A method and apparatus for measuring target-to-background luminance contrast

Abstract

The application provides a target and background brightness contrast measurement method and device, the method comprising: taking pictures of the target and the background respectively, converting the RGB value of each pixel in the target picture and the background picture into the Y value in the CIE-XYZ spectral tristimulus value to obtain a target Y value graph and a background Y value graph, dividing the target into N regions according to the target Y value graph, dividing the background into N sub-regions according to the background Y value graph, selecting a point in each sub-region of the target and the background respectively, measuring the brightness coefficient of the point through multi-angle and multiple times and calculating the average value, weighting the average brightness coefficient in each sub-region of the target and the background through area to obtain a target brightness coefficient calculation value and a background brightness coefficient calculation value respectively, and calculating the brightness contrast of the target and the background according to the target brightness coefficient calculation value and the background brightness coefficient calculation value. The application improves the accuracy of the point measurement and the area measurement of the brightness coefficient, thereby improving the accuracy of the target and the background brightness.

Description

Technical Field

[0001] This invention specifically relates to a method and apparatus for measuring the brightness contrast between a target and a background. Background Technology

[0002] A field spectrometer can decompose sunlight reflected from ground objects into specific wavelength ranges. By capturing and analyzing the light information, it obtains the reflectivity curves of ground objects in each wavelength range, thereby obtaining the object's brightness coefficient. The average brightness coefficients of the target area and the background area are measured separately as calculated values, and the brightness contrast between the target and the background is calculated using a formula.

[0003] The existing method for measuring the brightness coefficients of targets and backgrounds involves randomly selecting 30 measurement points on both the background and the target, measuring the brightness coefficients of the 30 points on each side using a field spectrometer, and then averaging the results to obtain the calculated brightness coefficients of the target and background.

[0004] However, existing measurement methods have the following shortcomings: the selection of 30 measurement points is arbitrary, and the consistency between the average brightness coefficient of the 30 points and the average brightness coefficient of the area under test cannot be guaranteed; the instrument azimuth angles of the 30 measurement points are not completely consistent, and measurement errors are inevitable. Therefore, the brightness comparison obtained by existing measurement methods is arbitrary and contains measurement errors. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-precision, simple and practical method for measuring the brightness comparison between a target and the background, which addresses the above-mentioned deficiencies in the prior art, and also provides a corresponding device for implementing the method.

[0006] The technical solution adopted to solve the technical problem of this invention is:

[0007] This invention provides a method for measuring the brightness contrast between a target and a background, comprising:

[0008] Take separate photos of the target and background, and convert the RGB values ​​of each pixel in both photos to Y values ​​in the CIE-XYZ spectral tristimulus values, thus obtaining target Y value maps and background Y value maps.

[0009] Based on the target's Y-value map, the target is divided into N regions; based on the background's Y-value map, the background is divided into N partitions.

[0010] Select any point within each section of both the target and the background, measure the brightness coefficient of that point multiple times from multiple angles, and calculate the average value.

[0011] The average brightness coefficients of the target and background within their respective N partitions are weighted by area to obtain the calculated values ​​for the target brightness coefficient and the background brightness coefficient, respectively.

[0012] The brightness comparison between the target and the background is calculated based on the target brightness coefficient and the background brightness coefficient.

[0013] Optionally,

[0014] If the main objective is to prevent satellite reconnaissance during the day, the photo should be taken directly above the target and background areas, at noon, with the sun's zenith angle less than 50° and the observation angle less than 10°.

[0015] Optionally,

[0016] The background in the background photo represents the typical optical characteristics of the target area, and the background area is no less than 9 times the size of the target area.

[0017] Optionally,

[0018] N is between 10 and 30.

[0019] Optionally,

[0020] The brightness coefficient of the point was measured multiple times from multiple angles using a field spectrometer, and the average value was calculated.

[0021] The testing angle of the field spectrometer is perpendicular to the angle of sunlight incidence, and the azimuth angle φ of the field spectrometer is... r With the solar azimuth angle φ i The specific relationships are as follows:

[0022] φ i +45<φ r <φ i +135 or φ i -45<φ r <φ i -135.

