle of 1/m, M/2 × N/2 brightness value is converted to M/2m × N/2 brightness value.
Step (113): computed image row mean flow rate, calculate the mean value of all pixels of every a line of M/2m × N/2 brightness value, and adaptive threshold using the half of the mean value of previous row as current line, be current line subject image by the pixel segmentation that is more than or equal to threshold value in current line, again the brightness of current line subject image is added up and is averaging the mean picture brightness that obtains current line, M/2m × N/2 brightness value is converted to N/2 row average brightness.
Step (114): computed image piece mean flow rate, M/2m × N/2 brightness value synthesized to 1 so that adjacent n is capable, M/2m × N/2 brightness value is divided into N/2n piece, be averaging by cumulative mean value capable adjacent n the mean flow rate that obtains each piece, obtain N/2n Block Brightness mean value.
Step (115): computed image mean flow rate, by cumulative N/2n the average brightness brightness average that obtains entire image that is averaging, using the half of average as adaptive threshold, be present frame subject image by the pixel segmentation that is more than or equal to threshold value, then the brightness of present frame subject image is added up and is averaging the mean picture brightness Y (mean) that obtains present frame.
Step (12): the mean picture brightness of present frame and the comparison of expection mean picture brightness, if the mean picture brightness of present frame is less than or equal to and sets mean picture brightness difference Y (th) with the absolute value of the difference of expection mean picture brightness, just think that auto-exposure control controls and put in place, stop the adjustment of time for exposure, time for exposure using time for exposure of present frame as next frame, if the mean picture brightness of present frame is greater than and sets mean picture brightness difference Y (th) with the absolute value of the difference of expection mean picture brightness, enter time for exposure adjustment.
Step (13): determine the next frame time for exposure, next frame automatic exposure time definite is on the basis of the time for exposure of present frame, carry out time for exposure selection according to the mean picture brightness of present frame and the positive and negative and size of the difference of expection mean picture brightness, comprise the following steps:
Step (131): if the mean picture brightness of present frame with the difference of expection mean picture brightness for just, next frame image exposuring time just need to reduce the time for exposure on the basis of former frame image exposuring time;
Step (132): if the mean picture brightness of present frame is negative with the difference of expection mean picture brightness, next frame image exposuring time just need to increase the time for exposure on the basis of former frame image exposuring time;
Step (133): the mean picture brightness of present frame is carried out the definite increase of self adaptation, reduced exposure time values with the difference size of expection mean picture brightness, and the exposure time values that increases, reduces is step-length numerical value R × luminance difference × time for exposure equivalent value t;
Step (134): next frame image exposuring time reduces, determine if the lower limit difference of the time for exposure of former frame and time for exposure scope is greater than the exposure time values that reduces, the time for exposure of next frame is former frame time for exposure deducts definite exposure time values reducing; Otherwise the directly time for exposure using the lower limit of time for exposure scope as next frame;
Step (135): next frame image exposuring time increases, if the upper limit difference of the time for exposure of former frame and time for exposure scope is greater than the exposure time values of definite increase, time for exposure that is former frame time for exposure of next frame adds the exposure time values of definite increase; Otherwise the directly time for exposure using the higher limit of time for exposure scope as next frame;
In such scheme, it is (8R+R+4B+16G1+2G2+G2)/32 that described rgb color space closes to YUV colour space transformation, wherein:
G1 is the G component of strange passage;
G2 is the G component of even passage;
In such scheme, described automatic exposure control method moves in FPGA is controlled in exposure, and wherein, it is the anti-molten formula FPGA of space flight level that FPGA is controlled in exposure, and its model is the A54SX72A-CQ208B of Actel company.
In such scheme, the time for exposure gear of described automatic exposure control method is divided into two grades, and the time for exposure scope of a shelves is 4 μ s～140ms, and the time for exposure scope of b shelves is 16 μ s～560ms.
Be applicable to the automatic exposure control device based on FPGA of space exploration imaging, this automatic exposure control device comprises optical lens, APS transducer, exposure control FPGA; Wherein, optical lens, APS transducer, exposure are controlled FPGA and are placed successively,
Optical lens, for by target imaging to be imaged at APS transducer;
APS transducer, for converting optical signalling to electronic signal;
FPGA is controlled in exposure, calculates, and the image brightness of gained image brightness and expection is compared for image brightness, determines the automatic exposure time.
