CN103472501A - Cloud and aerial total cloud amount detection method and system - Google Patents
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Abstract
The invention discloses a cloud and aerial total cloud amount detection method and system. The system comprises an image obtaining device, a sky type confirming module, a cloud detection module and an aerial total cloud amount computing module, wherein the image obtaining device is used for obtaining an aerial cloud picture at a preset moment, the sky type confirming module is used for confirming the type of the sky at the preset moment, the cloud in the cloud picture is detected through the cloud detection module according to partition threshold values, and the aerial total cloud amount computing module is used for computing the aerial total cloud amount according to the ratio of the cloud in the aerial cloud picture to the whole aerial cloud picture. The cloud in the cloud picture is detected through the aerial cloud picture partition threshold values corresponding to the different sky types, the influences of different weather conditions on the detection result of the aerial cloud picture are taken into full consideration, and the accuracy of the cloud detection is made to be higher.
Description
Technical field
The present invention relates to the aerological sounding field, relate in particular to a kind of cloud detection method of optic and system of sky.
Background technology
Cloud amount refers to that obnubilation covers the one-tenth number in the sky visual field.The observation of cloud amount comprises Total-and low-cloud covers.The assembly number that when total amount of cloud refers to observation, sky is covered by all obnubilations, low cloud amount refers to that sky is hanged down the one-tenth number that cloud covered of family of clouds, all remembers integer.
Existing ground total amount of cloud observation procedure can be divided into artificial visually examine's method, the method for inversion and remotely sensed image method etc.Wherein, artificial visually examine's method is most domestic meteorological station the most frequently used cloud-cover observation method at present, but this mode has become a bottleneck of restriction surface weather observation robotization with very large subjectivity.
The method of inversion does not refer to and directly total amount of cloud is observed, and carry out the inverting total amount of cloud by other observation element, as adopting the spot measurement data, Laser-ceilometer carrys out inverting all-sky total amount of cloud by time integral, and multispectral rotation is covered shadow bands radiation gauge (Multi-filter Rotating Shadowband Radiometers, MFRSR) and is utilized the all-sky scattering flux under different-waveband to carry out inverting all-sky total amount of cloud by relevant radiation transformation model.But these inversion algorithms are desirable assumed conditionses based on some mostly, and that actual sky is difficult to is in full accord with it, thereby a kind of means of supplementing out economy that can only calculate as the all-sky total amount of cloud of the method for inversion.
The remotely sensed image method is mainly the mode that adopts remotely sensed image, takes facing up cloud atlas from ground, then adopts image processing algorithm to carry out cloud detection to calculate total amount of cloud, and this is the current Main Means that utilizes device to survey to observe total amount of cloud.Instrument based on the remotely sensed image method mainly contains total sky imager (Whole Sky Imager, WSI), total sky imager (Total Sky Imager, TSI) and all-sky imaging system (All-sky Imager System, ASIs) etc., these instruments have all been taked certain measure of blocking to the sun when obtaining the all-sky cloud atlas, to alleviate the impact of the sun on picture quality.But when the sun is blocked, need to be followed the tracks of the sun in real time, and this tracking means complex structure, and also can form the subregion in image when the sun is blocked simultaneously and block, this also will affect the precision that total amount of cloud is calculated to a certain extent.
In addition, aspect the cloud detection algorithm, mainly be based at present segmentation threshold, that is, but be that certain quantitative information in cloud atlas (for example brightness value of pixel or gray-scale value) sets segmentation threshold, but according to the relation of this quantitative information and this segmentation threshold (higher or lower than), each pixel is defined as to cloud or non-cloud, thereby the all-sky cloud atlas is divided into to cloud and non-cloud two parts, then adds up the ratio that cloud partly accounts for the all-sky cloud atlas, thereby obtain the all-sky total amount of cloud.But have been found that such method is lower for the computational accuracy of a part of all-sky cloud atlas total amount of cloud.
Summary of the invention
The present inventor finds, the precision why current cloud detection algorithm based on segmentation threshold calculates for the cloud amount of some cloud atlas is lower, an important reason is that these cloud detection algorithms are not all considered the impact of Sky Types factor when setting segmentation threshold, but different Sky Types is adopted to identical segmentation threshold or identical segmentation threshold setting means.
One of purpose of the present invention is to provide a kind of brand-new cloud detection and all-sky total amount of cloud detection method with a kind of brand-new design.Another object of the present invention is to improve the computational accuracy of cloud detection and the detection of all-sky total amount of cloud.
