JP5066137B2 - Gas concentration measuring apparatus and gas concentration measuring method - Google Patents

Description

  The present invention relates to a gas concentration measuring apparatus and a gas concentration measuring method for measuring a gas concentration by a colorimetric method.

At present, air pollution due to NOx, SPM, and photochemical oxidants occurs, and the impact on the environment has become a problem. Ozone gas (O ₃ ), the main component of photochemical oxidants, is generated when pollutants such as NOx and hydrocarbons emitted from factories, offices, and automobiles are exposed to sunlight and cause a photochemical reaction. Cause. Also, in various devices equipped with corona discharge means, such as electrostatic copying machines, laser printers, LED facsimiles, etc., ozone gas and NOx gas are generated during the operation of the corona discharge means. Since such ozone gas has a strong oxidizing ability, if its concentration in the air exceeds a certain level (0.1 ppm) due to its own toxicity, it stimulates the respiratory system and is harmful if inhaled for a long time even in trace amounts. It is said that.

Also, nitrogen dioxide (NO ₂ ), which is one of NOx, is easily absorbed from the lungs and shows a strong oxidative action in the cells to damage the cells, causing mucosal irritation, bronchitis, pulmonary edema, etc. . These are also air pollutants that cause photochemical smog and acid rain.

  In addition, when paying attention to the home environment and the workplace environment, sick house syndrome due to VOC (volatile organic compounds) including formaldehyde is a problem.

  For this reason, it is necessary to investigate and monitor the concentration of gases harmful to the human body and environmental problems. Among the aforementioned harmful gases, various ozone concentration measuring devices that are inexpensive, small and light, and can be used at an individual or household level have been developed for ozone gas (see, for example, Patent Documents 1 to 4). As such a simple ozone concentration measuring device, ozone concentration detection paper shown in Non-Patent Document 1 is sold. This ozone concentration detection paper is provided with a detection paper that fades when exposed to ozone gas and a color sample corresponding to the concentration of ozone gas. This ozone concentration detection paper is produced by impregnating a cellulose filter paper with a detection solution prepared by adding a dye, a moisturizing agent, an acid, water, or the like that fades when it reacts with ozone gas.

Similarly, a NO ₂ sensor (see Patent Literature 5) and a formaldehyde sensor (see Non-Patent Literature 2) have been developed as sensors that utilize the change in color of the sensing element.

  Any of the above-described sensing elements reacts with the target gas to change the reflection spectrum in the visible region. Conventionally, the concentration of the target gas has been calculated by measuring the reflectance change of one wavelength where the spectral change is the largest by visual observation by the human eye. However, the concentration measurement by visual observation can measure only a rough concentration. Further, if a spectrophotometer or a dedicated device for measuring the change in reflectance at a specific wavelength is used, accurate measurement is possible, but it is expensive and cannot be purchased and used by general users.

  In such a situation, an attempt is made to take an image of the detection element with a digital camera or the like and calculate the gas concentration from the color information.

JP 2004-144729 A International Publication No. 2006/016623 JP 09-274032 A Japanese Patent Laid-Open No. 2000-081426 JP 2001-116738 A

"Ozone visible sheet", NTT Advanced Technology Corporation, [Search May 25, 2009], Internet <URL: http://shop.ntt-at.co.jp/ozone/000_product0/> Maruko Yoko, 5 others, "Measurement of formaldehyde in indoor and furniture using β-ditoken detector", Environmental Chemistry, 2008, Vol. 18, No. 4, p.501-509

  However, since an image captured with a digital camera has a non-constant shooting environment (type of light source and illuminance), there is a problem that calculating the ozone concentration with absolute values of color information such as RGB values has a large error. For example, the ozone concentration detection paper described in Non-Patent Document 1 is adjusted to the same color as when the ozone concentration detection paper was exposed to ozone at 0 ppb × hour, 120 ppb × hour, 240 ppb × hour, 320 ppb × hour. The color chart is enclosed. Even when the ozone concentration detection paper and the color chart are photographed so as to fit within the same image, even if the RGB value of the ozone concentration detection paper shows exactly the middle of the color chart of 0 ppb × hour and 120 ppb × hour, the ozone concentration detection When the ozone accumulation exposure amount of paper is calculated as 60 ppb × hour, there is a problem that an error becomes large. Depending on the shooting conditions, an error of about 40 ppb × hour at the maximum occurred.

