CN112714300A - Color correction method based on spectral response under ultralow illumination - Google Patents

Color correction method based on spectral response under ultralow illumination Download PDF

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CN112714300A
CN112714300A CN202011384481.2A CN202011384481A CN112714300A CN 112714300 A CN112714300 A CN 112714300A CN 202011384481 A CN202011384481 A CN 202011384481A CN 112714300 A CN112714300 A CN 112714300A
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spectral response
spectrum
camera
response curve
spectral
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CN112714300B (en
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陈佳慧
陈若曦
张雨阳
张旭辉
黄维
宋玉鑫
张俊举
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Nanjing University of Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/646—Circuits for processing colour signals for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/465—Measurement of colour; Colour measuring devices, e.g. colorimeters taking into account the colour perception of the eye; using tristimulus detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors

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  • Spectroscopy & Molecular Physics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Processing Of Color Television Signals (AREA)
  • Color Television Image Signal Generators (AREA)
  • Spectrometry And Color Measurement (AREA)
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Abstract

The invention discloses a color correction method based on spectral response under ultralow illumination, which comprises the following steps: acquiring a daylight spectrum in the day and a night light spectrum at night by using a spectrometer; acquiring a spectral response curve of a camera by using a monochromator and a spectrometer; calculating the integral of the daily spectrum and the spectral response curve and the integral of the night light spectrum and the spectral response curve; and respectively calculating the correction values of the RGB three-channel values according to the integration result to obtain the image after color correction. The invention can finish the spectrum correction of the image only by knowing the spectrum response curve of the camera and the spectrum curve that the acquired image is night light, and the required information amount is small.