In order to realize above-mentioned at least one purpose, the invention provides a kind of cloud detection method of optic, comprising:
Image acquisition step: utilize image acquisition equipment to obtain the cloud atlas of the sky of predetermined instant;
Sky Types determining step: determine the Sky Types at the described sky of described predetermined instant; Wherein, described Sky Types is selected from a kind of of multiple default Sky Types for meaning the Cloud amount scope;
Cloud detection step: with segmentation threshold, detect the cloud in described cloud atlas; Wherein, described segmentation threshold according to from described multiple default Sky Types respectively a kind of in corresponding multiple different segmentation threshold setting means determine.
Preferably, in described Sky Types determining step, according to the information entropy of described cloud atlas, determine the described Sky Types at the described sky of described predetermined instant.
Preferably, the described information entropy of described cloud atlas is the monochrome information entropy of described cloud atlas or the half-tone information entropy of the gray-scale map corresponding with described cloud atlas.
Preferably, the computing formula of the described information entropy of described cloud atlas is:
Wherein, the information entropy that E is image,
and x (i, j) refers to the gray-scale value of the pixel in (i, j) position in the brightness value of the pixel in (i, j) position in described cloud atlas or the described gray-scale map corresponding with described cloud atlas.
Preferably, in the type determining step, also comprise described monochrome information entropy and default one or more information entropy threshold values are compared, to determine described Sky Types on high.
Preferably, described multiple default weather pattern comprises clear sky, cloudy day and cloudy.
Preferably, described multiple default weather pattern comprises clear sky, cloudy day and cloudy; Described one or more information entropy threshold value comprises the first and second information entropy threshold values, and described first information entropy threshold value is less than described the second information entropy threshold value; Wherein, in the situation that described monochrome information entropy is less than described first information entropy threshold value, determine that described Sky Types is for the cloudy day; In the situation that described monochrome information entropy is greater than described the second information entropy threshold value, determine that described Sky Types is cloudy; In the situation that described monochrome information entropy between described the first and second information entropy threshold values, determines that described Sky Types is clear sky.
Preferably, described first information entropy threshold value is selected from 1.9-2.1, and/or described the second information entropy threshold value is selected from 2.35-2.55.
Preferably, in described cloud detection step, also comprise the normalization difference processing of each pixel in described cloud atlas being carried out to blue red wave band, to obtain the Normalized Grey Level value of each pixel; And, described Normalized Grey Level value and described segmentation threshold are compared to determine the cloud in described cloud atlas.
Preferably, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is cloudy, described segmentation threshold adopts the adaptive threshold based on maximum between-cluster variance.
Preferably, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is cloudy, described segmentation threshold is μ-3 σ; Wherein, the average that μ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed, the variance that σ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed.
Preferably, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is clear sky, described segmentation threshold is μ+3 σ; Wherein, the average that μ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed, the variance that σ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed.
Preferably, also comprise the time shutter determining step: determine the time shutter that meets one or more predetermined conditions that described image acquisition equipment is used when described predetermined instant obtains described cloud atlas; Wherein, described one or more predetermined condition comprises: the first preselected area in described cloud atlas and the average brightness value of the second preselected area are all between the predetermined luminance upper limit and predetermined luminance lower limit; Described the second preselected area is less than and is contained in fully described the first preselected area.
Preferably, in described image acquisition step, described image acquisition equipment obtains described cloud atlas in the situation that do not block the sun.
Preferably, described cloud atlas is the all-sky cloud atlas.
The invention also discloses a kind of all-sky total amount of cloud detection method, comprise each step in above-mentioned cloud detection method of optic, also comprise the total amount of cloud calculation procedure: the ratio that accounts for whole described all-sky cloud atlas according to the cloud in described all-sky cloud atlas is calculated the sky total amount of cloud.
Preferably, in the situation that comprise sun image in described all-sky cloud atlas, described sky total amount of cloud does not comprise the ratio that described sun image accounts for whole described cloud atlas.
The invention also discloses a kind of cloud detection system, comprising:
Image acquisition equipment, for the cloud atlas of the sky that obtains predetermined instant;
The Sky Types determination module, for determining the Sky Types at the described sky of described predetermined instant; Wherein, described Sky Types is selected from a kind of of multiple default Sky Types for meaning the Cloud amount scope;
The cloud detection module, detect the cloud in described cloud atlas by segmentation threshold; Wherein, described segmentation threshold according to from described multiple default Sky Types respectively a kind of in corresponding multiple different segmentation threshold setting means determine.
Preferably, described Sky Types determination module is configured to determine the described Sky Types at the described sky of described predetermined instant according to the monochrome information entropy of described cloud atlas.
Preferably, described system also comprises: the automatic exposure module, for the time shutter that meets one or more predetermined conditions of determining that described image acquisition equipment is used when described predetermined instant obtains described cloud atlas; Wherein, described one or more predetermined condition comprises: the first preselected area in described cloud atlas and the average brightness value of the second preselected area are all between the predetermined luminance upper limit and predetermined luminance lower limit; Described the second preselected area is less than and is contained in fully described the first preselected area.
