Color calibration of an RGB camera mounted in front of a microscope with strong color distortion

Charrière, Renée; Hébert, Mathieu; Trémeau, Alain; Destouches, Nathalie

doi:10.1364/ao.52.005262

Cited by 26 publications

(34 citation statements)

References 23 publications

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“…A complete comparison between the four methods has been carried out, permitting an interesting discussion on the influence of different parameters on the calibration accuracy of each method, such as the diffusing properties of the color chart, and the polynomial order of the color transformation. Through our experiments, we conclude that the third method with 2 nd order degree polynomial fitting is the most accurate: by comparing the colors recorded by the device after transformation and those measured from our set of 50 specular testing samples, we obtained an average CIE-DeltaE94 color difference of 1.93 units, which is a good performance compared with previous studies 6,12,13 , based on diffusing materials where results between 2.2 and 3.0 units of CIE-DeltaE94 color difference were obtained. This method is already being used for color measurements of photochromic dyes created by laser insolation of clear plates 14 .…”

Section: Resultsmentioning

confidence: 50%

“…There were two different sets of colors used for this purpose: a diffuse color chart and a specular color chart. The diffuse chart was made of 48 pieces of Munsell Matte Color Sheets used in a previous study 6 , composed of 24 colors of similar appearance to the colors of the standard X-Rite ColorChecker® and 24 additional different colors to increase the color space sampling. The specular learning color chart was defined using the same procedure as the specular testing set, i.e., by placing colored filters on top of the Newport calibrated mirror, but with a different batch composed of 72 LEE Swatch Book -Numeric Edition® colored filters.…”

Section: Calibration Samplesmentioning

confidence: 99%

“…It has been demonstrated that both polynomial transformation and neural networks have similar performance even though polynomial transformations are easier to implement and require a smaller number of calibration samples to achieve good results 4 . For that reason, we use a polynomial transformation similar to the one used in a previous study 6 , by also performing, in addition to the 3rd degree polynomial fitting, 2nd and 4th degree fittings in order to study the effects of polynomial overfitting.…”

Section: Color Transformationmentioning

confidence: 99%

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Color calibration of an RGB digital camera for the microscopic observation of highly specular materials

2015

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International audienceColor calibration of imaging devices has been previously studied in a varied number of situations where the materials observed have diffuse or only slightly specular surfaces. Most of the calibration methods available in the literature consist in using standard diffuse color charts in order to determine the mathematical operations necessary to transform the colors measured by the imaging device into the reference colors obtained from the target chart. Unfortunately, there are many problems, such as sensor saturation, that arise when using these methods to calibrate devices intended for the observation of highly specular samples, especially in the 0°:0° illumination/observation geometry used in microscopic imaging systems. In this paper, we explore several color calibration methods adapted for the observation of highly specular materials, and propose one method in particular in which we use colored filters and a calibrated mirror in order to obtain a set of specular colored samples. By using 72 samples for learning, we tested the different methods on 50 other samples and obtained, with the best one, an average CIE-DeltaE94 color difference of 1.93 units, which is a fairly good performance for color measurements at the microscopic scale

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Section: Resultsmentioning

confidence: 50%

Section: Calibration Samplesmentioning

confidence: 99%

Section: Color Transformationmentioning

confidence: 99%

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Color calibration of an RGB digital camera for the microscopic observation of highly specular materials

2015

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“…A third order polynomial regression is used, according to a simplified method presented in Ref. [33], in order to find a transformation P , containing the polynomial regression coefficients, that maps the input R, G, B values to the M optical thicknesses of primaries. At the third order, the matrix P representing the calibration of the predictive model is a  20 M matrix: …”

Section: From Rgb Color To Spectral Reflectancementioning

confidence: 99%

Prediction of the spectral reflectance of laser-generated color prints by combination of an optical model and learning methods

et al. 2015

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. Prediction of the spectral reflectance of laser-generated color prints by combination of an optical model and learning methods. Journal of the Optical Society of America. A Optics, Image Science, and Vision, Optical Society of America, 2015, 32 (9) Recent color printing technologies based on the principle of revealing colors on pre-functionalized achromatic supports by laser irradiation offer advanced functionalities, especially for security applications. However, for such technologies the color prediction is challenging, compared to classic ink-transfer printing systems. The spectral properties of the coloring materials modified by the lasers are not precisely known and may strongly vary, depending on the laser settings, in a nonlinear manner. We show in this study, through the example of the Color Laser Marking technology based on laser-bleaching of a mixture of pigments, that the combination of an adapted optical reflectance model and learning methods to get the model's parameters enables predicting the spectral reflectance of any printable color with rather good accuracy. Even though the pigment mixture is formulated from three colored pigments, an analysis of the dimensionality of the spectral space generated by CLM printing, thanks to a Principal Component Analysis decomposition, shows that at least four spectral primaries are needed for accurate spectral reflectance predictions. A polynomial interpolation is then used to relate RGB laser intensities with virtual coordinates of new basis vectors. By studying the influence of the number of calibration patches on the prediction accuracy, we can conclude that a reasonable number of 130 patches are enough to achieve good accuracy in this application.

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“…Furthermore, a variety of color calibration methods exist to further improve the color fidelity of bright-field microscopy systems2829303132333435.…”

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confidence: 99%

Color calibration and fusion of lens-free and mobile-phone microscopy images for high-resolution and accurate color reproduction

Zhang

et al. 2016

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Lens-free holographic microscopy can achieve wide-field imaging in a cost-effective and field-portable setup, making it a promising technique for point-of-care and telepathology applications. However, due to relatively narrow-band sources used in holographic microscopy, conventional colorization methods that use images reconstructed at discrete wavelengths, corresponding to e.g., red (R), green (G) and blue (B) channels, are subject to color artifacts. Furthermore, these existing RGB colorization methods do not match the chromatic perception of human vision. Here we present a high-color-fidelity and high-resolution imaging method, termed “digital color fusion microscopy” (DCFM), which fuses a holographic image acquired at a single wavelength with a color-calibrated image taken by a low-magnification lens-based microscope using a wavelet transform-based colorization method. We demonstrate accurate color reproduction of DCFM by imaging stained tissue sections. In particular we show that a lens-free holographic microscope in combination with a cost-effective mobile-phone-based microscope can generate color images of specimens, performing very close to a high numerical-aperture (NA) benchtop microscope that is corrected for color distortions and chromatic aberrations, also matching the chromatic response of human vision. This method can be useful for wide-field imaging needs in telepathology applications and in resource-limited settings, where whole-slide scanning microscopy systems are not available.

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Color calibration of an RGB camera mounted in front of a microscope with strong color distortion

Cited by 26 publications

References 23 publications

Color calibration of an RGB digital camera for the microscopic observation of highly specular materials

Color calibration of an RGB digital camera for the microscopic observation of highly specular materials

Prediction of the spectral reflectance of laser-generated color prints by combination of an optical model and learning methods

Color calibration and fusion of lens-free and mobile-phone microscopy images for high-resolution and accurate color reproduction

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