[0023] Optionally,

[0024] The area weighting is calculated using equation (1):

[0025]

[0026] Where r represents the calculated brightness coefficient of the target or background, and S represents the total area of ​​the target or background region. i S represents the average luminance coefficient of the i-th partition. i This represents the area of ​​the i-th partition.

[0027] Optionally,

[0028] The brightness comparison is calculated using equation (2):

[0029]

[0030] Where K represents the brightness contrast, r0 represents the calculated value of the target brightness coefficient, and r b This represents the calculated value of the background brightness coefficient.

[0031] The present invention also provides an apparatus for implementing the above-described target-background brightness contrast measurement method, comprising:

[0032] A camera is used to take pictures of the target and the background separately.

[0033] The conversion module is used to convert the RGB values ​​of each pixel in the target photo and the background photo into Y values ​​in the CIE-XYZ spectral tristimulus values, respectively, to obtain the target Y value map and the background Y value map.

[0034] The partitioning module is used to divide the target photo into N partitions based on the target Y-value map, and also to divide the background photo into N partitions based on the background Y-value map.

[0035] A field spectrometer is used to measure the brightness coefficient multiple times from multiple angles at any point selected within each section of the target and background.

[0036] The first calculation module is used to calculate the average value of the brightness coefficient of each selected point in each partition of the target and the background from multiple angles and multiple measurements.

[0037] The second calculation module is used to calculate the target brightness coefficient and the background brightness coefficient by weighting the average brightness coefficients within N zones of both the target and the background by area.

[0038] The third calculation module is used to calculate the brightness comparison between the target and the background based on the calculated values ​​of the target brightness coefficient and the background brightness coefficient.

[0039] This invention improves the accuracy of point measurements by measuring the brightness coefficient of a point multiple times from multiple angles instead of a single measurement. It also improves the accuracy of area measurements by dividing the region into zones using a Y-value map and calculating the average brightness coefficient of the region after area weighting of each measurement point, instead of calculating the average brightness coefficient of any 30 randomly selected points within the region. This invention is simple and practical, enabling the calculation of brightness comparisons through simple measurements; it is easy to operate and highly accurate. Attached Figure Description

[0040] Figure 1 This is a flowchart of the target and background brightness comparison measurement method provided in Embodiment 1 of the present invention;

[0041] Figure 2 Requirements for the solar zenith angle and instrument observation angle when taking photos with a camera or testing with a spectrometer;

[0042] Figure 3 This refers to the required azimuth angle of the instrument during spectrometer testing. Detailed Implementation

[0043] The technical solutions of the invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without creative effort are within the scope of the invention.

[0044] In the description of this invention, it should be noted that the use of terms such as "above" to indicate orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings and is only for the purpose of facilitating and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0045] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connection," "setting," "installation," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] This invention provides a method for measuring the brightness contrast between a target and a background, comprising:

[0048] Take separate photos of the target and background, and convert the RGB values ​​of each pixel in both photos to Y values ​​in the CIE-XYZ spectral tristimulus values, thus obtaining target Y value maps and background Y value maps.

[0049] Based on the target's Y-value map, the target is divided into N regions; based on the background's Y-value map, the background is divided into N partitions.

[0050] Select any point within each section of both the target and the background, measure the brightness coefficient of that point multiple times from multiple angles, and calculate the average value.

[0051] The average brightness coefficients of the target and background within their respective N partitions are weighted by area to obtain the calculated values ​​for the target brightness coefficient and the background brightness coefficient, respectively.

[0052] The brightness comparison between the target and the background is calculated based on the target brightness coefficient and the background brightness coefficient.

[0053] The present invention also provides an apparatus for implementing the above-described target-background brightness contrast measurement method, comprising:

[0054] A camera is used to take pictures of the target and the background separately.

[0055] The conversion module is used to convert the RGB values ​​of each pixel in the target photo and the background photo into Y values ​​in the CIE-XYZ spectral tristimulus values, respectively, to obtain the target Y value map and the background Y value map.

[0056] The partitioning module is used to divide the target photo into N partitions based on the target Y-value map, and also to divide the background photo into N partitions based on the background Y-value map.

[0057] A field spectrometer is used to measure the brightness coefficient multiple times from multiple angles at any point selected within each section of the target and background.