The present invention has advantages of:
1, the present invention can realize under various illumination conditions, temperature conditions, and the self adaptation of the shooting body image is cut apart, and the shooting body image being partitioned into is carried out to effectively exposure and control.
2, the present invention introduces adaptive threshold in automatic exposure control method, can realize the auto-exposure control under various temperature regimes.
3, in the present invention, the adjustment of automatic exposure time is determined by photographic images mean flow rate and the difference size of expection mean picture brightness, and image brightness difference is less, and the time for exposure of adjustment is less, and image brightness difference is larger, and the time for exposure of adjustment is larger.Such auto-exposure control mechanism the time for exposure adjust with depth of exposure and change, reach search speed and the balance of search between stability.
4, the present invention can adjust exposure value fast and accurately, regulates exposure value more stable, can effectively avoid the explosure flash phenomenon causing owing to not restraining.
5, the present invention adopts automatic exposure control method, and to the bright target of the dark background in space exploration, target sizes be uncertain etc., various situations obtain good exposure effect, and convergence is fine.
6, the present invention adopts the anti-molten formula FPGA of space flight level to realize automatic exposure control method, can adapt 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 present invention;
Fig. 2 is that image brightness of the present invention is calculated block diagram;
Fig. 3 selects block diagram the time for exposure of the present invention;
Fig. 4 is automatic exposure control device schematic diagram of the present invention;
In its figure, be labeled as: FPGA is controlled in 21-optical lens, 22-APS transducer, 23-exposure;
Fig. 5 is auto-exposure control flow chart of the present invention;
In its figure, be labeled as: Y (mean)-current frame image mean flow rate, Y (ref)-expection mean picture brightness, Y (th)-setting mean picture brightness difference.
Embodiment
Below in conjunction with drawings and the specific embodiments, the present invention is further described in more detail, but should not limit the scope of the invention with this.
The invention provides a kind of automatic exposure control method based on FPGA that is applicable to space exploration imaging, described automatic exposure control method adopts adaptive threshold to cut apart to current frame image, identify present frame subject image, obtain current frame image mean flow rate by present frame subject image mean flow rate, carry out self adaptation according to current frame image mean flow rate with the difference size of expection mean picture brightness and choose the time for exposure, adopt the continuous loop iteration of successive frame to make current frame image mean flow rate reach expection mean picture brightness, as shown in Figure 1, wherein, automatic exposure control method step is:
Step (11): the mean picture brightness of calculating present frame, using the half of the average of all pixels of current frame image as adaptive threshold, be present frame subject image by the pixel segmentation that is more than or equal to threshold value, again the brightness of present frame subject image is added up and is averaging the mean picture brightness that obtains present frame, as shown in Figure 2, comprise the following steps:
Step (111): RGB tri-look composograph brightness, adopt adjacent four components R, G1, G2, the B weighted average of the entire image that rgb color space is M × N to YUV colour space transformation relation by pixel to obtain image brightness data, M × N value of color is converted to M/2 × N/2 brightness value, for example, 2352 × 1728 value of colors is converted to 1176 × 864 brightness values.
Step (112): image brightness sampling is extracted, by M/2 × N/2 RGB tri-looks synthetic brightness value at column direction according to the sampling principle of 1/m, M/2 × N/2 brightness value is converted to M/2m × N/2 brightness value, for example at column direction according to 1/8 sampling principle, 1176 × 864 brightness values are converted to 147 × 864 brightness values.
Step (113): computed image row mean flow rate, calculate the mean value of all pixels of every a line of M/2m × N/2 brightness value, and adaptive threshold using the half of the mean value of previous row as current line, be current line subject image by the pixel segmentation that is more than or equal to threshold value in current line, again the brightness of current line subject image is added up and is averaging the mean picture brightness that obtains current line, M/2m × N/2 brightness value is converted to N/2 row average brightness.
