Method for correcting cold halo effect of infrared continuous zoom lens

Abstract

The invention belongs to the technical field of infrared image processing, and particularly relates to an infrared continuous zoom lens cold halo effect correction method. According to the method for correcting the cold halo effect of the infrared continuous zoom lens, the whole zoom process of the continuous zoom lens is calibrated, correction templates with different focal lengths are stored, the corresponding correction templates are configured according to the zoom positions, and the method is suitable for imaging with various focal lengths. According to the correction method, calibration and modeling are carried out based on a low-temperature uniform scene; in the zooming process, matched correction parameters are calculated and generated in real time according to the focal length position, and the cold halo effect is removed. The positions of a plurality of focal length points are respectively calibrated according to needs, and the focal length between adjacent calibrated focal length points is realized through neighborhood weighted interpolation. The calculation is simple, real-time and effective. And parameters of the cold halo removing method do not need to be adjusted. Before the infrared camera leaves a factory, the curve template for removing the cold halo effect is calibrated and stored, and parameter adjustment is not needed in the using process of the infrared camera.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared image processing, and in particular relates to a method for correcting cold halo effect of an infrared continuous zoom lens. Background Art

[0002] The cool glow effect is a common optical phenomenon, which is more obvious at the wide-angle end of the camera lens and in low-light environments. This effect is manifested as an unnatural bright light or halo distributed around the center at the edge or corner of the image, making the image look uneven. The causes of the cool glow effect usually include the following aspects: (1) Lens design defects: Some lens designs may cause uneven scattering of light when entering and leaving the lens, especially in the edge area of ​​the lens; the optical coating of the lens may also affect the propagation of light, resulting in the generation of cool glow. (2) Scattering and reflection between optical elements: The optical elements in the lens, such as lenses and aperture blades, may cause light scattering and reflection due to insufficient surface quality, processing accuracy or cleanliness; this scattering and reflection is particularly obvious in wide-angle lenses because the light needs to pass through more optical elements. (3) Lens distortion: Wide-angle lenses usually produce barrel distortion, which will magnify the edge area of ​​the image, thereby enhancing the effect of cool glow; the lens distortion correction algorithm may also affect the generation of cool glow. (4) Environmental factors: In low-light environments, the camera’s automatic gain may increase the overall brightness of the image, thereby amplifying the cold halo effect; light reflections in the surrounding environment may also exacerbate the generation of cold haloes.

[0003] When the infrared imaging module is equipped with a continuous zoom lens, different degrees of cold halo effect often occur during the zoom process. With the optical axis imaging point as the center, it spreads radially in a circle to form concentric circles with uneven brightness of different radii. The brightness of different focal lengths changes with the focal length zoom. The cold halo effect is caused by uneven optical energy of the lens, resulting in uneven energy reception between the center and the surrounding area of ​​the detector, resulting in uneven imaging brightness. It has the following adverse effects on image quality:

[0004] (1) Reduced image uniformity: Cold haloing will produce unnatural bright lights or halos at the edges or corners of the image, destroying the overall uniformity of the image. This makes the image look less natural and affects the viewing experience.

[0005] (2) Loss of detail: Cold halo may obscure or blur details in the image, especially in areas with higher brightness. This will reduce the clarity and resolution of the image and affect image quality.

[0006] (3) Brightness distortion: Cold halo may cause brightness distortion in the image, especially in the edge areas. This makes the brightness of the image look unrealistic and affects the expressiveness.

[0007] (4) Reduced visual effects: Cold halo will reduce the visual effects of the image, especially in scenes that require high clarity and high contrast. This may affect the artistic value and viewing experience of the image.

[0008] (5) Limited professional applications: In some professional fields, such as night vision reconnaissance, aiming, monitoring, identification, tracking, etc., the requirements for image quality are very high. The presence of cold halo may limit the use of images in these fields, especially in scenes that require precise analysis and display.