Description

Color correction method based on spectral response under ultralow illumination
Technical Field
The invention belongs to the field of computer vision, and particularly relates to a color correction method based on spectral response under ultralow illumination.
Background
Under the condition of weak light, human eyes gradually lose the resolving power of colors, and even images of scenes cannot be obtained due to the reduction of sensitivity. The ultra-low illumination color restoration technology is characterized in that the characteristic that human eyes have higher resolution on color vision is utilized, and an image acquired under weak illumination is processed into a color image suitable for human eyes to observe, so that the performance of a night vision system and the observation effect of a night vision image are improved, and an observer can acquire more effective information. The method is based on the visual characteristics of human eyes, and a color correction algorithm under the ultra-low illumination is researched according to the change of an environment spectrum.
Based on the color vision principle of human eyes, the human eyes have three different cone-shaped photosensitive cells which respectively only generate visual reflection to the stimulation of the energy of red, green and blue spectrums. When the same object is illuminated by light sources with different energy spectral distributions, the colors seen are different. The difference of spectral distribution characteristics of sunlight, moonlight and starlight, and the difference of spectral curves of sunlight, moonlight and starlight should be an important reason why the color reduction capability of the CMOS imaging device is reduced at low illumination.
The true-color low-light-level image has the defects of low color reduction degree, high noise, large influence of colors on the environment and the like, and the existing color correction method cannot completely meet the requirement of color correction of the true-color low-light-level image. The automatic white balance method is greatly influenced by illumination and is easy to generate larger deviation; the gray world method is limited by scene colors and cannot be used for all scenes; the color correction method based on Retinex algorithm can generate large image noise and is not suitable for true-color low-light level images.
Disclosure of Invention
The invention aims to provide a color correction method based on spectral response under ultralow illumination.
The technical scheme for realizing the purpose of the invention is as follows: a color correction method based on spectral response under ultralow illumination comprises the following steps:
step 1: acquiring a daylight spectrum in the day and a night light spectrum at night by using a spectrometer;
step 2, acquiring a spectral response curve of the camera by using a monochromator and a spectrometer;
step 3, calculating the integral of the daily spectrum and the spectral response curve and the integral of the night light spectrum and the spectral response curve;
and 4, respectively calculating the correction values of the RGB three-channel values according to the integral result to obtain the color-corrected image.
Preferably, the specific steps of acquiring the spectral response curve of the camera by using the monochromator and the spectrometer are as follows:
aligning the light outlet of the integrating sphere with the light inlet of the monochromator, and aligning the true color camera with the light outlet of the monochromator;
adjusting the wavelength of a monochromator to a set initial value, setting a step length, and sequentially recording imaging data of a camera detector until a set final wavelength value is reached;
determining RGB values of the picture in different wave bands, and calculating a spectral response curve of the camera according to tristimulus values at different wavelengths and a spectral curve of the light source.
Preferably, the integral of the daily spectrum and the spectral response curve is calculated, and the specific formula of the integral of the night light spectrum and the spectral response curve is as follows:
er＝∫Pr(λ)Sr(λ)dλ
eg＝∫Pg(λ)Sg(λ)dλ
eb＝∫Pb(λ)Sb(λ)dλ
in the formula, Sr(λ)、Sg(λ)、Sb(λ) respectively represents the spectral sensitivity response characteristics, P, of the RGB three channels of the camerar(λ)、Pg(λ)、Pb(λ) is the RGB three-channel power spectrum distribution of daylight/night-day light.
Preferably, the calculation formula of the correction value of the RGB three-channel values is:
R′＝R*(edr/enr)
G′＝G*(edg/eng)
B′＝B*(edb/enb)
c＝R′+G′+B′
in the formula, edr、edg、edbAs a result of integration of the daytime spectrum with the spectral response curve of the camera, enr、eng、enbR, G, B is the integration result of the night spectrum and the camera spectrum response curve, and R ', G ' and B ' are the corrected RGB three-channel pixel values.
Compared with the prior art, the invention has the following remarkable advantages: (1) the invention has good prospect in the field of color low-light night vision; (2) the invention can finish the spectrum correction of the image only by knowing the spectrum response curve of the camera and acquiring the spectrum curve that the image is night sky light, and the required information amount is less; (3) the invention has small calculated amount and good real-time property.
The present invention is described in further detail below with reference to the attached drawing figures.
Drawings
FIG. 1 is a flow chart of a color correction method based on spectral response under ultra-low illumination.
Fig. 2 is an unprocessed night-day image captured by a true color camera.
Fig. 3 is a graph of the spectrum during the day.
Fig. 4 is a spectral curve of night sky light.
Fig. 5 is a spectral response curve of a camera.
Fig. 6 is an image corrected using the present invention.
Detailed Description
As shown in fig. 1, a color correction method based on spectral response under ultra-low illumination includes the following steps:
step 1, acquiring a daylight spectrum in the day and a night light spectrum at night by using a spectrometer.
Step 2, acquiring a spectral response curve of the camera by using a monochromator and a spectrometer;
in one embodiment, a spectrometer is used to measure the spectral curve of an integrating sphere light source;
aligning the light outlet of the integrating sphere with the light inlet of the monochromator, and aligning the true color camera with the light outlet of the monochromator;
and adjusting the wavelength of the monochromator to 380nm, setting the step length to be 10nm, and sequentially recording imaging data of the camera detector until the wavelength reaches 800 nm.
Determining RGB values of the picture in different wave bands, and calculating a spectral response curve of the camera according to tristimulus values at different wavelengths and a spectral curve of the light source.
Step 3, calculating the integral of the daily spectrum and the spectral response curve and the integral of the night light spectrum and the spectral response curve, wherein the specific calculation formula is as follows:
er＝∫Pr(λ)Sr(λ)dλ
eg＝∫Pg(λ)Sg(λ)dλ
eb＝∫Pb(λ)Sb(λ)dλ
in the formula, Sr(λ)、Sg(λ)、Sb(λ) respectively represents the spectral sensitivity response characteristics, P, of the RGB three channels of the camerar(λ)、Pg(λ)、Pb(lambda) is the RGB three-channel power spectrum distribution of sunlight/night sky light, er、eg、ebThe color of the image in the camera is represented by e, which is the integral of the spectral response of each color channel of the camera in the visible ranger、eg、ebThe sum of the three is the color distribution of the image.
And 4, respectively calculating correction values of RGB three-channel values according to the integration result in the step 3 to finish the color correction of the image, wherein the specific formula is as follows:
R′＝R*(edr/enr)
G′＝G*(edg/eng)
B′＝B*(edb/enb)
c＝R′+G′+B′
edr、edg、edbas a result of integration of the daytime spectrum with the spectral response curve of the camera, enr、eng、enbR, G, B is the integration result of the night spectrum and the camera spectrum response curve, and R ', G ' and B ' are the corrected RGB three-channel pixel values.
And synthesizing the color corrected image according to the corrected pixel values of the RGB three channels.
The invention can carry out color correction on the true-color low-light-level night vision image collected under ultralow illumination, so that the color of the night-day image of the scene is closer to the color of the scene under sunlight, the color observation rule of human eyes is better met, the color of the night-day image is similar to the color of the image scene commonly used in computer vision, and the subsequent target identification and target detection are facilitated.

