CN104902153B - A kind of multispectral camera color correcting method - Google Patents

Abstract

The invention relates to a color correction method for a multi-spectral camera. The optical path system of the invention is composed of an integrating sphere light source, a transmissive 24-color standard color plate, a light baffle with holes, a collimator, and a spectroradiometer. The light beam emitted by the integrating sphere light source passes through the color block of the transmission type 24-color standard color plate and the light baffle plate with openings, reaches the focal plane of the collimator, collimates through the collimator, and enters the spectroradiometer to obtain the original data. The invention realizes the color correction of various types and calibers of linear array CCD aerospace remote sensing multispectral cameras and large field of view and long focal length area array multispectral cameras.

Description

A Color Correction Method for Multispectral Camera

technical field

The invention relates to a multispectral camera color correction method, which can be widely used in the field of aerospace remote sensing.

Background technique

Multispectral cameras are used more and more widely in the field of aerospace remote sensing. With the increasing requirements for high resolution and high performance of remote sensors, large aperture, long focal length line array cameras and large field of view long focal length area array multispectral cameras are becoming more and more important in the field of aerospace remote sensing.

The spectral band setting of the multi-spectral camera is generally four spectral bands of red, green, blue and near-infrared, and the red, green and blue spectral bands are respectively named as B1, B2, and B3 spectral bands. True-color remote sensing images are composed of red, green, and blue spectral bands, and the color of the subject is displayed as faithfully as possible. True color remote sensing images provide more information than grayscale images. Due to the constraints of light source, atmosphere, and remote sensing camera itself, the obtained color remote sensing images do not reproduce the color of real objects as expected, and there is a certain degree of color shift. Seriously affect the reliability and effectiveness of data expression information. The traditional remote sensing image processing is to perform radiometric correction for each band in the laboratory and in flight. This kind of radiometric correction increases the complexity of the remote sensing camera. In addition, the radiometric correction is very accurate for neutral color correction, but it has a large error for color .

The current method of color correction for commercial area-scan digital cameras in China is to use a standard light box based on "D65 light source + reflective standard color palette". The area array digital camera images the reflective standard color plate in the standard light box by focusing, reads the RGB value of the corresponding color block in the image, and establishes a relationship with the standard chromaticity value of the corresponding color block of the standard color plate in the standard light box. A mutual conversion lookup table, which can be used to map a certain point of the RGB file captured by the digital camera to the corresponding chromaticity space, and then perform color correction on the captured pictures in real time. Some short focal length area array remote sensing cameras also adopt similar color correction methods.

Due to the imaging mode and focal length of the linear array aerospace remote sensing multispectral camera and the large field of view long focal length area aerial remote sensing multispectral camera, the standard color plate test distance is required to be relatively large, and the test work cannot be completed in the laboratory. The method of imaging test with standard color plates is no longer applicable; considering the performance requirements of camera aperture, field of view and focal length, it is difficult and expensive to make large-caliber monochrome standard plates of different colors, and this method is not feasible . In addition, there are many parameters that can be set for each multi-spectral spectrum band of this type of remote sensing camera, which will lead to changes in the output DN value of the corresponding spectrum band, causing great difficulties in color correction. The above-mentioned similar problems also exist for large field of view and long focal length area array multispectral cameras.

Contents of the invention

The technical problem solved by the present invention is to overcome the deficiencies of the prior art and provide a multi-spectral camera color correction method to ensure the accuracy and stability of the final color correction.

The technical solution of the present invention is: a multi-spectral camera color correction method, the system involved includes an integrating sphere light source, a transmissive 24-color standard color plate, a light baffle with holes, a collimator, and a spectroradiometer; the integrating sphere light source The outgoing beam passes through the color blocks on the transmissive 24-color standard color plate and the light baffle plate with openings, reaches the focal plane of the collimator, collimates through the collimator, and then enters the measured multispectral camera or spectroradiometer. Then obtain the original data and images; the size of the opening on the light shielding plate with openings is consistent with the size of a color block on the transmissive 24-color standard color plate; the steps are as follows:

1) The light emitted by the integrating sphere light source is collimated by the collimator to generate parallel light;

2) After setting up the multispectral camera under test at the light outlet of the collimator, adjust the height, pitch angle and azimuth of the multispectral camera under test so that the color block A on the transmissive 24-color standard color board is in the same position as the multispectral camera under test. The above image; the color block A is the color block with the second highest transmittance among the gray color blocks on the transmission type 24-color standard color plate; adjust the output power of the integrating sphere light source, so that each spectral segment of the measured multispectral camera is in the In the linear response region, and fix the output power of the integrating sphere light source;

