CN105812661B - A kind of digital camera uniformity correcting method based on light box and gray card - Google Patents

A kind of digital camera uniformity correcting method based on light box and gray card Download PDF

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CN105812661B
CN105812661B CN201610150471.XA CN201610150471A CN105812661B CN 105812661 B CN105812661 B CN 105812661B CN 201610150471 A CN201610150471 A CN 201610150471A CN 105812661 B CN105812661 B CN 105812661B
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digital camera
light source
gray card
camera
uniformity
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CN105812661A (en
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徐海松
方竞宇
汪哲弘
吴晓玟
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Zhejiang University ZJU
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/60Control of cameras or camera modules
    • H04N23/68Control of cameras or camera modules for stable pick-up of the scene, e.g. compensating for camera body vibrations
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N17/00Diagnosis, testing or measuring for television systems or their details
    • H04N17/002Diagnosis, testing or measuring for television systems or their details for television cameras
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/10Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths
    • H04N23/13Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths with multiple sensors
    • H04N23/16Optical arrangements associated therewith, e.g. for beam-splitting or for colour correction

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Biomedical Technology (AREA)
  • General Health & Medical Sciences (AREA)
  • Color Television Image Signal Generators (AREA)

Abstract

The invention discloses a kind of digital camera uniformity correcting method based on light box and gray card.Standard gray card is positioned in light box by this method, translates the image for obtaining standard color card by way of camera is repeatedly shot in image different location vertical optical axis, homogeneity correction coefficient is mathematically obtained finally by difference or fitting.The method of the present invention exchanges the spatially uniform of light source for the time stability of light source, overcome traditional digital cameras uniformity test and correction must be in the limitation using such as integrating sphere uniform source system, the scope of application for considerably increasing test and correcting digital camera imaging uniformity, also avoid as metamerism phenomenon that color filter type integrating sphere light source generates and caused by measurement error.

Description

一种基于标准灯箱和灰卡的数码相机均匀性校正方法A digital camera uniformity correction method based on standard light box and gray card

技术领域technical field

本发明涉及到光学成像、数字图像处理领域,尤其涉及一种基于标准灯箱和灰卡替代积分球等特殊均匀光源装置的数码相机成像均匀性校正的方法。The invention relates to the fields of optical imaging and digital image processing, in particular to a method for correcting digital camera imaging uniformity based on special uniform light source devices such as a standard light box and a gray card instead of an integrating sphere.

背景技术Background technique

目前,数码相机得到了广泛的应用,不仅被用于拍摄图像记录风景,也在科学研究领域用作成像式的测色设备。但是数码相机成像并不完美,其中一个典型的成像现象就是成像的非均匀性。由于镜头的渐晕光阑、轴外像点的余弦暗角(轴外像点的光照度随视场角余弦的四次方而降低)、成像元件(如CCD或者CMOS)本身的非均匀性等多种因素的共同作用,相机对于一个亮度均匀的物体所成像最终呈现出非均匀的特性。这种成像非均匀现象也常常被称为阴影(shading)。At present, digital cameras have been widely used, not only for shooting images to record scenery, but also for imaging color measurement equipment in the field of scientific research. However, the imaging of digital cameras is not perfect, and one of the typical imaging phenomena is the non-uniformity of imaging. Due to the vignetting diaphragm of the lens, the cosine vignetting of the off-axis image point (the illuminance of the off-axis image point decreases with the fourth power of the cosine of the field angle), the non-uniformity of the imaging element (such as CCD or CMOS) itself, etc. Due to the combined effect of various factors, the camera's imaging of an object with uniform brightness will eventually show non-uniform characteristics. This imaging non-uniformity is also often referred to as shading.