  This is because the RGB values of the electronic image data obtained by photographing the sensing element and the reflection absorbance (-log (reflectance)) of the sensing element measured with a spectrophotometer or the like are not linear. A sensing element whose spectrum in the visible region changes by reaction with the target gas can calculate the accumulated gas exposure (gas concentration x time) from the change in the reflected absorbance at a specific wavelength, but it can be obtained from electronic image data. RGB information is not linearly related to reflected absorbance. In addition, since the relationship between the RGB value and the reflected absorbance varies greatly each time depending on the illumination environment and the photographing apparatus, a conversion formula for converting the RGB value into the reflected absorbance cannot be created.

  The present invention has been made in view of the above, and an object thereof is to calculate the target gas concentration more accurately using electronic image data obtained by photographing a colorimetric gas detection element.

  The gas concentration measuring apparatus according to the first aspect of the present invention includes a detection region whose color changes according to the amount of gas exposure, and a reference region whose reflection absorbance having a color corresponding to at least three known exposure amounts is known. A gas exposure amount detection means, an input means for receiving input of image data obtained by photographing the gas exposure amount detection means, an extraction means for extracting color information of a position corresponding to the detection region and the reference region from the image data, and a reference A relative value obtained by comparing the color information of the detection area with the color information of the reference area and the correction means for correcting the color information so that the relationship between the color information of each area and the reflection absorbance corresponding to each of the reference areas is linear. And calculating means for calculating the amount of gas exposure by applying to a predetermined conversion formula.

  The gas concentration measurement apparatus according to the second aspect of the present invention includes a detection region whose color changes according to the exposure amount of the gas, a first reference region having a color corresponding to at least two known exposure amounts, and at least Gas exposure amount detection means having a second reference region with known reflection absorbances, input means for receiving input of image data obtained by photographing the gas exposure amount detection means, detection regions and first and second from the image data The color information so that the relationship between the color information of the second reference area and the reflection absorbance corresponding to each of the second reference areas is linear. And a calculating means for calculating the gas exposure amount by applying a relative value obtained by comparing the color information of the detection area with the color information of the first reference area to a predetermined conversion formula. Features.

  In the gas concentration measuring apparatus, the correction means corrects the color information by gamma correction or tone curve correction.

  A gas concentration measurement method according to a third aspect of the present invention includes a detection region whose color changes according to the amount of gas exposure, and a reference region whose reflection absorbance having a color corresponding to at least three known exposure amounts is known. Receiving an input of image data obtained by photographing a gas exposure amount detection means having a step of extracting color information of a position corresponding to the detection region and the reference region from the image data, color information of each reference region and the reference region By applying a relative value obtained by comparing the color information of the detection area with the color information of the reference area to the predetermined conversion formula by correcting the color information so that the relationship with the corresponding reflected absorbance is linear. And calculating the exposure amount.

  A gas concentration measurement method according to a fourth aspect of the present invention includes a detection region whose color changes according to the amount of gas exposure, a first reference region colored with at least two known exposure amounts, and at least A step of receiving an input of image data obtained by photographing the gas exposure amount detection means having a second reference region having three known reflection absorbances, and a position corresponding to the detection region and the first and second reference regions from the image data. Extracting the color information; correcting the color information so that the relationship between the color information of each of the second reference areas and the reflection absorbance corresponding to each of the second reference areas is linear; and And calculating a gas exposure amount by applying a relative value obtained by comparing the color information with the color information of the first reference region to a predetermined conversion formula.

  In the gas concentration measuring method, the correcting step corrects the color information by gamma correction or tone curve correction.

  According to the present invention, the target gas concentration can be calculated more accurately using electronic image data obtained by photographing the colorimetric gas detection element.

It is a block diagram which shows the structure of the gas concentration measurement system in 1st Embodiment. It is a flowchart which shows the flow of the process in which the said gas concentration measurement system calculates ozone accumulation exposure amount. It is a figure explaining correction | amendment of the RGB value of a reference area. It is a figure explaining another correction | amendment of the RGB value of a reference area. It is a figure explaining the example of the tone curve used for the correction | amendment of FIG. It is a top view which shows the structure of the detection sheet | seat used with the gas concentration measurement system in 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, an example of measuring the ozone concentration will be described, but the present invention can be similarly applied to other gases.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of a gas concentration measurement system in the present embodiment. The gas concentration measurement system shown in the figure includes a detection sheet 10, an imaging device 20, and a gas concentration measurement device 30. A detection sheet 11 and a color chart 12 are arranged on the detection sheet 10. The gas concentration measurement system transmits electronic image data of the detection sheet 10 photographed by the photographing device 20 to the gas concentration measurement device 30, and the gas concentration measurement device 30 compares the color change of the detection paper 11 with the color chart 12. To calculate the gas concentration.