3) Remove the multi-spectral camera to be measured, set up the spectroradiometer behind the light outlet of the collimator; adjust the height, elevation angle and azimuth of the spectroradiometer so that the spectroradiometer is coaxial with the collimator;

4) Adjust the positions of the different color blocks on the transmissive 24-color standard swatch, and use a spectroradiometer to collect the spectral radiance corresponding to each color block on the transmissive 24-color standard swatch and the chromaticity coordinates under the CIE-xyz coordinate system;

5) Establish the relational equation of the color correction coefficient, the equivalent radiance of the multispectral camera, and the R, G, and B values after the color synthesis of the multispectral spectrum segment, and calculate and obtain the color correction coefficient; the relational equation is as follows:

Among them, L _B1 ~ L _B3 is the equivalent radiance of a certain color block area of the transmissive 24-color standard swatch received by the multi-spectral camera under test; is the multi-spectral camera color correction coefficient matrix; R, G, and B are the final R, G, and B component values after the color synthesis of each spectral segment;

The calculation process of L _B1 ~ L _B3 in step 5) is:

Among them, L(λ) is the spectral radiance data of the emitted light from the collimator calibrated by the spectroradiometer; R _Bi (λ) is the relative spectral response curve of the Bi band of the measured multispectral camera.

The calculation process of R, G, B in the step 5) is:

in x, y, z are the chromaticity coordinates under the CIE-xyz coordinate system.

The beneficial effect of the present invention compared with prior art:

(1) For the first time, the method of "transmissive 24-color standard color plate + collimator" is used to realize the color correction of the aerospace remote sensing multispectral camera. It solves the problems of long focal length, large field of view aerospace remote sensing camera color calibration, large test distance, large-caliber reflective standard color plate processing technology difficulty and high cost.

(2) In the establishment of the data processing model, the relationship between the final R, G, and B component values after the color synthesis of the multispectral camera bands and the camera input equivalent radiance of the bands B1 to B3 is established, avoiding the need to adjust the The DN value output of the measuring camera has many settable parameters, which makes the color correction work difficult.

(3) The invention helps to improve the synthetic accuracy of the true color of the aerospace remote sensing multi-spectral camera image.

Description of drawings

FIG. 1 is a schematic diagram of the optical path of the color correction test of the present invention.

detailed description

First, a brief introduction to the basic theory of colorimetry is given. The color of objects can be divided into two categories: self-luminous and non-luminous. The former is called the light source color, and the latter is called the object color. According to the principle of chromaticity, whether it is the color of the light source or the color of the object, its color mainly depends on the spectral power distribution of the light radiation directly entering the observer's eyes. The general formula for calculating the tristimulus value (XYZ) of a color is

In the formula: X, Y, Z—color tristimulus value;

K - normalization factor;

φ(λ)——the spectral power distribution of the light radiation directly entering the observer's eyes;

- Spectral tristimulus value of standard chromaticity observer;

Δλ——wavelength interval.

The color of the filter glass belongs to the transmitted object color. Therefore, its color depends on the relative spectral power distribution S(λ) of the lighting source and the spectral transmittance τ(λ) of the glass itself, that is, φ(λ)=S(λ)·τ(λ). So formula (1) can be rewritten as:

In the formula

Calculate the color tristimulus value according to formula (2). Then the chromaticity coordinates (CIE-xyz coordinates) are calculated by the formula (3).

In the formula: x, y, z are the chromaticity coordinates under the CIE-xyz coordinate system.

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

The invention introduces a multispectral camera color correction method. As shown in Figure 1, the device of the present invention comprises integrating sphere light source 1, transmissive 24-color standard color plate 3, light-shielding plate 4 with perforation, collimator 5, spectroradiometer 6, and its feature is because of: integrating sphere light source 1. The outgoing light beam passes through the color blocks on the transmissive 24-color standard color plate 3 and the light baffle plate 4 with openings, and reaches the focal plane of the collimator 5. After being collimated by the collimator, it enters the spectroradiometer 6, and then Get raw data.