Preferably, described cloud atlas is the all-sky cloud atlas, and described image acquisition equipment is configured to not block in the situation of the sun and obtains described all-sky cloud atlas.
Preferably, in described Sky Types determination module, the computing formula of the described information entropy of described cloud atlas is:
Wherein, the information entropy that E is image,
and the gray-scale value of the pixel in (i, j) position in the brightness value of the pixel in (i, j) position in the described cloud atlas of x (i, j) or the described gray-scale map corresponding with described cloud atlas.
Preferably, in described Sky Types determination module, also comprise described monochrome information entropy and default one or more information entropy threshold values are compared, to determine described Sky Types.
Preferably, described multiple default weather pattern comprises clear sky, cloudy day and cloudy; Described one or more information entropy threshold value comprises the first and second information entropy threshold values, and described first information entropy threshold value is less than described the second information entropy threshold value; Wherein, in the situation that described monochrome information entropy is less than described first information entropy threshold value, determine that described Sky Types is for the cloudy day; In the situation that described monochrome information entropy is greater than described the second information entropy threshold value, determine that described Sky Types is cloudy; In the situation that described monochrome information entropy between described the first and second information entropy threshold values, determines that described Sky Types is clear sky.
Preferably, described first information entropy threshold value is selected from 1.9-2.1, and/or described the second information entropy threshold value is selected from 2.35-2.55.
Preferably, in described cloud detection module, also comprise the normalization difference processing of each pixel in described cloud atlas being carried out to blue red wave band, to obtain the Normalized Grey Level value of each pixel; And, described Normalized Grey Level value and described segmentation threshold are compared to determine the cloud in described cloud atlas.
Preferably, in described cloud detection module, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is cloudy, described segmentation threshold adopts the adaptive threshold based on maximum between-cluster variance.
Preferably, in described cloud detection module, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is cloudy, described segmentation threshold is μ-3 σ; Wherein, the average that μ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed, the variance that σ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed.
Preferably, in described cloud detection module, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is clear sky, described segmentation threshold is μ+3 σ; Wherein, the average that μ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed, the variance that σ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed.
The invention also discloses a kind of all-sky total amount of cloud detection system, comprise the modules in above-mentioned cloud detection system, also comprise all-sky total amount of cloud computing module, the ratio that accounts for whole described all-sky cloud atlas for the cloud according to described all-sky cloud atlas is calculated the sky total amount of cloud.
Preferably, in described cloud detection module, in described cloud atlas, comprise in the situation of sun image, described Cloud amount does not comprise the ratio that described sun image accounts for whole described cloud atlas.
Technical scheme of the present invention has following beneficial effect:
(1) according to method and system of the present invention, segmentation threshold that can be corresponding with different Sky Types detects the cloud in cloud atlas, has taken into full account the impact of different states of the sky on sky cloud atlas testing result, makes the cloud detection precision higher;
(2) according to method and system of the present invention, the monochrome information entropy of the sky cloud atlas that obtains and default one or more information entropy threshold values can be compared, thereby determine Sky Types, without artificial interference, more accurately and automaticity high;
(3), according to method and system of the present invention, image acquisition equipment can obtain cloud atlas with time shutter preferably at predetermined instant, to obtain the good sky cloud atlas of imaging, can improve equally the precision of cloud detection;
Further, by regulating the time shutter, image acquisition equipment can obtain the good cloud atlas of imaging in the situation that do not block the sun, this has been avoided because need to block the sun and use complicated sun tracker, and has also avoided due to the cloud amount error of calculation caused of blocking of blocking the solar time other in image do not wished the zone of blocking.
(4) each step of method of the present invention can realize automatically by computer program, this for cloud detection particularly the cloud amount automatic Observation new solution is provided.
According to hereinafter, by reference to the accompanying drawings to the detailed description of the specific embodiment of the invention, those skilled in the art will understand above-mentioned and other purposes, advantage and feature of the present invention more.
The accompanying drawing explanation
Hereinafter describe specific embodiments more of the present invention in detail in exemplary and nonrestrictive mode with reference to the accompanying drawings.In accompanying drawing:
The process flow diagram of Fig. 1 cloud detection of the present invention and all-sky total amount of cloud detection method;
Fig. 2 time shutter of the present invention is determined the process flow diagram of method;
Fig. 3 (a), Fig. 3 (b) and Fig. 3 (c) show the sky cloud atlas of the different Sky Types of three width;
The structural representation of Fig. 4 cloud detection of the present invention and all-sky total amount of cloud detection system.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in more detail.