  The detection paper 11 is a paper in which indigo carmine is held in a porous body. Since there is an absorption peak at a wavelength of 620 nm, the detection paper 11 shows a blue color when not used, and changes to white when exposed to ozone gas. The color chart 12 requires at least three colors and desirably has a large number of colors. The color chart 12 shown in FIG. 1 includes regions 12A to 12E corresponding to five colors corresponding to different gas exposure amounts of the detection paper 11, and the reflection spectrum of each region 12A to 12E is completely the same as the reflection spectrum of the detection paper 11. Identical. It is desirable that the detection paper 11 and the color chart 12 have a reflection spectrum as close as possible. This is because, even if the human eye or digital camera recognizes the same color (same RGB value) under a certain lighting environment, the absorption peak position of the reflection spectrum is different. This is because the eyes and digital camera do not recognize the same color. If the reflection spectra are the same, the detection paper 11 and the color chart 12 are identified as the same color under any light source having any power spectrum. The detection paper 11 may include an acid and a humectant.

  As the photographing device 20, a device that captures an image electronically such as a digital camera or a digital video camera can be used.

  The gas concentration measurement device 30 includes an input unit 31, an extraction unit 32, a correction unit 33, and a calculation unit 34. The gas concentration measurement device 30 may be configured by a computer including an arithmetic processing device, a storage device, a memory, and the like, and the processing of each unit may be executed by a program. This program is stored in a storage device included in the gas concentration measuring device 30, and can be recorded on a recording medium such as a magnetic disk, an optical disk, or a semiconductor memory, or provided through a network. Hereinafter, each part will be described.

  The input unit 31 receives input of electronic image data of the detection sheet 10 captured by the imaging device 20.

  In the input electronic image data, the extraction unit 32 specifies a detection area where the detection paper 11 is captured and a reference area where each of the areas 12A to 12E of the color chart 12 is captured, and acquires RGB values for each area. To do.

  The correction unit 33 performs gamma correction or tone curve correction on the obtained RGB value of each region. Correction is performed so that the relationship between the RGB values of the regions 12A to 12E acquired from the electronic image data and the reflected absorbance is linear. The reflection absorbance at a specific wavelength in each of the regions 12A to 12E is measured in advance and stored in the memory as reference data in association with the RGB values of the regions 12A to 12E. Details of the correction will be described later.

  The calculation unit 34 calculates the ozone accumulation exposure amount by applying a relative value obtained by comparing the corrected RGB value of the reference region and the RGB value of the detection region to a predetermined conversion formula.

  Next, the flow of processing in which the gas concentration measurement system calculates the ozone accumulation exposure amount will be described with reference to the drawings. FIG. 2 is a flowchart showing a flow of processing in which the gas concentration measurement system calculates the ozone accumulation exposure amount.

  First, the detection sheet 10 is imaged by the imaging device 20, and the gas concentration measurement device 30 inputs electronic image data (step S11). The imaging device 20 images the detection sheet 10 so that the detection paper 11 and the color chart 12 are captured.

  Subsequently, the extraction unit 32 specifies the positions of the areas 12A to 12E of the detection paper 11 and the color chart 12 on the electronic image data, and acquires RGB values for each of the six areas in total (step S12). Since there is an RGB value for each pixel, the RGB value of each region is obtained by calculating the average value of the RGB values for each pixel in that region. Alternatively, the mode may be calculated as the RGB value by creating a histogram for each region. By using the mode value, it is possible to eliminate the influence on the calculated RGB value even when a shadow or a foreign object appears in a part of the area or a character is printed.

