Methods to Calibrate a Digital Colour Camera as a Multispectral Imaging Sensor in Low Light Conditions
Round 1
Reviewer 1 Report
The manuscript lacks precision evaluation and comparison, which cannot verify the progressiveness of the method.
The structure of the entire article is somewhat chaotic, and I hope the author can rearrange the order of the article. Here are three suggestions:
1. The introduction section of the article does not provide a detailed explanation of the experimental background, how the experiment was conducted in previous studies, what are the shortcomings of these methods, and what are the advantages of the proposed method in this manuscript.
2. The research data and experiments were not uniformly introduced in the manuscript, but were distributed in the methods and results section. For example, Figures 3, 4, 6, and 7 should not be placed in the methods section, as they are more like experimental results. And equations (10) - (15) should be appeared in the method section;
3. Try to place the figures and tables next to the text description.
Some other suggestions
Page 3, figure 2，suggest to give a comparison figure between customer-grade camera with scientific purposes camera, not only the Bayer filter.
Page 9, line 207, “ε is the physical size of a pixel …”, I cannot find ε in equation.
Figure 8，where is the blue area
Page 13, line 283, page 14, figure 15, it seems that the fitting result is not very accurate, for that residual is almost 0.05°
Author Response
Thank you for the review.
Modifications to the article based on your suggestions and those of the other reviewers are highlighted in red.
Overall, the proposed method isn't meant to be an improvement over already existing ones, but rather be more accessible. As such, the text was changed in various places to make this distinction clearer.
Below are specific answers to the suggestions made:
1. The introduction was expanded and more previous works were cited.
2. The referenced figures were presented in the methodology section to illustrate the methods and justify the need for some of the calibration steps. Figures 4 and 6 have been moved to the "Results" section, but the authors believe Figures 3 and 7 should stay in the "Methodology" section since they are not direct results of the calibration method.
Similarly, equations 10-15 serve a specific purpose in the "Example application" section, and it would significatively break the flow of the article to place them in the methodology. However, this part of the article was moved to its own section to better emphasize its place in the context of this work.
3. Final placement of the Figures is left to the editor, but an effort was made to place them closer to their reference in the text.
Figure 2: A new figure presenting the alternative to a filter matrix was added.
Equation 7: The equation was fixed.
Figure 8: The authors are unsure how to address this comment, as the Figure only presents a yellow and a blue area, both of which are referenced in the caption. The blue area goes from 1.5r to 2r.
Figure 15: 0.05 degrees is not a significant residual when looking at the position of stars in a 50 degrees wide field of view. The text was modified to specify that this accuracy is sufficient.
Reviewer 2 Report
Dear Authors,
The paper presents a detailed and thorough calibration procedure to make non-scientific multispectral sensors in e.g. DLSS cameras suitable for scientific studies.
The publication is recommended for acceptance after the authors have made the modifications raised in the following comments and questions:
Section 2.1:
- In the averaging process described, which physical parameters of the pixels were investigated (e.g., resulting signal intensity)? Please provide more details in the text.
Section 2.8:
- I suggest further support for the method described for star photography with relevant references.
- Formulas 2 and 7 are incorrectly displayed in the pdf, notations have slipped. Please correct this.
Section 3.1.4:
- typo in title: correct "tree colour band" to "three colour bands"
Section 3.2:
- It is not clear what relevance is the analysis of the images from the statospheric balloon to the topic of the article? Is the camera used here calibrated according to the above method? Is this section trying to validate the method? Please emphasize more its role in the article.
Figure 3:
- It would facilitate the reader's understanding if more explanation of what is shown in subsets a-f is provided. For subset f, there is no information on the y-axis.
Figures 18 and 19:
- I suggest using coordinate scales on the edges of maps to make the location data on them more informative.
- In Figure 19, it is not possible to identify which detail of Figure 18 is shown.
The overall quality of language is good, I found some minor typo and slipping of formula that needs to be revised.
Author Response
Thank you for the review.
Modifications to the article based on your suggestions and those of the other reviewers are highlighted in red.
Below is our response to your comments and questions.
Section 2.1 :
The fact that we are interested by the resulting signal intensity has been clarified.
Section 2.8 :
- We are unsure what specific part of the process would need further referencing, as this section already cites 9 sources for various parts of the process.
- The formulas have been fixed.
Section 3.1.4 (now 3.4) :
- Typo fixed.
Section 3.2 (now 4) :
- A paragraph was added to better explain the role of this part of the work in the context of the article.
Figure 3 (now 4) :
- The figure itself was not modified as it is reproduced as is from the cited reference.
Figures 18 and 19 (now 19 and 20) :
- A new figure (Fig. 21) was added to illustrate the extent of the two figures on compared with the map of the city of Timmins.
Reviewer 3 Report
I am not sure that I am qualified for this review but The article has addresses all of the areas that I am aware of such as flat frames, distortion, thermal effects, and zero points to name a few. In addition, it could a great resource for many as a low cost option for night time imagery.
A couple of suggestions
Section 2.3 is awkward, reorder as
-- A camera must allow direct control of exposure time and digital gain (ISO) for the images produced to be used for scientific purposes.
Line 168 Eq. 2
This equation doesn't match the text and seems corrupted or confusing.
Figure 9 needs to have the X and dot in the legend or mentioned in the caption of the figure.
Line 380 - might expand here - is 3% good, good enough, how does it compare with a more expensive camera.
Author Response
Thank you for the review.
Modifications to the article based on your suggestions and those of the other reviewers are highlighted in red.
Your suggestions have all been addressed. For the last one, I do not know how the method compares with other cameras, as we don't have access to one in order to compare. The overall text has been modified to not present the method in comparison to scientific cameras but how it's stand on it's own.
Round 2
Reviewer 1 Report
This paper describes a workflow for constructing a radiation correction using a commercial camera instead of a professional camera. The ideas in this paper have some merit, but the process and results in this paper are not rigorous. The author has made some improvements compared to the previous version, but the article still has major problems. Therefore, I recommond rejecting it for publication.
Most of the methods in this paper are not innovative. Professional cameras can also follow the ideas in this paper. But the key to the calibration is to get the accurate parameters, which is somewhat weakly demonstrated in the paper. The authors make more assumptions and conditions in the atmospheric aspect, which I think may lead to lower accuracy of the obtained calibration parameters.
I hope the authors can add some accuracy assessment in the experimental section. For example, the illuminance comparison between the method from this paper and from actual measurement.
Author Response
Thank you for the review.
We feel that the work does have some merit since the method being applicable to consumer electronics and for low light levels specifically has not been thoroughly explored.
Your argument that a proper comparison was needed, and we agree. We added comparison between the calibrated system and a spectrometer and find results within a few percent points of each other.
Changes to the article from the previous version are highlighted in red.