Step (114): computed image piece mean flow rate, M/2m × N/2 brightness value synthesized to 1 so that adjacent n is capable, M/2m × N/2 brightness value is divided into N/2n piece, by the cumulative mean value capable adjacent n mean flow rate that obtains each piece that is averaging, obtain N/2n Block Brightness mean value, for example 147 × 864 brightness values synthesize 1 with 27 adjacent row, and 147 × 864 brightness values are divided into 32.
Step (115): computed image mean flow rate, by cumulative N/2n the average brightness brightness average that obtains entire image that is averaging, using the half of average as adaptive threshold, be present frame subject image by the pixel segmentation that is more than or equal to threshold value, then the brightness of present frame subject image is added up and is averaging the mean picture brightness that obtains present frame.
Step (12): the mean picture brightness of present frame and the comparison of expection mean picture brightness, if the mean picture brightness of present frame is less than or equal to and sets mean picture brightness difference Y (th) with the absolute value of the difference of expection mean picture brightness, just think that auto-exposure control controls and put in place, stop the adjustment of time for exposure, time for exposure using time for exposure of present frame as next frame, if the image brightness of present frame is greater than and sets mean picture brightness difference Y (th) with the absolute value of the difference of expection image brightness, enter time for exposure adjustment, for example Y (th)=8.
Step (13): determine the next frame time for exposure, next frame automatic exposure time definite is on the basis of the time for exposure of present frame, carry out time for exposure selection according to the mean picture brightness of present frame and the positive and negative and size of the difference of expection mean picture brightness, as shown in Figure 3, comprise the following steps:
Step (131): if the mean picture brightness of present frame with the difference of expection mean picture brightness for just, next frame image exposuring time just need to reduce the time for exposure on the basis of former frame image exposuring time;
Step (132): if the mean picture brightness of present frame is negative with the difference of expection mean picture brightness, next frame image exposuring time just need to increase the time for exposure on the basis of former frame image exposuring time;
Step (133): the mean picture brightness of present frame is carried out self adaptation increase with the difference size of expection mean picture brightness, the selection of time for exposure of reducing, the exposure time values increase, reducing is step-length numerical value time for exposure, equivalent value t R × luminance difference × time for exposure, and for example 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 present invention
Step (134): next frame image exposuring time reduces, if the lower limit difference of the time for exposure of former frame and time for exposure scope is greater than definite exposure time values reducing, the time for exposure of next frame is former frame time for exposure deducts definite exposure time values reducing; Otherwise the directly time for exposure using the lower limit of time for exposure scope as next frame, for example scope is as shown in table 1 the time for exposure.
Step (135): next frame image exposuring time increases, if the upper limit difference of the time for exposure of former frame and time for exposure scope is greater than the exposure time values of definite increase, time for exposure that is former frame time for exposure of next frame adds the exposure time values of definite increase; Otherwise the directly time for exposure using the range limit value of time for exposure as next frame, for example scope is as shown in table 1 the time for exposure.
It is (8R+R+4B+16G1+2G2+G2)/32 that described rgb color space closes to YUV colour space transformation, wherein:
G1 is the G component of strange passage;
G2 is the G component of even passage;
Described automatic exposure control method moves in FPGA is controlled in exposure, and wherein, it is the anti-molten formula FPGA of space flight level that FPGA is controlled in exposure, and its model is the A54SX72A-CQ208B of Actel company.
The time for exposure gear of described automatic exposure control method is divided into two grades, and the time for exposure scope of a shelves is 4 μ s～140ms, and the time for exposure scope of b shelves is 16 μ s～560ms.
As shown in Figure 4, the automatic exposure control device that a kind of Threshold segmentation based on FPGA and time for exposure are chosen, this automatic exposure control device comprises that optical lens, APS transducer, exposure control FPGA; Wherein, optical lens, APS transducer, exposure are controlled FPGA and are placed successively;
Optical lens, for by target imaging to be imaged at APS transducer, the optical parametric of for example optical lens is that wavelength band is 420～700nm, visual field is 22.9 ° × 16.9 °, and focal length is 43mm, and F number is 8, normal imaging distance is 5m～∞, and transfer function MTF is for being greater than 0.45;
APS transducer, for converting optical signalling to electronic signal, for example model of APS transducer is IA-G3, and pixel quantity is 2352 × 1728, and pixel dimension is 7.4 μ m × 7.4 μ m;
FPGA is controlled in exposure, calculates, and the image brightness of gained image brightness and expection is compared for image brightness, determines the automatic exposure time, and for example FPGA model is the A54SX72A-CQ208B of Actel company.