[0009] Therefore, correcting the cold halo effect has an important impact on improving image quality, enhancing visual effects and professional applications. However, in existing infrared continuous zoom lenses, little consideration is given to eliminating the cold halo effect.

[0010] Patent CN117348220A provides an infrared continuous zoom lens, which relates to the field of optical elements. The infrared continuous zoom lens includes a front fixed group, a zoom group, a compensation group, a rear fixed group and an uncooled long-wave infrared detector from the object side to the image side along the optical axis; wherein the front fixed group includes a first lens with positive optical power; the zoom group includes a second lens with negative optical power and a third lens with negative optical power; the compensation group includes a fourth lens with positive optical power; the rear fixed group includes a fifth lens with negative optical power and a sixth lens with positive optical power; wherein the positions of the zoom group and the compensation group in the direction of the optical axis are adjustable. The infrared continuous zoom lens has an optical structure for realizing continuous zooming, can achieve a high zoom ratio, and has high imaging quality and a smooth zoom cam curve. No correction method for the cold halo effect is proposed.

[0011] Patent CN111650718A proposes an infrared continuous zoom lens and a method for compensating the clarity of an infrared continuous zoom lens. The infrared continuous zoom lens includes a focusing lens group, a zoom lens group, a temperature scale module, a focusing module, and a zoom motor. The focusing lens group and the zoom lens group are stacked in sequence from the object side to the image side to form an optical system. The zoom lens group is connected to the temperature scale module and the zoom motor respectively. The temperature scale module is connected to the focusing module, and the focusing module is connected to the zoom motor. The temperature scale module performs temperature calibration on the infrared continuous zoom lens. The focusing module determines the focusing position according to the temperature calibration of the temperature scale module. The focusing module drives the zoom motor to adjust the lens position of the optical system according to the focusing position. The present invention can perform temperature analysis on the optical system, compensate for the change in imaging quality of the infrared continuous zoom lens caused by temperature change, improve imaging quality, and ensure that the lens is in the best position for clarity. The patent also does not provide a correction method for the cold halo effect.

[0012] To this end, the present invention proposes a method for correcting the cold halo effect of an infrared continuous zoom lens, calibrates the entire zoom process of the continuous zoom lens, saves correction templates of different focal lengths, configures corresponding corrections according to the zoom position, and adapts to imaging at various focal lengths. Summary of the invention

[0013] The invention provides a method for correcting cold halo effect of an infrared continuous zoom lens, which can be used to model and correct the cold halo effect of the infrared continuous zoom lens.

[0014] The cold halo effect correction method of the infrared continuous zoom lens of the present invention is specifically divided into two parts: calibration and correction. The steps are described as follows:

[0015] (1) Divide the focal range of the continuous zoom lens into FocusNum discrete focal point positions according to the step length FocusStep, where FocusMin is the near field focal length and FocusMax is the far field focal length;

[0016] FocusNum=(FocusMax-FocusMin) / FocusStep+1

[0017] (2) Place a low-temperature uniform black body at -20°C to -10°C in front of the continuous zoom lens, turn on the infrared thermal imaging module, and output the infrared original image;

[0018] (3) Adjust the optical axis of the continuous zoom lens to be perpendicular to the imaging focal plane of the infrared sensor and intersect with the focal plane at the imaging center;

[0019] (4) The focal length of the continuous zoom lens is set at FocusNum focal points in sequence, and the low-temperature uniform surface image Img at each position is collected respectively;

[0020] (5) Select the focal point with cold halo effect as the calibration focal point, and use the low-temperature black body uniform surface image to model the cold halo curve Array. That is, for each selected calibration focal point, count the change value of the cold halo effect ring radially diverging from the center of the image Img to the surrounding area, the farthest radius distance to the fixed angle position of the length and width diagonal of the image, the Img image width is ImgWid, and the Img image height is ImgHei; then the length of the cold halo modeling curve is

[0021]

[0022] (6) For each calibrated focal point, the brightness mean GrayMean and variance GrayStd on the current position ring are counted;