The specific steps of the testing process of the color correction system of the present invention are as follows:

1) After the light emitted by the integrating sphere light source 1 is collimated by the collimator 5, parallel light is generated;

2) After setting up the multispectral camera to be tested at the light outlet of collimator 5, adjust the height, pitch angle and azimuth angle of the multispectral camera to be tested so that the color block A on the transmissive 24-color standard color plate 3 is in the position of the multispectral camera under test. Imaging on the spectrum camera; the color block A is the color block with the second highest transmittance among the gray scale color blocks on the transmissive 24-color standard color plate 3; adjust the output power of the integrating sphere light source 1, so that each of the measured multi-spectral cameras The spectral segments are all in the linear response region, and the output power of the integrating sphere light source 1 is fixed;

3) Remove the multi-spectral camera to be measured, set up the spectroradiometer 6 behind the light outlet of the collimator 5; adjust the height, elevation angle and azimuth angle of the spectroradiometer 6 so that the spectroradiometer 6 is coaxial with the collimator 5 ;

4) Adjust the positions of different color blocks on the transmissive 24-color standard swatch 3, and use the spectroradiometer 6 to collect the spectral radiance corresponding to each color block on the transmissive 24-color standard swatch 3 and the chromaticity under the CIE-xyz coordinate system coordinate;

5) Establish the relational equation of the color correction coefficient, the equivalent radiance of the multispectral camera, and the R, G, and B values after the color synthesis of the multispectral spectrum segment, and calculate and obtain the color correction coefficient; the relational equation is as follows:

Among them, L _B1 ~ L _B3 is the equivalent radiance of a certain color block area of the transmissive 24-color standard color palette 3 received by the multi-spectral camera under test; is the multi-spectral camera color correction coefficient matrix; R, G, and B are the final R, G, and B component values after the color synthesis of each spectral segment;

The calculation method of the correction coefficient of the present invention is: wherein the light source system output spectral radiance data obtained in the above step 2) can be combined with the relative spectral response curve of the camera to calculate L _B1 ~ L _B3 in the formula (4); The chromaticity coordinates (CIE-xyz) of different color block areas of different color blocks are converted to the RGB color space, and the R, G, and B values on the left side of the formula (4) can be obtained; each color block of the standard color plate corresponds to three equations, according to The practical application of the multispectral camera reasonably selects the test data of some color blocks (≥3 blocks), and then obtains a set of equations and solves them by the least square method to obtain the optimal solution of the 9 unknowns in the coefficient matrix to be sought.

The conversion method wherein the color coordinate values (CIE-xyz) of the different color patch regions measured by the spectroradiometer 6 to the RGB color space is: the color coordinate values (CIE-xyz) of the different color patch regions measured by the spectroradiometer 6 xyz coordinate system) can calculate the corresponding tristimulus value (XYZ tristimulus value) according to formula (2) and formula (3), and then convert to RGB color space, see formula (5) for the conversion formula.

Through the image data collected by the camera, the output DN value of the multi-spectral spectrum under the corresponding input conditions can be obtained. According to the gain of each spectral band, the integration series, and the setting of the integration time, the corresponding absolute calibration equation can be recalculated from the camera radiation calibration data, combined with the 3×3 color correction coefficient matrix obtained above, the camera can be calculated The final image after color compositing using this matrix.

The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims (1)

1. a kind of multispectral camera color correcting method, the system being related to includes integrating sphere light source (1), the colour standard color of transmission-type 24 Plate (3), the light barrier (4) with perforate, parallel light tube (5), spectral radiometer (6)；The light beam of integrating sphere light source (1) outgoing passes through Color lump on the colour standard colour table (3) of transmission-type 24 and the light barrier (4) with perforate, reach at parallel light tube (5) focal plane, through parallel Tested multispectral camera or spectral radiometer (6) are incided after light pipe (5) collimation, and then obtains initial data and image；It is described Perforate size on light barrier (4) with perforate and a color lump on the colour standard colour table (3) of transmission-type 24 are in the same size；It is special Sign is that step is as follows：

1) by the light of integrating sphere light source (1) outgoing after colour standard colour table (3) parallel light tube (5) of transmission-type 24 collimation, generation Directional light；

2) after tested multispectral camera being set up in into parallel light tube (5) light-emitting window, tested multispectral camera height, the angle of pitch are adjusted And azimuth, the color lump A on the colour standard colour table (3) of transmission-type 24 is imaged on tested multispectral camera；The color lump A is Penetrate on the colour standard colour table (3) of formula 24 the high color lump of transmitance second in gray scale color lump；Integrating sphere light source (1) power output is adjusted, Tested each spectral coverage of multispectral camera is set to be in linear response regions, and the power output of fixed integrating sphere light source (1)；

3) tested multispectral camera is removed, after spectral radiometer (6) is set up in into parallel light tube (5) light-emitting window；Adjust spectrum spoke Penetrating height, the angle of pitch and the azimuth of meter (6) makes spectral radiometer (6) coaxial with parallel light tube (5)；