[0058] The first calculation module is used to calculate the average value of the brightness coefficient of each selected point in each partition of the target and the background from multiple angles and multiple measurements.

[0059] The second calculation module is used to calculate the target brightness coefficient and the background brightness coefficient by weighting the average brightness coefficients within N zones of both the target and the background by area.

[0060] The third calculation module is used to calculate the brightness comparison between the target and the background based on the calculated values ​​of the target brightness coefficient and the background brightness coefficient.

[0061] Example 1:

[0062] like Figure 1 As shown, this embodiment provides a method for measuring the brightness contrast between a target and the background, including:

[0063] First, take photos of the target and background separately using a digital camera. The location and time of taking the photos depend on the detection methods that this invention needs to defend against. If the main defense is against satellite reconnaissance during the day, the photo should be taken directly above the target and background areas at noon, requiring the solar zenith angle to be less than 50° and the observation angle to be less than 10°, as shown in the attached diagram. Figure 2 As shown. Additionally, the background in the photograph must represent the typical optical characteristics of the target area, and the background area must be at least nine times the size of the target area.

[0064] Then, the RGB values ​​of each pixel in both the target and background images are converted to Y values ​​in the CIE-XYZ spectral tristimulus values, resulting in target Y value maps and background Y value maps. Different conversion equations are selected based on the image format; a typical conversion equation for sRGB format is:

[0065] Y=0.2126R+0.7152G+0.0722B.

[0066] Then, the target is divided into N regions based on the target Y-value map, and the background is divided into N partitions based on the background Y-value map. Theoretically, the larger N is, the higher the accuracy, but the greater the measurement workload. It is recommended that the N value be between 10 and 30. Since there is a one-to-one correspondence between the Y-value and the brightness coefficient, the brightness coefficient of each region after partitioning is approximately the same.

[0067] Select any point within each section of the target and background, measure the brightness coefficient of that point multiple times from multiple angles, and calculate the average value.

[0068] The requirements for the solar zenith angle and observation angle during measurement are attached. Figure 2 The instrument's testing angle should be as perpendicular as possible to the angle of sunlight incidence; see attached diagram. Figure 3 Instrument azimuth φ r With the solar azimuth angle φ i The specific relationships are as follows:

[0069] φ i +45<φ r <φ i +135 or φ i -45<φ r <φ i -135.

[0070] Field spectrometer in the attached Figure 3 After measuring M times within the azimuth angle range shown, take the average value as the brightness coefficient of that point. It is recommended that the value of M be between 3 and 6.

[0071] Then, the average brightness coefficients of the target and background within their respective N partitions are weighted by area to obtain the calculated values ​​of the target brightness coefficient and the background brightness coefficient, respectively.

[0072] The area-weighted formula is as follows:

[0073]

[0074] Where r represents the calculated brightness coefficient of the target or background, and S represents the total area of ​​the target or background region. i S represents the brightness coefficient of the i-th partition (the average of multiple measurements from multiple angles). i This represents the area of ​​the i-th partition.

[0075] Finally, the brightness comparison between the target and the background is calculated based on the calculated values ​​of the target brightness coefficient and the background brightness coefficient.

[0076] The formula for calculating brightness contrast is as follows:

[0077]

[0078] Where K represents the brightness contrast, r0 represents the calculated value of the target brightness coefficient, and r b This represents the calculated value of the background brightness coefficient.

[0079] Therefore, by measuring the brightness coefficient of a point multiple times from multiple angles instead of a single measurement, the accuracy of point measurement is improved. Furthermore, by dividing the region into zones using a Y-value map and calculating the average brightness coefficient of the region after area weighting of each measurement point, instead of calculating the average brightness coefficient of randomly selected 30 points within the region, the accuracy of area measurement is improved. This invention is simple and practical, enabling the calculation of brightness comparisons through simple measurements; it is easy to operate and highly accurate.

[0080] Example 2:

[0081] This embodiment provides an apparatus for implementing the target and background brightness comparison measurement method of Embodiment 1, comprising:

[0082] A camera is used to take pictures of the target and the background separately.

[0083] The conversion module is used to convert the RGB values ​​of each pixel in the target photo and the background photo into Y values ​​in the CIE-XYZ spectral tristimulus values, respectively, to obtain the target Y value map and the background Y value map.