[0023] (7) Modeling the cold halo curve, using the variance threshold GrayStdThreshold on the brightness ring to limit it. If GrayStd < GrayStdThreshold, GrayMean is the modeling value of the current radius distance; otherwise, the adjacent qualified modeling value is interpolated as the modeling value of the current radius distance;

[0024] (8) Calculate the mean of the cold halo curve

[0025]

[0026] Among them, i is the loop traversal parameter of the length ArrayLength of the cold halo curve modeling array;

[0027] (9) Subtract the mean from each modeled value to generate the cold halo correction curve for the current focal length

[0028] Array(i)=Array(i)-ArrayMean

[0029] (10) Move to the next focal point position, execute steps (5) to (9), and calibrate the cold light source model curve ArraySet of all focal points;

[0030] (11) In actual usage scenarios, the current focal position is read, and the matching cold halo correction curve is obtained by using the distance weighted summation calculation method based on the focal value in the interval position of the calibrated focal point. Then, the curve is subtracted from the real-time original image to complete the imaging correction of the cold halo effect.

[0031] The cold halo effect correction method of the infrared continuous zoom lens disclosed in the present invention is based on the calibration and modeling of low temperature uniform scenes; during the zoom process, matching correction parameters are calculated and generated in real time according to the focal position to remove the cold halo effect. Multiple focal point positions are set as needed and calibrated separately, and the focal lengths between adjacent calibrated focal points are realized by neighborhood weighted interpolation.

[0032] The beneficial effects of the present invention are:

[0033] (1) Real-time use and simple calculation. When the cold halo effect occurs during the zoom operation of the infrared camera continuous zoom lens disclosed by the present invention, the correction curve is directly calculated and used. The calculation is simple and effective in real time.

[0034] (2) Calibrated in advance, no need to adjust parameters. No need to adjust the parameters of the de-halation effect method. Before the infrared camera leaves the factory, the curve template for de-halation effect is calibrated and stored; no parameter adjustment is required during the use of the infrared camera. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The figure is a flow chart of the method of the present invention.

[0036] Figure 2 This is the cold halo image before correction.

[0037] Figure 3 This is the image after correcting the cold halo. DETAILED DESCRIPTION

[0038] The present invention proposes a method for correcting the cold halo effect of an infrared continuous zoom lens, which can model and correct the cold halo effect of an infrared continuous zoom lens. The specific implementation method is divided into two parts: calibration and correction. The steps are described as follows:

[0039] (1) Divide the focal range of the continuous zoom lens into discrete focal points. For example, the near field focal length FocusMin of a continuous zoom lens is 30 mm, and the far field focal length FocusMax is 210 mm. The focal length change is divided into FocusNum = 19 focal point positions according to a step length FocusStep = 10 mm;

[0040] FocusNum=(FocusMax-FocusMin) / FocusStep+1

[0041] (2) Place a low-temperature uniform black body at -20°C to -10°C in front of the lens, turn on the infrared thermal imaging module, and output the infrared original image;

[0042] (3) Adjust the lens optical axis to be perpendicular to the imaging focal plane of the infrared sensor and intersect with the focal plane at the imaging center.

[0043] (4) The focal length of the lens is set at FocusNum focal point positions in sequence, and the low-temperature uniform surface image Img of each position is collected respectively;

[0044] (5) The focal point position with cold halo effect is used as the calibration focal point, and the cold halo modeling curve Array is performed on its low-temperature uniform surface image. The change value of the cold halo effect ring radially diverging from the center of the image Img is counted, and the farthest radius distance is the fixed angle position of the length and width diagonal of the image. Assuming that the width of the Img image is ImgWid = 1280 pixels and the height is ImgHei = 1024 pixels; then the length of the cold halo modeling curve is

[0045]

[0046] (6) At each calibrated focal point position, the brightness mean GrayMean and variance GrayStd on the current position ring are counted;

[0047] (7) Model the cold halo curve and use the variance threshold GrayStdThreshold on the brightness ring to limit it. If GrayStd < GrayStdThreshold, GrayMean is the modeling value of the current radius distance; otherwise, the adjacent qualified modeling value is interpolated as the modeling value of the current radius distance, with the purpose of discarding the annular aperture with low brightness uniformity.