As shown in Figure 5, auto-exposure control flow process adopts the continuous loop iteration of successive frame to make gained image brightness reach the process of the image brightness of expection to the auto-exposure control flow process of the automatic exposure control device chosen of Threshold segmentation that should be based on FPGA and time for exposure.The first step, carries out present frame window mean flow rate and calculates; Second step, carry out image brightness error judgment, if present image average brightness value Y (mean) is less than and sets mean picture brightness difference Y (th) with the absolute value of the difference of the image brightness value Y (ref) of expection, think that the time for exposure adjusts to the right place, stop adjusting the time for exposure, the time for exposure of this frame is applied to next frame image exposure; The 3rd step, in image brightness error judgment, if present image average brightness value Y (mean) is greater than and sets mean picture brightness difference Y (th) with the absolute value of the difference of the image brightness value Y (ref) of expection, enter time for exposure plus-minus step-length judgement; The 4th step, automatic exposure time step is selected according to mean picture brightness difference size, if the mean picture brightness Y of present frame (mean) is negative with the difference of expection mean picture brightness Y (ref), next frame image exposuring time just need to increase the time for exposure on the basis of former frame image exposuring time, and the exposure time values of increase is step-length numerical value time for exposure, equivalent value t R × luminance difference × time for exposure.If the upper limit difference of the time for exposure of former frame and time for exposure scope is greater than the exposure time values of definite increase, time for exposure that is former frame time for exposure of next frame adds the exposure time values of definite increase; Otherwise the directly time for exposure using the range limit value of time for exposure as next frame; The 5th step, if the mean picture brightness Y of present frame (mean) with the difference of expection mean picture brightness Y (ref) for just, next frame image exposuring time just need to reduce the time for exposure on the basis of former frame image exposuring time, and the exposure time values reducing is step-length numerical value time for exposure, equivalent value t R × luminance difference × time for exposure.If the lower limit difference of the time for exposure of former frame and time for exposure scope is greater than definite exposure time values reducing, the time for exposure of next frame is former frame time for exposure deducts definite exposure time values reducing; Otherwise the directly time for exposure using the lower limit of time for exposure scope as next frame.
Claims (5)
1. one kind is applicable to the automatic exposure control method based on FPGA of space exploration imaging, it is characterized in that: adopt adaptive threshold to cut apart to current frame image, identify present frame subject image, obtain current frame image mean flow rate by present frame subject image mean flow rate, according to the difference of current frame image mean flow rate and expection mean picture brightness positive and negative and big or small come self adaptation choose time for exposure of definite next frame, adopt the continuous loop iteration of successive frame to make current frame image mean flow rate reach expection mean picture brightness, wherein, auto-exposure control step is:
Step (11): the mean picture brightness of calculating present frame, using the half of the average of all pixels of current frame image as adaptive threshold, be present frame subject image by the pixel segmentation that is more than or equal to threshold value, again the brightness of present frame subject image being added up to be averaging obtains current frame image mean flow rate, comprises the following steps:
Step (111): RGB tri-look composograph brightness, adopt adjacent four components R, G1, G2, the B weighted average of the entire image that rgb color space is M × N to YUV colour space transformation relation by pixel to obtain image brightness data, M × N value of color is converted to M/2 × N/2 brightness value;
Step (112): image brightness sampling is extracted, by M/2 × N/2 R, G, B tri-looks synthetic brightness value at column direction according to the sampling principle of 1/m, M/2 × N/2 brightness value is converted to M/2m × N/2 brightness value;
Step (113): computed image row mean flow rate, calculate the mean value of all pixels of every a line of M/2m × N/2 brightness value, and adaptive threshold using the half of the mean value of previous row as current line, be current line subject image by the pixel segmentation that is more than or equal to threshold value in current line, again the brightness of current line subject image is added up and is averaging the mean picture brightness that obtains current line, M/2m × N/2 brightness value is converted to N/2 row average brightness;
Step (114): computed image piece mean flow rate, M/2m × N/2 brightness value synthesized to 1 so that adjacent n is capable, M/2m × N/2 brightness value is divided into N/2n piece, be averaging by cumulative mean value capable adjacent n the mean flow rate that obtains each piece, obtain N/2n Block Brightness mean value;