[0084] The partitioning module is used to divide the target photo into N partitions based on the target Y-value map, and also to divide the background photo into N partitions based on the background Y-value map.

[0085] A field spectrometer is used to measure the brightness coefficient multiple times from multiple angles at any point selected within each section of the target and background.

[0086] The first calculation module is used to calculate the average value of the brightness coefficient of each selected point in each partition of the target and the background from multiple angles and multiple measurements.

[0087] The second calculation module is used to calculate the target brightness coefficient and the background brightness coefficient by weighting the average brightness coefficients within N zones of both the target and the background by area.

[0088] The third calculation module is used to calculate the brightness comparison between the target and the background based on the calculated values ​​of the target brightness coefficient and the background brightness coefficient.

[0089] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for measuring the brightness contrast between a target and a background, characterized in that, include: Take separate photos of the target and background, and convert the RGB values ​​of each pixel in both photos to Y values ​​in the CIE-XYZ spectral tristimulus values, thus obtaining target Y value maps and background Y value maps. The target is divided into N regions based on the target Y-value map, and the background is divided into N partitions based on the background Y-value map, so that the brightness coefficient of each region after partitioning is approximately the same. Within each zone of both the target and the background, a point is randomly selected, and the brightness coefficient of that point is measured multiple times from multiple angles using a field spectrometer. The average value is then calculated. The average brightness coefficients of the target and background within their respective N partitions are weighted by area to obtain the calculated brightness coefficients for the target and background, respectively. The brightness contrast between the target and the background is calculated based on the target brightness coefficient and the background brightness coefficient. The brightness coefficient of the point was measured multiple times from multiple angles using a field spectrometer, and the average value was calculated. The testing angle of the field spectrometer is perpendicular to the angle of sunlight incidence, and the azimuth angle φ of the field spectrometer is... r With the solar azimuth angle φ i The specific relationships are as follows: f i +45<φ r <φ i +135 orf i -45<φ r <φ i -135.

2. The target and background brightness comparison measurement method according to claim 1, characterized in that, If the main objective is to prevent satellite reconnaissance during the day, the photo should be taken directly above the target and background areas, at noon, with the sun's zenith angle less than 50° and the observation angle less than 10°.

3. The target and background brightness comparison measurement method according to claim 1, characterized in that, The background in the background photo represents the typical optical characteristics of the target area, and the background area is no less than 9 times the size of the target area.

4. The target and background brightness comparison measurement method according to claim 1, characterized in that, N is between 10 and 30.

5. The target and background brightness comparison measurement method according to claim 1, characterized in that, The area weighting is calculated using equation (1): Where r represents the calculated brightness coefficient of the target or background, and S represents the total area of ​​the target or background region. i S represents the average luminance coefficient of the i-th partition. i This represents the area of ​​the i-th partition.

6. The target and background brightness comparison measurement method according to claim 1, characterized in that, The brightness comparison is calculated using equation (2): Where K represents the brightness contrast, r0 represents the calculated value of the target brightness coefficient, and r b This represents the calculated value of the background brightness coefficient.

7. An apparatus for implementing the target-background brightness contrast measurement method as described in any one of claims 1-6, characterized in that, include: A camera is used to take pictures of the target and the background separately. The conversion module is used to convert the RGB values ​​of each pixel in the target photo and the background photo into Y values ​​in the CIE-XYZ spectral tristimulus values, respectively, to obtain the target Y value map and the background Y value map. The segmentation module is used to divide the target image into N regions based on the target Y-value map, and also to divide the background image into N regions based on the background Y-value map, so that the brightness coefficient of each region is approximately the same after segmentation. A field spectrometer is used to measure the brightness coefficient multiple times from multiple angles at any point selected within each section of the target and background. The first calculation module is used to calculate the average value of the brightness coefficient of each selected point in each partition of the target and the background from multiple angles and multiple measurements. The second calculation module is used to calculate the target brightness coefficient and the background brightness coefficient by weighting the average brightness coefficients within N zones of both the target and the background by area. The third calculation module is used to calculate the brightness comparison between the target and the background based on the calculated values ​​of the target brightness coefficient and the background brightness coefficient.

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