[0048] (8) Calculate the mean of the cold halo curve

[0049]

[0050] Among them, i is the loop traversal parameter of the length ArrayLength of the cold halo curve modeling array;

[0051] (9) Subtract the mean from each modeled value to generate the cold halo correction curve for the current focal length

[0052] Array(i)=Array(i)-ArrayMean

[0053] (10) Move to the next focal length position, execute steps (5) to (9), and calibrate the cold light source model curve ArraySet of all focal length positions;

[0054] (11) The cold halo model curve is used for correction below;

[0055] (12) Read the current focal length position, and calculate the matching cold halo correction curve according to the focal length value in the calibrated focal length interval using the distance weighted summation calculation method. Then, subtract the curve from the real-time original image to complete the imaging correction of the cold halo effect.

[0056] The present invention provides a method for correcting the cold halo effect of an infrared continuous zoom lens. The method calibrates the entire zoom process of the continuous zoom lens, saves correction templates of different focal lengths, and configures corresponding correction templates according to the zoom position to adapt to various focal length imaging. The correction method of the present invention is based on the calibration and modeling of low temperature uniform scenes; during the zoom process, matching correction parameters are calculated and generated in real time according to the focal length position to remove the cold halo effect.

Claims

1. A method for correcting the cold halo effect of an infrared continuous zoom lens, which is specifically divided into two parts: calibration and correction, and is characterized in that: The steps include: (1) Divide the focal range of the continuous zoom lens into FocusNum discrete focal point positions according to the step length FocusStep, where FocusMin is the near field focal length and FocusMax is the far field focal length; FocusNum=(FocusMax-FocusMin) / FocusStep+1 (2) Place a low-temperature uniform black body at -20°C to -10°C in front of the continuous zoom lens, turn on the infrared thermal imaging module, and output the infrared original image; (3) Adjust the optical axis of the continuous zoom lens to be perpendicular to the imaging focal plane of the infrared sensor and intersect with the focal plane at the imaging center; (4) The focal length of the continuous zoom lens is set at FocusNum focal points in sequence, and the low-temperature uniform surface image Img at each position is collected respectively; (5) Select the focal point with cold halo effect as the calibration focal point, and use the low-temperature black body uniform surface image to model the cold halo curve Array. That is, for each selected calibration focal point, count the change value of the cold halo effect ring radially diverging from the center of the image Img to the surrounding area, the farthest radius distance to the fixed angle position of the length and width diagonal of the image, the Img image width is ImgWid, and the Img image height is ImgHei; then the length of the cold halo modeling curve is (6) For each calibrated focal point, the brightness mean GrayMean and variance GrayStd on the current position ring are counted; (7) Modeling the cold halo curve, using the variance threshold GrayStdThreshold on the brightness ring to limit it. If GrayStd < GrayStdThreshold, GrayMean is the modeling value of the current radius distance; otherwise, the adjacent qualified modeling value is interpolated as the modeling value of the current radius distance; (8) Calculate the mean of the cold halo curve Among them, i is the loop traversal parameter of the length ArrayLength of the cold halo curve modeling array; (9) Subtract the mean from each modeled value to generate the cold halo correction curve for the current focal length Array(i)=Array(i)-ArrayMean (10) Move to the next focal point position, execute steps (5) to (9), and calibrate the cold light source model curve ArraySet of all focal points; (11) In actual usage scenarios, the current focal position is read, and the matching cold halo correction curve is obtained by using the distance weighted summation calculation method based on the focal value in the interval position of the calibrated focal point. Then, the curve is subtracted from the real-time original image to complete the imaging correction of the cold halo effect.

2. The calibration method according to claim 1, characterized in that: In step (1), the step length FocusStep = 10 mm.

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