ISO 17957对数码相机成像的阴影测量条件作了推荐:需要一个均匀的场目标,可以代表三种常见照明环境的光源,即平均室外日光、室内白炽照明和室内荧光灯照明。为了产生符合要求的测试条件,需要专门搭建用于测试阴影的照明环境。业界通常使用积分球均匀光源系统以提供均匀的光照条件。一方面,这样的测试条件和方法极大的限制了数码相机均匀性测试和校正的测试场合,为实际测量和校正带来不便,尤其是对于使用广角镜头的数码相机,要提供一个足够大面积的均匀光照更是困难。另一方面,要实现ISO规定的三种典型光源,目前积分球往往采用白炽灯和滤光片组合的方式来产生不同类型的光源,这样的光源只能保证色温的准确,却会因同色异谱而造成潜在的测量不准确的风险。ISO 17957 recommends shadow measurement conditions for digital camera imaging: A uniform field target is required that can represent light sources for three common lighting environments, namely, average outdoor daylight, indoor incandescent lighting, and indoor fluorescent lighting. In order to generate the required test conditions, a lighting environment specifically set up for testing shadows is required. The industry usually uses an integrating sphere uniform light source system to provide uniform lighting conditions. On the one hand, such test conditions and methods greatly limit the test occasions for digital camera uniformity test and correction, which brings inconvenience to actual measurement and correction, especially for digital cameras with wide-angle lenses, it is necessary to provide a large enough area Uniform lighting is even more difficult. On the other hand, in order to realize the three typical light sources specified by ISO, currently integrating spheres often use the combination of incandescent lamps and filters to produce different types of light sources. Spectrum causing potential risk of measurement inaccuracy.

发明内容Contents of the invention

为了克服现有数码相机成像均匀性的测试校正方法中需要使用特殊均匀光源装置的不便,本发明提供一种使用标准灯箱和标准灰卡,对数码相机的成像均匀性进行测试和校正的方法。In order to overcome the inconvenience of using a special uniform light source device in the existing digital camera imaging uniformity testing and calibration method, the present invention provides a method for testing and calibrating the digital camera imaging uniformity using a standard light box and a standard gray card.

本发明的目的是通过以下技术方案来实现的:一种基于标准灯箱和灰卡的数码相机均匀性校正方法,该方法包括以下步骤:The object of the present invention is achieved by the following technical solutions: a digital camera uniformity correction method based on a standard light box and a gray card, the method may further comprise the steps:

(1)布置灯箱,放置灰卡:将灯箱放置于暗室中,将灰卡放置于灯箱中,灰卡与灯箱底面成固定角度。(1) Arrange the light box and place the gray card: place the light box in the dark room, place the gray card in the light box, the gray card and the bottom surface of the light box form a fixed angle.

(2)打开灯箱的一种光源,对光源进行预热。(2) Turn on a light source of the light box to preheat the light source.

(3)相机位置及参数设置:待灯箱光源预热完毕,将数码相机放置于灰卡可正常对焦的距离处,数码相机光轴垂直于灰卡平面,设置并固定数码相机拍摄参数,使得数码相机对灰卡曝光正确;所述数码相机拍摄参数包括ISO感光度、光圈、快门和焦距。(3) Camera position and parameter setting: After the light box light source is preheated, place the digital camera at a distance where the gray card can focus normally. The optical axis of the digital camera is perpendicular to the plane of the gray card. The exposure of the camera to the gray card is correct; the shooting parameters of the digital camera include ISO sensitivity, aperture, shutter speed and focal length.

(4)相机拍摄:将数码相机在垂直于光轴平面上平移并拍摄,使得N次拍摄得到的灰卡尽可能的散布出现在图像的各个位置;提取第i张图片中灰卡光照均匀区域的RGB值的平均值RGBi,以及该区域的中心位置qi,i=1,2,...,N。(4) Camera shooting: Translate and shoot the digital camera on a plane perpendicular to the optical axis, so that the gray cards obtained from N times of shooting are scattered and appear in various positions of the image as much as possible; extract the evenly illuminated area of the gray card in the i-th picture The average value RGB i of the RGB values of , and the center position q i of the area, i=1,2,...,N.

(5)预测并校正相机的均匀性:根据步骤(4)获得的位置变量qi和图像响应值RGBi,通过插值或者拟合得到从位置变量qi映射到图像响应值RGBi的预测函数f(·),对于图像P中的任意一点p,得到该点均匀性校正系数k(p):(5) Predict and correct the uniformity of the camera: According to the position variable q i and the image response value RGB i obtained in step (4), the prediction function mapped from the position variable q i to the image response value RGB i is obtained by interpolation or fitting f( ), for any point p in the image P, the uniformity correction coefficient k(p) of the point is obtained:

(6)更换灯箱的光源种类,重复步骤(2)~(5),直至所有种类光源测试完毕,得到该数码相机针对每种光源的均匀性校正系数。(6) Change the light source type of the light box, repeat steps (2) to (5), until all types of light sources are tested, and obtain the uniformity correction coefficient of the digital camera for each light source.