As shown in fig. 1, wherein image acquisition step, Sky Types determining step and cloud detection step can form according to cloud detection method of optic of the present invention, are preferably in image acquisition step and also comprise the time shutter determining step before.In addition, by after the cloud detection step at this cloud detection method of optic, increasing the total amount of cloud calculation procedure, can form according to total amount of cloud detection method of the present invention.
image acquisition step
Image acquisition step is to utilize image acquisition equipment to obtain the sky cloud atlas of predetermined instant.The image that comprises the aerial presumptive area in sky of observation to some extent in this sky cloud atlas.For cloud detection, particularly, in calculating this important application scenario of all-sky total amount of cloud, this sky cloud atlas can be the image of all-sky usually.Can utilize in prior art existing various total sky imagers or full visual field recording geometry can obtain the all-sky cloud atlas of whole sky basically.In other cloud detection occasion, this sky cloud atlas can be also the image of local sky.
In one embodiment, when obtaining cloud atlas, image acquisition equipment can not blocked the sun.So just can avoid comprising baroque sun tracker in image acquisition equipment, but also can avoid owing to blocking the sun adverse effect that cloud detection or cloud amount computational accuracy are caused.For cloud amount, calculate, the obtaining of cloud atlas normally carried out at a certain time interval, such as 10 minutes once.Accordingly; according to the present invention, can to the sun, not carry out any blocking when obtaining cloud atlas sky being carried out to imaging, and in the non-imaging period; can select the whole visual field of image acquisition equipment is blocked entirely, with the protection imaging device, can not be exposed to the sun and damage for a long time because of the sun.
When by image acquisition equipment, the sky cloud atlas being carried out to imaging, different weather conditions meetings cause different illumination conditions.Particularly for example in the situation that the sun is not blocked while obtaining cloud atlas, may due to the existence of the sun whether and the image quality of image acquisition equipment is caused to adverse effect.If adopt the fixing time shutter to carry out imaging to different weather conditions, can make the sky cloud atlas present under-exposed or over-exposed phenomenon.Therefore, the time shutter in the time of can adopting suitable automatic exposure scheme to control image acquisition equipment to carry out imaging, thus eliminate well the impact of the sun on cloud atlas picture quality, to obtain the good sky cloud atlas of imaging.
Therefore, before image acquisition step, preferably by the time shutter determining step, determine the time shutter of image acquisition equipment.
the time shutter determining step
For the ease of robotization, realize, the time shutter of image acquisition equipment can be determined by making it meet one or more predetermined conditions.In one embodiment, these one or more predetermined conditions can comprise: the first preselected area in cloud atlas and the average brightness value of the second preselected area are all between the predetermined luminance upper limit and predetermined luminance lower limit.Wherein, the second preselected area is less than and is contained in fully the first preselected area.In another embodiment, predetermined condition can also comprise that the time shutter should be between the time shutter of the image acquisition equipment upper limit and time shutter lower limit.In yet another embodiment, determining for fear of the time of costing a lot of money that time shutter, predetermined condition can also be included in by iterative process obtains in the process of optimum exposure time the restriction of iterations in other words of full test number of times.In other embodiments, can also determine the time shutter by the predetermined condition of setting other.
Below in conjunction with a specific embodiment having described time shutter determining step of the present invention since Fig. 2.Before the flow process that starts Fig. 2, need to preset some parameters.These parameters can comprise sets the first and second preselected areas, the predetermined luminance upper limit, predetermined luminance lower limit, the time shutter upper limit, time shutter lower limit and full test number of times.
For the all-sky cloud atlas that adopts fish eye lens to take, its effective areas imaging is a border circular areas.For such cloud atlas, in one embodiment, the first preselected area is the effective coverage of whole all-sky cloud atlas, i.e. zone after original all-sky fish eye images removal black surround.Second preselected area is centered by image center, specifies a small circular zone of radius, and this radius generally can be chosen as 50-100 pixel.In other embodiments, also can adopt other suitable mode to select the first and second preselected areas.
In step 101, set the initial exposure time.
In step 102, adopt above-mentioned initial exposure time to take a sky image and be saved to the buffer memory of computing machine.
In step 103, calculate the first and second preselected areas average brightness value separately in the above-mentioned image obtained.
In step 104, need to judge according to average brightness value, current time shutter and the iterations of arbitrary preselected area in above-mentioned the first and second preselected areas whether the current time shutter is optimum exposure time.
Particularly, when the average brightness value of arbitrary preselected area is greater than the mean flow rate upper limit of setting, and the time shutter of current employing is greater than the time shutter lower limit of setting, and iterations is less than the full test number of times of setting, shows that the image that adopts the current time shutter to gather is excessively bright.