  Subsequently, the correction unit 33 performs gamma correction or tone curve correction so that the RGB values of the respective regions 12A to 12E of the color chart 12 have a linear relationship with the reflected absorbance (step S13). The reflection absorbances of the regions 12A to 12E of the color chart 12 are measured in advance and are known values. Since the detection paper 11 has an absorption peak at a wavelength of 620 nm, the reflection absorbance of each region 12A to 12E of the color chart 12 at 620 nm is measured. Assume that the reflection absorbances of the regions 12A to 12E are 3.0 for the region 12A, 2.8 for the region 12B, 2.6 for the region 12C, 2.4 for the region 12D, and 2.2 for the region 12E. In addition, since the R value changes most greatly among the RGB values, the R value is compared with the reflected absorbance of each of the regions 12A to 12E of the color chart 12 at 620 nm. When the value of R is plotted on the vertical axis, the value of reflected absorbance is plotted on the horizontal axis, and the values of R in the respective regions 12A to 12E before correction are illustrated, the relationship between the value of R and the reflected absorbance as shown by the white circles in FIG. Is not linear. Therefore, gamma correction or tone curve correction is performed so that the relationship between the R value and the reflected absorbance is linear. In the example shown in FIG. 3, gamma correction is performed with a gamma value of 1 or less so as to lower the R value of the intermediate gradation. On the other hand, when it is desired to correct the halftone R value to increase, the gamma correction is performed with a gamma value of 1 or more. For example, the gamma correction may be performed by gradually shifting the gamma value, and the result obtained with the best gamma value for the correlation coefficient between the regression line of the RGB value and the reflected absorbance may be employed.

  FIG. 4 shows another correction example. When the contrast of the photographing apparatus 20 is set to be high or low, the relationship between the R value of each of the regions 12A to 12E before correction and the reflected absorbance is S-shaped or reverse S as shown by the white circle in FIG. It becomes a letter. Such a case cannot be dealt with by gamma correction, so it is dealt with by tone curve correction. For example, a point corresponding to the RGB value of the region 12A and a point corresponding to the RGB value of the region 12E are connected by a straight line, and the corrected RGB value is obtained from the intersection of the straight line and each reflection absorbance. If tone curve correction is used, the position of the inflection point of the tone curve can be freely changed, so that correction can be made more accurately.

  FIG. 5 shows an example of a tone curve. In FIG. 5, two inflection points are set, but the inflection points are set with respect to five points in the regions 12A to 12E with the RGB values before correction as input values and the corrected RGB values as output values. When tone curve correction is performed after setting, the relationship between RGB values and reflected absorbance is linear. In addition, the RGB values before correction are plotted on the horizontal axis as input values and the RGB values after correction are plotted on the vertical axis as output values for the five points in the regions 12A to 12E, and the nonlinear least square method is plotted for the five points. The fitting curve may be calculated by using the curve as a tone curve, and tone curve correction may be performed.

  After correcting the RGB values, the calculation unit 34 substitutes a relative value obtained by comparing the RGB values of the corrected regions 12A to 12E and the RGB values of the detection paper 11 into a predetermined conversion formula to store the accumulated ozone exposure (concentration × Time). (Step S14). The detection paper 11 has a performance in which the reflected absorbance changes in proportion to the ozone accumulation exposure amount, and the reflection absorbance at 620 nm changes from 2.84 to 2.20 by the ozone accumulation exposure 320 ppb × hour. Expressed as (1), a change in reflection absorbance of 0.01 corresponds to 5 ppb.

Ozone accumulation exposure amount = 320 × {(2.84−reflection absorbance) / (2.84-2.20)} (1)
The reflection absorbance of the formula (1) can be obtained by associating the RGB values of the detection paper 11 with the straight lines in FIGS. In the method of the present invention, by correcting the RGB values of the electronic image data, the reflected absorbance can be estimated with an accuracy of ± 0.02 or less, and the ozone accumulation exposure can be measured with an error of 5 to 10 ppb × hour or less. it can.

  In addition, it is clear that the detection paper 11 changes the reflection absorbance in proportion to the ozone accumulation exposure amount, and the electronic image data is corrected so that the relationship between the RGB value and the reflection absorbance is linear. The ozone accumulation exposure amount can be obtained using the following equation (2).

Ozone accumulation exposure amount = 320 × {(RGB value of darkest color chart−RGB value of detection paper) / (RGB value of darkest color chart−RGB value of lightest color chart) } ... (2)
In this way, by correcting the electronic image data so that the relationship between the RGB values of the color chart 12 and the reflected absorbance is linear, even when the illumination environment and the photographing apparatus 20 are variously changed, they are affected. The gas concentration can be measured with higher accuracy.