本发明的有益效果是:本发明使用标准灯箱和标准灰卡,采用多次平移相机拍摄同一标准色卡的方式,通过插值拟合的数学方法,得到图像的均匀性校正系数。本方法以光源的时间稳定性换取光源的空间均匀性,克服传统数码相机均匀性测试和校正必须在使用诸如积分球均匀光源系统的局限,大大增加了测试和校正数码相机成像均匀性的适用范围。The beneficial effects of the present invention are: the present invention uses a standard light box and a standard gray card, adopts the method of shifting the camera multiple times to shoot the same standard color card, and obtains the uniformity correction coefficient of the image through the mathematical method of interpolation and fitting. This method trades the temporal stability of the light source for the spatial uniformity of the light source, overcomes the limitation that the traditional digital camera uniformity test and correction must use a uniform light source system such as an integrating sphere, and greatly increases the scope of application for testing and correcting digital camera imaging uniformity .

附图说明Description of drawings

图1是数码相机成像均匀性测试和校正的流程图;Figure 1 is a flow chart of digital camera imaging uniformity testing and correction;

图2是测试实验装置图;Fig. 2 is a test experimental device diagram;

图3是实例中拍摄的标准灰卡图片;Figure 3 is a standard gray card picture taken in the example;

图4是积分球方法和本发明方法的测试结果比较图,(a)为采用A光源,(b)为采用D65光源。Fig. 4 is the test result comparison chart of integrating sphere method and the method of the present invention, (a) adopts A light source, (b) adopts D65 light source.

具体实施方式Detailed ways

下面以尼康数码单反相机D3x配尼康AF-S尼克尔24-120mm f/4G ED VR镜头、GretagMacbeth Spectralight III标准灯箱和X-rite ColorChecker Passport中的灰卡为例,阐述测试和校正这台数码相机的成像均匀性的具体步骤。需说明的是,本发明不限于尼康数码单反相机,只要能获取到图像数字格式输出的数码相机均适用于本发明,也不限于GretagMacbeth标准灯箱或者X-rite色卡,只要能提供稳定光源和包含光谱中性色块的色卡均适用于本发明。The following takes Nikon digital SLR camera D3x with Nikon AF-S NIKKOR 24-120mm f/4G ED VR lens, GretagMacbeth Spectralight III standard light box and gray card in X-rite ColorChecker Passport as an example to illustrate the testing and calibration of this digital camera Specific steps for imaging uniformity. It should be noted that the present invention is not limited to Nikon digital SLR cameras, as long as digital cameras that can obtain image digital format output are applicable to the present invention, and are not limited to GretagMacbeth standard light boxes or X-rite color cards, as long as they can provide stable light sources and Color cards containing spectrally neutral color patches are all suitable for the present invention.

如图1所示,本发明提供的一种基于标准灯箱和灰卡的数码相机均匀性校正方法,包括以下步骤:As shown in Figure 1, a kind of digital camera uniformity correction method based on standard light box and gray card provided by the present invention comprises the following steps:

(1)布置灯箱,放置灰卡:如图2所示,将Spectralight III标准灯箱放置于暗室中,将X-rite ColorChecker Passport色卡翻至白平衡目标页(即中性灰页),放置于灯箱中,灰卡与灯箱底面成45角度以便相机捕获图像。(1) Lay out the light box and place the gray card: As shown in Figure 2, place the Spectralight III standard light box in a dark room, turn the X-rite ColorChecker Passport color card to the white balance target page (neutral gray page), and place it on the In the light box, the gray card is at a 45 angle to the bottom of the light box for the camera to capture the image.

(2)选择光源:从Spectralight III标准灯箱中选择D65光源,打开预热。(2) Select the light source: choose the D65 light source from the Spectralight III standard light box, and turn on the preheating.

(3)相机位置及参数设置:待步骤(2)的灯箱光源预热完毕,将D3x数码相机放置于灰卡可正常对焦的距离2.0m处,相机光轴尽量垂直于灰卡平面,设置并固定相机拍摄参数,ISO感光度200、光圈数为4、快门1/80s、焦距50mm,使得数码相机对灰卡曝光正确(Ev=0)。(3) Camera position and parameter setting: After the preheating of the light box light source in step (2), place the D3x digital camera at a distance of 2.0m where the gray card can focus normally. The shooting parameters of the camera were fixed, ISO sensitivity was 200, aperture number was 4, shutter speed was 1/80s, and focal length was 50mm, so that the exposure of the digital camera to the gray card was correct (Ev=0).