When the average brightness value of arbitrary preselected area is less than the mean flow rate lower limit of setting, and the time shutter of current employing is less than the time shutter upper limit of setting, and iterations is less than the full test number of times of setting, show that the image that adopts the current time shutter to gather is excessively dark.
Otherwise, show that the current time shutter is suitable, enter step 105 and complete automatic exposure.
In step 106, according to the judged result in step 104, determine that adopting the image that the current time shutter obtains is " excessively bright " or " excessively dark ", and in step subsequently, the time shutter is taked to corresponding different disposal.When image " excessively bright ", enter step 107; When image " excessively dark ", enter step 108.
In step 107, judge whether it is to regulate the time shutter first.
When judgment result is that of step 107 is, enter step 701, will reduce by half the time shutter, and in step 109, the time shutter after reducing by half is set as to the new time shutter.
When the determination result is NO, enter step 702 when step 107.
In step 702, judge whether time shutter last time is greater than the current time shutter.If be greater than, carry out step 701; If be not more than, carry out step 703.
In step 703, calculate current and mean value time shutter last time, and in step 109, this mean value is set as to the new time shutter.
Similarly, in step 108, judge whether it is to regulate the time shutter first.
When judgment result is that of step 108 is, enter step 801, will double the time shutter, and in step 109, the time shutter after doubling is set as to the new time shutter.
When the determination result is NO, enter step 802 when step 108.
In step 802, judge whether time shutter last time is less than the current time shutter.If be less than, carry out step 801; If be not less than, carry out step 803.
In step 803, calculate current and mean value time shutter last time, and in step 109, this mean value is set as to the new time shutter.
Set the new time shutter in step 109 after, return to again step 102, adopt the new time shutter to continue to gather image, until meet brightness conditions to obtain optimum exposure time or to reach the full test number of times in step 104, and complete the automatic exposure process in step 105.
It will be appreciated that, but above-described time shutter determining step is preferred non-essential in the present invention.In other embodiments, in the situation that suitable, also can manually according to experience, set the time shutter.Also it will be appreciated that, above-described time shutter determining step is not limited to according in cloud detection method of optic of the present invention, but can be applied to any other suitable needs, obtains in the application scenario of sky image.
the Sky Types determining step
The Sky Types determining step is for determining the Sky Types at the described sky of described predetermined instant.Wherein, described Sky Types is selected from a kind of of multiple default Sky Types for meaning the Cloud amount scope.
In one embodiment, the Sky Types in the time of can judging imaging according to the information entropy of sky cloud atlas.In one embodiment, Sky Types can be preset and is divided into clear sky, cloudy day and cloudy.Wherein, the sky in the time of the all-sky total amount of cloud can being less than to 1 one-tenth is called clear sky, and the sky that can be 10 one-tenth by the all-sky total amount of cloud is called the cloudy day, and total amount of cloud being called between 1-10 is cloudy.For clear sky, cloudy day and cloudy three kinds of Sky Types, can be with reference to the all-sky cloud atlas of the different Sky Types of three width as shown in Figure 3, wherein, Fig. 3 (a) is clear sky, and Fig. 3 (b) is cloudy, and Fig. 3 (c) is the cloudy day.
The quantity of information that the all-sky cloud atlas of different Sky Types comprises is different, and the information entropy of image just in time can be used for characterizing the difference of this quantity of information.Information entropy can be the monochrome information entropy of cloud atlas or the half-tone information entropy of the gray-scale map corresponding with cloud atlas.It should be noted that, for color cloud picture, its brightness can be equal to the gray scale in the gray-scale map that this cloud atlas is corresponding.
The computing formula of image information entropy is:
Wherein, the information entropy that E is image,
and x (i, j) refers to the gray-scale value of the pixel in (i, j) position in the brightness value of the pixel in (i, j) position in described cloud atlas or the described gray-scale map corresponding with described cloud atlas.
After obtaining information entropy by above-mentioned computing formula, described information entropy and default one or more information entropy threshold values can be compared, to determine described Sky Types.When Sky Types being divided into to three kinds like that as mentioned before, for example clear sky, cloudy day and when cloudy, can be by setting two information entropy threshold values, that is, the first and second information entropy threshold values, determine Sky Types.Particularly, obtained information entropy and default the first and second information entropy threshold values can be compared, to determine Sky Types, wherein first information entropy threshold value is less than the second information entropy threshold value.