  As described above, according to the present embodiment, it becomes widespread by performing gamma correction or tone curve correction so that the relationship between the RGB value of each region 12A to 12E of the color chart 12 and the reflected absorbance is linear. Even when a digital camera or the like is used as the photographing apparatus 20, the RGB value of the detection paper 11 can be accurately converted into the reflected absorbance by removing or reducing the influence of the illumination conditions and the photographing apparatus. As a result, the gas concentration can be accurately measured by the detection paper 11 in which the relationship between the gas exposure amount and the reflection absorbance is clarified. Previously, a spectrophotometer and a dedicated device for measuring the reflectance at a specific wavelength were required, but in addition to a colorimetric detector, a highly accurate gas concentration measurement using a combination of a popular digital camera and personal computer Is possible and the introduction cost is reduced.

[Second Embodiment]
Next, a second embodiment will be described. Since the configuration of the gas concentration measurement system is almost the same as that of the first embodiment, only the parts different from the first embodiment will be described.

  In the first embodiment, the color chart 12 having the regions 12A to 12E corresponding to five colors corresponding to different gas exposure amounts of the detection paper 11 and having the same reflection spectrum is used. In addition, it is expensive to prepare a number of color charts 12 having the same reflection spectrum as that of the detection paper 11. Ordinary inks are made with a combination of about 3 to 5 inks that show an absorption peak at a specific wavelength, except for black and gray, where the reflection absorbance is constant at any wavelength. It is difficult to get close, and even if the detection paper and the color chart are the same color under the fluorescent light, they will look different under sunlight. Some ink companies can make a custom color chart with a reflection spectrum close to that of the detection paper, but the cost becomes very expensive, and increasing the number of colors in the color chart becomes difficult in terms of cost.

  Therefore, in the second embodiment, as shown in FIG. 6, the first color chart 52 of two colors having a reflection spectrum that is the same as or close to the reflection spectrum of the detection paper 51, and gamma correction or tone curve correction are performed. For this purpose, a detection sheet 50 including at least a second color chart 53 of at least three colors is used. The first color chart 52 includes a region 52A having the same color as the unused detection paper 51 and a region 52B having the same color as the detection paper 51 that has been sufficiently exposed to the target gas and no longer changes in color (saturated). Become. The second color chart 53 includes six color regions 53A to 53F from white to black, and the reflection absorbances of the regions 53A to 53F are known.

  In the second embodiment, after performing gamma correction or tone curve correction using the second color chart 53, the reflection absorbance is calculated from the RGB values of the detection paper 51 and the first color chart 52, and the gas concentration is calculated. Is calculated. Hereinafter, correction of electronic image data and calculation of gas concentration in the second embodiment will be described.

  First, electronic image data in which the detection sheet 50 is copied is input, and a total of nine areas, that is, the detection paper 51, the areas 52A and 52B of the first color chart 52, and the areas 53A to 53F of the second color chart 53 are input. Get RGB values for the region.

  Subsequently, gamma correction or tone curve correction of the electronic image data is performed using the areas 53A to 53F of the second color chart 53, and then the areas 52A and 52B of the detection paper 51 and the first color chart 52 are corrected. The reflected absorbance of the detection paper 51 is obtained using the RGB values, and is substituted into Equation (1) to obtain the ozone gas accumulated exposure amount. Alternatively, the RGB values of the detection paper 51 and the areas 52A and 52B are substituted into the equation (2).

  As described above, the second color chart 53 for performing gamma correction or tone curve correction is provided separately from the first color chart 52 for obtaining the reflection absorbance of the detection paper 51, so that the detection paper 51 and the reflection spectrum are provided. Therefore, the number of colors of the first color chart 52 that is the same or close to each other can be suppressed, and the production cost of expensive custom ink can be reduced.

[Modification]
In the first and second embodiments, a digital camera or a camera attached to a mobile phone is preferably used as the photographing device 20. In addition, by using a digital camera with an interval shooting function or a web camera, it is possible to obtain electronic image data of a detection sheet unattended every fixed time. The captured electronic image data may be input to the gas concentration measurement device 30 via a network. A commercially available personal computer is preferably used as the gas concentration measuring device 30.