(4)相机拍摄:将相机在垂直于光轴平面上从左至右从上至下平移(轴向的位移造成的理论误差仅为fΔr/[r(f+r)]×100%,其中r为物距,f为相机焦距,Δr为轴向位移差,Δr单位为mm。本实施例中轴向的位移造成的理论误差仅为Δr/82000×100%),使得40次拍摄得到的灰卡尽可能的散布出现在图像的各个位置。提取第i张图片中灰卡光照均匀区域的RGB值的平均值,记为RGBi,以及该区域的中心位置,记为qi,i=1,2,...,40。(4) Camera shooting: translate the camera from left to right and from top to bottom on a plane perpendicular to the optical axis (the theoretical error caused by axial displacement is only fΔr/[r(f+r)]×100%, where r is the object distance, f is the focal length of the camera, Δr is the axial displacement difference, and the unit of Δr is mm. The theoretical error caused by the axial displacement in this embodiment is only Δr/82000×100%), so that the obtained 40 shots Gray cards appear scattered throughout the image as much as possible. Extract the average value of the RGB values of the uniformly illuminated area of the gray card in the i-th picture, denoted as RGB i , and the center position of the area, denoted as q i , where i=1,2,...,40.

(5)预测并校正相机的均匀性:根据步骤(4)获得的位置变量qi和图像响应值RGBi,i=1,2,...,40,通过二维立方插值法得到从位置变量qi映射到图像响应值RGBi的预测函数f(·),对于图像P中的任意一点p,得到该点均匀性校正系数k(p):(5) Predict and correct the uniformity of the camera: according to the position variable qi obtained in step (4) and the image response value RGB i , i=1,2,...,40, the position variable is obtained by the two-dimensional cubic interpolation method q i is mapped to the prediction function f(·) of the image response value RGB i , for any point p in the image P, the uniformity correction coefficient k(p) of this point is obtained:

式中,max(·)为求最大值函数。In the formula, max( ) is the function for finding the maximum value.

(6)Spectralight III标准灯箱更换至A光源,重复(2)~(5)步骤,得到该数码相机针对多种光源的均匀性校正系数。(6) Replace the Spectralight III standard light box with light source A, and repeat steps (2) to (5) to obtain the uniformity correction coefficients of the digital camera for various light sources.

实验结果以绿色通道(G通道)为例,如图4所示,本发明方法的实验结果和积分球均匀光源系统下得到的校正系数非常接近。The experimental results take the green channel (G channel) as an example, as shown in Figure 4, the experimental results of the method of the present invention are very close to the correction coefficient obtained under the uniform light source system of the integrating sphere.

Claims (1)

1. a kind of digital camera uniformity correcting method based on light box and gray card, which is characterized in that this method include with Lower step:
(1) it arranges lamp box, places gray card:Lamp box is positioned in darkroom, gray card is positioned in lamp box, gray card and lamp box bottom surface At fixed angle;
(2) a kind of light source for opening lamp box, preheats light source;
(3) camera position and parameter setting:It waits for that lamphouse light source preheating finishes, digital camera is positioned over what gray card can normally focus At distance, digital camera optical axis is arranged perpendicular to gray card plane and fixes digital camera acquisition parameter so that digital camera is to ash Exposed card is correct;The digital camera acquisition parameters include ISO sensitivity, aperture, shutter and focal length;
(4) camera is shot:Digital camera is being translated and shot on optical axial plane so that the gray card that n times are shot The each position for appearing in image is spread as far as possible;Extract the average RGB responses in gray card uniform illumination region in the i-th pictures Value RGBiAnd the center q in the regioni, i=1,2 ..., N;
(5) uniformity of prediction and correcting camera:The location variable q obtained according to step (4)iWith average RGB responses RGBi, It is obtained from location variable q by interpolation or fittingiIt is mapped to average RGB responses RGBiAnticipation function f (), for figure As any point p in P, the homogeneity correction coefficient k (p) is obtained:
(6) the light source type for replacing lamp box, repeats step (2)~(5), until all kinds test of light source finishes, obtains the number Code camera is directed to the homogeneity correction coefficient of each light source.
CN201610150471.XA 2016-03-16 2016-03-16 A kind of digital camera uniformity correcting method based on light box and gray card Expired - Fee Related CN105812661B (en)

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CN108120680B (en) * 2017-12-19 2019-11-22 清华大学 Method and device for removing stray light in microscopic imaging based on prior photoelectric characteristics
CN109889823B (en) * 2019-04-08 2021-02-26 苏州莱测检测科技有限公司 Detection method for detecting performance of stereoscopic vision imaging equipment
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