By analyzing the all-sky cloud atlas of a large amount of different Sky Types, can find, the information entropy minimum of cloudy image, generally below 2.0; The information entropy maximum of very cloudy sky image, generally can be more than 2.45; And the information entropy of clear sky image is between 2.0-2.45.Like this, can be 2.0 by first information entropy Threshold, by the second information entropy Threshold, be 2.45.In the situation that information entropy is less than first information entropy threshold value, determine that Sky Types is the cloudy day; In the situation that information entropy is greater than the second information entropy threshold value, determine that Sky Types is cloudy; In the situation that information entropy between the first and second information entropy threshold values, determines that described Sky Types is clear sky.It will be appreciated that, the first and second information entropy threshold values also can depart from respectively 2.0 and 2.45 slightly.For example, first information entropy threshold value can be selected between 1.9-2.1, and/or the second information entropy threshold value can be selected between 2.35-2.55.
In other embodiments, when default Sky Types is more or less, corresponding more or less information entropy threshold value also can be set.For example, when default Sky Types only has two kinds, just only need a default information entropy threshold value; When default weather pattern is four kinds, just can preset three information entropy threshold values.The concrete numerical value of each threshold value also can obtain by the all-sky cloud atlas of analyzing a large amount of different Sky Types, repeats no more herein.
Although determine that by the information entropy of cloud atlas itself Sky Types is conducive to the judgement that robotization realizes Sky Types, be appreciated that the present invention is not limited to such Sky Types and determines mode.In other embodiments, also can determine by other means Sky Types, such as can directly estimating, roughly judge Sky Types.
the cloud detection step
In the cloud detection step, be to detect the cloud in described cloud atlas with segmentation threshold.Wherein, described segmentation threshold according to from described multiple default Sky Types respectively a kind of in corresponding multiple different segmentation threshold setting means determine.In a specific embodiment, can be that different Sky Types is adopted to multiple different Threshold segmentation mode, thereby obtain the corresponding segmentation threshold of different Sky Types, again each pixel in the cloud atlas obtained is carried out the normalization difference processing of blue red wave band, to obtain the Normalized Grey Level value of each pixel, finally the Normalized Grey Level value is compared to determine the cloud in cloud atlas with above-mentioned corresponding segmentation threshold.
Normalized is mainly that the blue wave band of all-sky cloud atlas and red wave band are carried out to the processing be shown below:
Wherein, N is the Normalized Grey Level value, and B is the blue wave band gray-scale value, and R is red band grey data.
In one embodiment, when default Sky Types is previously described clear sky, cloudy and cloudy this three types, can adopt respectively corresponding different segmentation threshold setting means.Alternatively or preferably, type is that in cloudy situation, its segmentation threshold can adopt the adaptive threshold based on maximum between-cluster variance on high; Type is that in cloudy situation, its segmentation threshold can be μ-3 σ on high; In the situation that type is clear sky on high, its segmentation threshold is μ+3 σ.Wherein, the average that μ is the Normalized Grey Level value of described cloud atlas after the normalization difference is processed, the variance that σ is the Normalized Grey Level value of cloud atlas after the normalization difference is processed.
Based on determined segmentation threshold, can judge that in cloud atlas, the image of each pixel is cloud or non-cloud.For example to be greater than the pixel of segmentation threshold be non-cloud to the Normalized Grey Level value, and the pixel that is less than segmentation threshold is cloud.
It will be appreciated that, although described above for different Sky Types, adopt optionally or segmentation threshold setting means preferably, basic conception of the present invention is to adopt different segmentation threshold setting meanss for different Sky Types.Therefore, for a certain Sky Types, the setting means of its segmentation threshold does not limit to and hereinbefore described type yet, but can adopt other suitable segmentation threshold setting means.For example, when Sky Types while being cloudy, the setting means of its segmentation threshold can be fixed threshold algorithm, global threshold algorithm and local threshold interpolation algorithm etc., because this algorithm and previously described adaptive threshold based on maximum between-cluster variance have all applied in existing cloud detection method of optic, so repeat no more herein.
When default Sky Types has more kinds of type, corresponding segmentation threshold setting means also can correspondingly be taked more kinds of types.
The total amount of cloud calculation procedure
An important application occasion of cloud detection is to calculate Cloud amount.Now, can be added up the pixel that belongs to cloud or non-cloud in cloud atlas, the ratio that accounts for whole cloud atlas according to the cloud in cloud atlas is calculated Cloud amount.When cloud atlas is the all-sky cloud atlas, be that the ratio that accounts for whole all-sky cloud atlas according to the cloud in the all-sky cloud atlas is calculated the sky total amount of cloud.As previously mentioned, according to the present invention, can obtain cloud atlas in the situation that do not block the sun.Therefore, under these circumstances, if comprise sun image in cloud atlas, also need to remove the impact that calculate cloud amount in sun zone when calculating the all-sky total amount of cloud.Obtain the method in the zone of sun image in prior art in existing image on high, do not repeat them here.
It will be appreciated that, according to method of the present invention, can be in the situation that the sun not be blocked to the cloud detection result that obtains degree of precision, but method of the present invention equally also is suitable in the situation that the sun is blocked to obtained cloud atlas.
