Automatic colorimetric calibration of human wounds

Abstract

BackgroundRecently, digital photography in medicine is considered an acceptable tool in many clinical domains, e.g. wound care. Although ever higher resolutions are available, reproducibility is still poor and visual comparison of images remains difficult. This is even more the case for measurements performed on such images (colour, area, etc.). This problem is often neglected and images are freely compared and exchanged without further thought.MethodsThe first experiment checked whether camera settings or lighting conditions could negatively affect the quality of colorimetric calibration. Digital images plus a calibration chart were exposed to a variety of conditions. Precision and accuracy of colours after calibration were quantitatively assessed with a probability distribution for perceptual colour differences (dE_ab). The second experiment was designed to assess the impact of the automatic calibration procedure (i.e. chart detection) on real-world measurements. 40 Different images of real wounds were acquired and a region of interest was selected in each image. 3 Rotated versions of each image were automatically calibrated and colour differences were calculated.Results1st Experiment: Colour differences between the measurements and real spectrophotometric measurements reveal median dE_ab values respectively 6.40 for the proper patches of calibrated normal images and 17.75 for uncalibrated images demonstrating an important improvement in accuracy after calibration. The reproducibility, visualized by the probability distribution of the dE_ab errors between 2 measurements of the patches of the images has a median of 3.43 dE* for all calibrated images, 23.26 dE_ab for all uncalibrated images. If we restrict ourselves to the proper patches of normal calibrated images the median is only 2.58 dE_ab! Wilcoxon sum-rank testing (p < 0.05) between uncalibrated normal images and calibrated normal images with proper squares were equal to 0 demonstrating a highly significant improvement of reproducibility. In the second experiment, the reproducibility of the chart detection during automatic calibration is presented using a probability distribution of dE_ab errors between 2 measurements of the same ROI.ConclusionThe investigators proposed an automatic colour calibration algorithm that ensures reproducible colour content of digital images. Evidence was provided that images taken with commercially available digital cameras can be calibrated independently of any camera settings and illumination features.

Histomorphometry of the Ligaments Using a Generic-Purpose Image Processing Software, a New Strategy for Semi-Automatized Measurements

“…The computerized morphometry is useful in several medical fields for objective color analysis and characterization of biological tissues. It is used in very different fields, for example, for the quantitative measurement of liver fibrosis [3], quantification of erythema and pigmentation [4,5], and calibration of human wounds [6]. Our group has been conducting histomorphometric studies on ligaments [7] using a nonspecific commercial image analysis.…”

Concurrent validation and reliability of digital image analysis of granulation tissue color for clinical pressure ulcers

“…Our results indicated that the most two common methods of color calibration were not sufficient to standardize the color properties in clinical settings because they produced approximately 20% of the error, as indicated by the variance of the color marker. In particular, it is known that the error in quantifying the red color would be greater than that for other colors evaluated with image analysis 30 . Because of this measurable error, it is possible that the traditional EI, for which validity has been confirmed in laboratory settings, 15,16 cannot accurately reproduce the clinical red color.…”

“…In particular, it is known that the er-ror in quantifying the red color would be greater than that for other colors evaluated with image analysis. 30 Because of this measurable error, it is possible that the traditional EI, for which validity has been confirmed in laboratory settings, 15,16 cannot accurately reproduce the clinical red color. An adequate standardization of photographic brightness may be difficult to achieve solely by ensuring a standardized photographic environment or usual color calibration.…”

Color standardization in whole slide imaging using a color calibration slide

“…Instead of adopting this approach we adopted the approach proposed in[23] wherein color correction is implemented in the linear RGB color space rather than in the CIE XYZ color space. This could be advantageous with respect to computational cost considering the huge file size of the whole slide image.…”