4) transmission-type 24 colour standard colour table (3) different color blocks position is adjusted, uses the colour code of spectral radiometer (6) acquisition of transmission formula 24 Chromaticity coordinate on quasi- colour table (3) under spectral radiance and CIE-xyz coordinate systems corresponding to each color lump；

5) pass for R, G, B value established after the equivalent spoke brightness of color correction coefficient, multispectral camera, multispectral spectral coverage color formula It is equation, and calculates acquisition color correction coefficient；The relation equation is as follows：

<mrow> <mfenced open = "(" close = ")"> <mtable> <mtr> <mtd> <mi>R</mi> </mtd> </mtr> <mtr> <mtd> <mi>G</mi> </mtd> </mtr> <mtr> <mtd> <mi>B</mi> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <mfenced open = "(" close = ")"> <mtable> <mtr> <mtd> <msub> <mi>a</mi> <mn>1</mn> </msub> </mtd> <mtd> <msub> <mi>a</mi> <mn>2</mn> </msub> </mtd> <mtd> <msub> <mi>a</mi> <mn>3</mn> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>b</mi> <mn>1</mn> </msub> </mtd> <mtd> <msub> <mi>b</mi> <mn>2</mn> </msub> </mtd> <mtd> <msub> <mi>b</mi> <mn>3</mn> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>c</mi> <mn>1</mn> </msub> </mtd> <mtd> <msub> <mi>c</mi> <mn>2</mn> </msub> </mtd> <mtd> <msub> <mi>c</mi> <mn>3</mn> </msub> </mtd> </mtr> </mtable> </mfenced> <mo>&amp;CenterDot;</mo> <mfenced open = "(" close = ")"> <mtable> <mtr> <mtd> <msub> <mi>L</mi> <mrow> <mi>B</mi> <mn>1</mn> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>L</mi> <mrow> <mi>B</mi> <mn>2</mn> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>L</mi> <mrow> <mi>B</mi> <mn>3</mn> </mrow> </msub> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow>

Wherein, L_B1~L_B3Transmission-type 24 colour standard colour table (3) some color block areas received for tested multispectral camera Equivalent spoke brightness；For multispectral camera color correction coefficient matrix；R, G, B are respectively each spectral coverage color formula Final R, G, B component value afterwards；

L in the step 5)_B1~L_B3Calculating process be：

<mrow> <msub> <mi>L</mi> <mrow> <mi>B</mi> <mi>i</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msubsup> <mo>&amp;Integral;</mo> <mn>0</mn> <mi>&amp;infin;</mi> </msubsup> <mi>L</mi> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mo>)</mo> </mrow> <msub> <mi>R</mi> <mrow> <mi>B</mi> <mi>i</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mo>)</mo> </mrow> <mi>d</mi> <mi>&amp;lambda;</mi> </mrow> <mrow> <msubsup> <mo>&amp;Integral;</mo> <mn>0</mn> <mi>&amp;infin;</mi> </msubsup> <msub> <mi>R</mi> <mrow> <mi>B</mi> <mi>i</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mo>)</mo> </mrow> <mi>d</mi> <mi>&amp;lambda;</mi> </mrow> </mfrac> <mo>,</mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>3</mn> <mo>;</mo> </mrow>

Wherein, L (λ) is the spectral radiance data that spectral radiometer (6) demarcates parallel light tube (5) emergent light；R_Bi(λ) is tested The relative spectral response curve of multispectral camera Bi spectral coverages；

R, G, B calculating process are in the step 5)：

<mrow> <mfenced open = "(" close = ")"> <mtable> <mtr> <mtd> <mi>X</mi> </mtd> </mtr> <mtr> <mtd> <mi>Y</mi> </mtd> </mtr> <mtr> <mtd> <mi>Z</mi> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <mfenced open = "(" close = ")"> <mtable> <mtr> <mtd> <mn>2.7689</mn> </mtd> <mtd> <mn>1.7517</mn> </mtd> <mtd> <mn>1.1302</mn> </mtd> </mtr> <mtr> <mtd> <mn>1.0</mn> </mtd> <mtd> <mn>4.5907</mn> </mtd> <mtd> <mn>0.0601</mn> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mn>0.0565</mn> </mtd> <mtd> <mn>5.5943</mn> </mtd> </mtr> </mtable> </mfenced> <mfenced open = "(" close = ")"> <mtable> <mtr> <mtd> <mi>R</mi> </mtd> </mtr> <mtr> <mtd> <mi>G</mi> </mtd> </mtr> <mtr> <mtd> <mi>B</mi> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow> 1

WhereinX, y, z are the chromaticity coordinate under CIE-xyz coordinate systems.