Cloud detection system and all-sky total amount of cloud detection system
In Fig. 4, image acquisition equipment 1, Sky Types determination module 2 and cloud detection module 3, and preferred automatic exposure module 5 can form according to cloud detection system of the present invention.By increase all-sky total amount of cloud computing module 4 in this cloud detection system, can form according to all-sky total amount of cloud detection system of the present invention.Wherein, for Sky Types determination module 2, cloud detection module 3, automatic exposure module 5 and all-sky total amount of cloud computing module 4, can by the computing machine (shown in the empty frame in Fig. 4) that specific program is housed, realize respectively.
Sky Types determination module 2 is for determining the Sky Types at the described sky of described predetermined instant, and Sky Types is selected from a kind of of multiple default Sky Types for meaning the Cloud amount scope.Sky Types determination module 2 can be configured to determine corresponding Sky Types according to the information entropy of cloud atlas.This information entropy can be the monochrome information entropy of cloud atlas or the half-tone information entropy of the gray-scale map corresponding with this cloud atlas, for example, shown in formula (1).Sky Types determination module 2 can carry out work according to the Sky Types determining step of describing above.
All-sky total amount of cloud computing module 4 is added up for the pixel that belongs to cloud or non-cloud to cloud atlas, and the ratio that accounts for whole cloud atlas according to the cloud in cloud atlas is calculated Cloud amount.When cloud atlas is the all-sky cloud atlas, be that the ratio that accounts for whole all-sky cloud atlas according to the cloud in the all-sky cloud atlas is calculated the sky total amount of cloud.
In order to make image acquisition equipment 1 can obtain the good cloud atlas of imaging, can utilize automatic exposure module 4 to determine the time shutter that meets one or more predetermined conditions that image acquisition equipment 1 is used when obtaining cloud atlas.Particularly, automatic exposure module 5 can be carried out work according to the time shutter determining step of describing above.Particularly, the predetermined condition of using in definite time shutter comprises: the first preselected area in cloud atlas and the average brightness value of the second preselected area are all between the predetermined luminance upper limit and predetermined luminance lower limit.Wherein, the second preselected area is less than and is contained in fully the first preselected area.
For the sky imaging, image acquisition equipment 1 can be exposed in external environment for a long time.Can be because the sun is exposed to the sun and damages for a long time for fear of the image-generating unit of image acquisition equipment 1, can in image acquisition equipment 1, provide and block assembly and cover image-generating unit fully.Existing image acquisition equipment 1 has adopted for example movable spherical limb or horizontal sunshading board to be used as the required assembly that blocks.Need to understand, the assembly that blocks so only carries out integral body to image-generating unit and covers when not needing imaging, this be different from " background technology " part while being described in imaging only to image in the regional area of the corresponding sun shield element of being blocked, the latter need to could be covered the sun with the sun tracker collaborative work not in the same time all in imaging the time.For image acquisition equipment 1 of the present invention, as described in above when describing cloud detection method of optic of the present invention, allow to obtain described cloud atlas in the situation that do not block the sun, that is to say, can comprise sun image in the cloud atlas obtained.Therefore, in the present invention, the shield element that image acquisition equipment 1 is covered the sun in the time of can being omitted in imaging and corresponding sun tracker.That is to say, according to the present invention, can when the cloud atlas imaging, to the sun, not carry out any blocking, and in the non-imaging period, whole visual field be blocked entirely, with for example image-generating unit in the protection image acquisition equipment.
So far, those skilled in the art will recognize that, illustrate and described a plurality of exemplary embodiment of the present invention although this paper is detailed, but, without departing from the spirit and scope of the present invention, still can directly determine or derive many other modification or the modification that meets the principle of the invention according to content disclosed by the invention.Therefore, scope of the present invention should be understood and regard as and cover all these other modification or modifications.
Claims (18)
1. a cloud detection method of optic comprises:
Image acquisition step: utilize image acquisition equipment to obtain the cloud atlas of the sky of predetermined instant;
Sky Types determining step: determine the Sky Types at the described sky of described predetermined instant; Wherein, described Sky Types is selected from a kind of of multiple default Sky Types for meaning the Cloud amount scope;
Cloud detection step: with segmentation threshold, detect the cloud in described cloud atlas; Wherein, described segmentation threshold according to from described multiple default Sky Types respectively a kind of in corresponding multiple different segmentation threshold setting means determine.
2. method according to claim 1, is characterized in that, in described Sky Types determining step, according to the monochrome information entropy of described cloud atlas, determines the described Sky Types at the described sky of described predetermined instant.
3. method according to claim 2, is characterized in that, in the type determining step, also comprises described monochrome information entropy and default one or more information entropy threshold values are compared, to determine described Sky Types on high.