  Further, by photographing the detection sheet a plurality of times at a predetermined interval, the average ozone concentration during that time can be calculated using the difference from the previous ozone gas accumulation exposure amount and the elapsed time. When a digital camera or the like is used, information such as the shooting date and time is present in the electronic image data, so that it is possible to easily know the elapsed time from the previous time by referring to the information.

  In addition, since the detection papers 11 and 51 using the chemical reaction change the gas detection sensitivity and the reflected absorbance due to the influence of the temperature and humidity conditions, the correction equations for the gas detection sensitivity and the reflected absorbance according to the temperature and humidity conditions are tested in advance. The measurement accuracy of the gas concentration can be improved by measuring the temperature and humidity simultaneously with photographing.

  When the target gas is formaldehyde, a β-diketone held in a porous body is used as a colorimetric gas detection element. At least one of acetylacetone or 1-phenyl-1,3-butanedione is used as the β-diketone.

  Further, when the target gas is nitrogen dioxide, a diazo coupling reagent held in a porous body is used as a colorimetric gas detection element.

  In the case of paper other than ozone detection paper, it is desirable to use the wavelength having the largest variation width due to exposure to the target gas for the reflected absorbance, and the RGB value to be the color value having the largest variation width in the color change.

DESCRIPTION OF SYMBOLS 10 ... Detection sheet 11 ... Detection paper 12 ... Color chart 20 ... Imaging device 30 ... Gas concentration measuring device 31 ... Input part 32 ... Extraction part 33 ... Correction | amendment part 34 ... Calculation part 50 ... Detection sheet 51 ... Detection paper 52 ... 1st Color chart 53 ... Second color chart

Claims (6)

A gas exposure amount detection means having a detection region whose color changes according to the exposure amount of the gas, and a reference region having a known reflection absorbance with a color corresponding to at least three known exposure amounts;
Input means for receiving input of image data obtained by photographing the gas exposure amount detection means;
Extraction means for extracting color information of positions corresponding to the detection area and the reference area from the image data;
Correction means for correcting the color information so that the relationship between the color information of each reference region and the reflection absorbance corresponding to each of the reference regions is linear;
A calculation means for calculating a gas exposure amount by applying a relative value obtained by comparing the color information of the detection area with the color information of the reference area to a predetermined conversion formula;
A gas concentration measuring device comprising: A detection region whose color changes in response to the amount of gas exposure, a first reference region colored with at least two known exposure amounts, and a second reference region with at least three known reflection absorbances. Gas exposure detection means having,
Input means for receiving input of image data obtained by photographing the gas exposure amount detection means;
Extraction means for extracting color information at positions corresponding to the detection area and the first and second reference areas from the image data;
Correction means for correcting the color information so that the relationship between the color information of each of the second reference areas and the reflection absorbance corresponding to each of the second reference areas is linear;
Calculating means for calculating a gas exposure amount by applying a relative value obtained by comparing the color information of the detection area with the color information of the first reference area to a predetermined conversion formula;
A gas concentration measuring device comprising:   3. The gas concentration measuring apparatus according to claim 1, wherein the correction unit corrects the color information by gamma correction or tone curve correction. Image data obtained by photographing a gas exposure amount detection means having a detection region whose color changes in accordance with the gas exposure amount and a reference region having a known reflection absorbance with a color corresponding to at least three known exposure amounts. Accepting input, and
Extracting color information of positions corresponding to the detection area and the reference area from the image data;
Correcting the color information so that the relationship between the color information of each of the reference regions and the reflection absorbance corresponding to each of the reference regions is linear;
Calculating a gas exposure amount by applying a relative value obtained by comparing the color information of the detection region with the color information of the reference region to a predetermined conversion formula;
A gas concentration measuring method comprising: A detection region whose color changes in response to the amount of gas exposure, a first reference region colored with at least two known exposure amounts, and a second reference region with at least three known reflection absorbances. Receiving an input of image data obtained by photographing the gas exposure amount detection means having;
Extracting color information of positions corresponding to the detection area and the first and second reference areas from the image data;
Correcting the color information so that the relationship between the color information of each of the second reference areas and the reflection absorbance corresponding to each of the second reference areas is linear;
Calculating a gas exposure amount by applying a relative value obtained by comparing the color information of the detection region with the color information of the first reference region to a predetermined conversion formula;
A gas concentration measuring method comprising:   6. The gas concentration measuring method according to claim 4, wherein the correcting step corrects the color information by gamma correction or tone curve correction.

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