Claims (4)

1.一种超低照度下基于光谱响应的色彩校正方法，其特征在于，包括以下步骤：1. a color correction method based on spectral response under an ultra-low illuminance, is characterized in that, comprises the following steps: 步骤1：利用光谱仪获取白天的日光光谱和夜晚的夜天光光谱；Step 1: Use a spectrometer to obtain the daylight spectrum during the day and the night sky light spectrum at night; 步骤2：利用单色仪和光谱仪获取相机的光谱响应曲线；Step 2: Use a monochromator and a spectrometer to obtain the spectral response curve of the camera; 步骤3：计算日天光谱与光谱响应曲线的积分，夜天光光谱光谱与光谱响应曲线的积分；Step 3: Calculate the integral of the day-sky spectrum and the spectral response curve, and the integral of the night-sky light spectral spectrum and the spectral response curve; 步骤4：根据积分结果，分别计算RGB三通道值的校正值，得到色彩校正后的图像。Step 4: According to the integration results, the correction values of the RGB three-channel values are calculated respectively to obtain a color-corrected image. 2.根据权利要求1所述的超低照度下基于光谱响应的色彩校正方法，其特征在于，利用单色仪和光谱仪获取相机的光谱响应曲线的具体步骤为：2. the color correction method based on spectral response under ultra-low illumination according to claim 1, is characterized in that, utilizes monochromator and spectrometer to obtain the concrete steps of the spectral response curve of camera as: 将积分球出光口对准单色仪进光口，真彩相机对准单色仪出光口；Align the light outlet of the integrating sphere with the light inlet of the monochromator, and the true color camera to the light outlet of the monochromator; 将单色仪波长调到设定的初始值，设置步长，依次记录相机探测器的成像数据，直至到设定的波长终值；Adjust the wavelength of the monochromator to the set initial value, set the step size, and record the imaging data of the camera detector in turn until the set wavelength final value is reached; 确定图片在不同波段的RGB值，通过不同波长处的三刺激值及光源的光谱曲线，计算出相机的光谱响应曲线。Determine the RGB values of the image in different bands, and calculate the spectral response curve of the camera through the tristimulus values at different wavelengths and the spectral curve of the light source. 3.根据权利要求1所述的超低照度下基于光谱响应的色彩校正方法，其特征在于，计算日天光谱与光谱响应曲线的积分，夜天光光谱光谱与光谱响应曲线的积分的具体公式为：3. the color correction method based on spectral response under the ultra-low illumination according to claim 1, is characterized in that, calculates the integral of daytime spectrum and spectral response curve, the concrete formula of the integral of night sky light spectrum spectrum and spectral response curve is: : er＝∫Pr(λ)Sr(λ)dλe r =∫P r (λ)S r (λ)dλ eg＝∫Pg(λ)Sg(λ)dλe g =∫P g (λ)S g (λ)dλ eb＝∫Pb(λ)Sb(λ)dλe b =∫P b (λ)S b (λ)dλ 式中，Sr(λ)、Sg(λ)、Sb(λ)分别表示相机RGB三通道的光谱灵敏度响应特性，Pr(λ)、Pg(λ)、Pb(λ)为日光/夜天光的RGB三通道功率频谱分布。In the formula, S r (λ), S g (λ), and S b (λ) represent the spectral sensitivity response characteristics of the three RGB channels of the camera, respectively, and P r (λ), P g (λ), and P b (λ) are: RGB three-channel power spectral distribution of daylight/night sky light. 4.根据权利要求1所述的超低照度下基于光谱响应的色彩校正方法，其特征在于，RGB三通道值的校正值的计算公式为：4. the color correction method based on spectral response under the ultra-low illumination according to claim 1, is characterized in that, the calculation formula of the correction value of RGB three-channel value is: R′＝R*(edr/enr)R′=R*(e dr /e nr ) G′＝G*(edg/eng)G′=G*(e dg /e ng ) B′＝B*(edb/enb)B'=B*(e db / enb ) c＝R′+G′+B′c=R'+G'+B' 式中，edr、edg、edb为白天光谱与相机光谱响应曲线的积分结果，enr、eng、enb为夜天光谱与相机光谱响应曲线的积分结果，R、G、B为图像的RGB三通道像素值，R′、G′、B′为校正后的RGB三通道的像素值。In the formula, e dr , edg , and e db are the integration results of the daytime spectrum and the camera’s spectral response curve, enr , e ng , and e nb are the integration results of the night sky spectrum and the camera’s spectral response curve, R, G, and B are RGB three-channel pixel values of the image, R', G', B' are the corrected RGB three-channel pixel values.
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Patent Citations (4)

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CN107170013A (en) * 2017-05-03 2017-09-15 北京理工大学 A kind of scaling method of RGB camera spectral response curve
CN107197225A (en) * 2017-06-13 2017-09-22 浙江大学 Color digital camera white balance correcting based on chromatic adaptation model
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项金蓉等: "基于光谱可调积分球光源的多光谱相机颜色校正研究", 《激光与光电子学进展》 *

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