4. method according to claim 3, is characterized in that, described multiple default weather pattern comprises clear sky, cloudy day and cloudy; Described one or more information entropy threshold value comprises the first and second information entropy threshold values, and described first information entropy threshold value is less than described the second information entropy threshold value;
Wherein, in the situation that described monochrome information entropy is less than described first information entropy threshold value, determine that described Sky Types is for the cloudy day; In the situation that described monochrome information entropy is greater than described the second information entropy threshold value, determine that described Sky Types is cloudy; In the situation that described monochrome information entropy between described the first and second information entropy threshold values, determines that described Sky Types is clear sky.
5. method according to claim 4, is characterized in that, described first information entropy threshold value is selected from 1.9-2.1, and/or described the second information entropy threshold value is selected from 2.35-2.55.
6. according to the described method of any one in claim 1-5, it is characterized in that, in described cloud detection step, also comprise the normalization difference processing of each pixel in described cloud atlas being carried out to blue red wave band, to obtain the Normalized Grey Level value of each pixel; And, described Normalized Grey Level value and described segmentation threshold are compared to determine the cloud in described cloud atlas.
7. method according to claim 6, is characterized in that, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is cloudy, described segmentation threshold adopts the adaptive threshold based on maximum between-cluster variance.
8. according to the described method of any one in claim 6-7, it is characterized in that, described multiple segmentation threshold setting means comprises: in the situation that described Sky Types is cloudy, described segmentation threshold is μ-3 σ; In the situation that described Sky Types is clear sky, described segmentation threshold is μ+3 σ;
Wherein, the average that μ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed, the variance that σ is the described Normalized Grey Level value of described cloud atlas after described normalization difference is processed.
9. according to the described method of any one in claim 1-8, it is characterized in that, also comprise the time shutter determining step: determine the time shutter that meets one or more predetermined conditions that described image acquisition equipment is used when described predetermined instant obtains described cloud atlas;
Wherein, described one or more predetermined condition comprises: the first preselected area in described cloud atlas and the average brightness value of the second preselected area are all between the predetermined luminance upper limit and predetermined luminance lower limit; Described the second preselected area is less than and is contained in fully described the first preselected area.
10. according to the described method of any one in claim 1-9, it is characterized in that, in described image acquisition step, described image acquisition equipment obtains described cloud atlas in the situation that do not block the sun.
11. according to the described method of any one in claim 1-10, it is characterized in that, described cloud atlas is the all-sky cloud atlas.
12. an all-sky total amount of cloud detection method, comprise the described method of claim 11, also comprises the total amount of cloud calculation procedure: the ratio that accounts for whole described all-sky cloud atlas according to the cloud in described all-sky cloud atlas is calculated the sky total amount of cloud.
13. method according to claim 12, is characterized in that, in the situation that comprise sun image in described all-sky cloud atlas, described sky total amount of cloud does not comprise the ratio that described sun image accounts for whole described cloud atlas.
14. a cloud detection system comprises:
Image acquisition equipment, for the cloud atlas of the sky that obtains predetermined instant;
The Sky Types determination module, for determining the Sky Types at the described sky of described predetermined instant; Wherein, described Sky Types is selected from a kind of of multiple default Sky Types for meaning the Cloud amount scope;
The cloud detection module, detect the cloud in described cloud atlas by segmentation threshold; Wherein, described segmentation threshold according to from described multiple default Sky Types respectively a kind of in corresponding multiple different segmentation threshold setting means determine.
15. cloud detection system according to claim 17, is characterized in that, described Sky Types determination module is configured to determine the described Sky Types at the described sky of described predetermined instant according to the monochrome information entropy of described cloud atlas.
16. according to the described cloud detection system of claims 14 or 15, it is characterized in that, also comprise:
The automatic exposure module, for the time shutter that meets one or more predetermined conditions of determining that described image acquisition equipment is used when described predetermined instant obtains described cloud atlas;
Wherein, described one or more predetermined condition comprises: the first preselected area in described cloud atlas and the average brightness value of the second preselected area are all between the predetermined luminance upper limit and predetermined luminance lower limit; Described the second preselected area is less than and is contained in fully described the first preselected area.
17. according to the described cloud detection system of any one in claim 14-16, it is characterized in that, described cloud atlas is the all-sky cloud atlas, described image acquisition equipment is configured to not block in the situation of the sun and obtains described all-sky cloud atlas.
18. an all-sky total amount of cloud detection system, comprise the described cloud detection system of claim 17, also comprises all-sky total amount of cloud computing module, the ratio that accounts for whole described all-sky cloud atlas for the cloud according to described all-sky cloud atlas is calculated the sky total amount of cloud.
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