Step (115): computed image mean flow rate, by cumulative N/2n the average brightness brightness average that obtains entire image that is averaging, using the half of average as adaptive threshold, be present frame subject image by the pixel segmentation that is more than or equal to threshold value, then the brightness of present frame subject image is added up and is averaging the mean picture brightness Y (mean) that obtains present frame;
Step (12): the mean picture brightness of present frame and the comparison of expection mean picture brightness, if the mean picture brightness of present frame is less than or equal to and sets mean picture brightness difference Y (th) with the absolute value of the difference of expection mean picture brightness, just think that auto-exposure control controls and put in place, stop the adjustment of time for exposure, time for exposure using time for exposure of present frame as next frame, if the mean picture brightness of present frame is greater than and sets mean picture brightness difference Y (th) with the absolute value of the difference of expection mean picture brightness, enter time for exposure adjustment,
Step (13): determine the next frame time for exposure, next frame automatic exposure time definite is on the basis of the time for exposure of present frame, carry out time for exposure selection according to the mean picture brightness of present frame and the positive and negative and size of the difference of expection mean picture brightness, comprise the following steps:
Step (131): if the mean picture brightness of present frame with the difference of expection mean picture brightness for just, next frame image exposuring time just need to reduce the time for exposure on the basis of former frame image exposuring time;
Step (132): if the mean picture brightness of present frame is negative with the difference of expection mean picture brightness, next frame image exposuring time just need to increase the time for exposure on the basis of former frame image exposuring time;
Step (133): the mean picture brightness of present frame is carried out self adaptation with the difference size of expection mean picture brightness and determined the exposure time values that increases, reduces, and the exposure time values that increases, reduces is step-length numerical value time for exposure, equivalent value t R × luminance difference × time for exposure;
Step (134): next frame image exposuring time reduces, if the lower limit difference of the time for exposure of former frame and time for exposure scope is greater than definite exposure time values reducing, the time for exposure of next frame is former frame time for exposure deducts definite exposure time values reducing; Otherwise the directly time for exposure using the lower limit of time for exposure scope as next frame;
Step (135): next frame image exposuring time increases, if the upper limit difference of the time for exposure of former frame and time for exposure scope is greater than the exposure time values of definite increase, time for exposure that is former frame time for exposure of next frame adds the exposure time values of definite increase; Otherwise the directly time for exposure using the higher limit of time for exposure scope as next frame.
2. automatic exposure control method according to claim 1, is characterized in that, it is (8R+R+4B+16G1+2G2+G2)/32 that described rgb color space closes to YUV colour space transformation, wherein:
G1 is the G component of strange passage;
G2 is the G component of even passage.
3. automatic exposure control method according to claim 1 and 2, it is characterized in that, described automatic exposure control method moves in FPGA is controlled in exposure, wherein, it is the anti-molten formula FPGA of space flight level that FPGA is controlled in exposure, and its model is the A54SX72A-CQ208B of Actel company.
4. automatic exposure control method according to claim 1, is characterized in that, the time for exposure gear of described automatic exposure control method is divided into two grades, and the time for exposure scope of a shelves is 4 μ s～140ms, and the time for exposure scope of b shelves is 16 μ s～560ms.
5. one kind for realizing the automatic exposure control device of automatic control exposal control method described in claim 1, it is characterized in that, this automatic exposure control device comprises optical lens (21), APS transducer (22), exposure control FPGA (23); Wherein, optical lens (21), APS transducer (22), exposure are controlled FPGA (23) and are placed successively,
Optical lens (21), for by target imaging to be imaged in APS transducer (22);
APS transducer (22), for converting optical signalling to electronic signal;
FPGA (23) is controlled in exposure, calculates, and the image brightness of gained image brightness and expection is compared for image brightness, determines the automatic exposure time.
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| CN105430293A (en) * | 2015-12-03 | 2016-03-23 | 哈尔滨工业大学 | In-orbit dynamic scene real-time matching method of optical remote sensing satellite |
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