Quantifying color changes in chemical test pads induced by different concentrations of analytes under different lighting conditions
Color quantification of chemical test pads and titration of analytes can be performed under different lighting conditions. In one embodiment, the lighting condition is estimated under which a digital image is captured and utilized to select a set of reference colors from which the quantified color is compared to determine the titration. In another embodiment, a plurality of comparisons are made with different lighting conditions with the result having the highest confidence level being selected to determine the titration.
1. A method for quantifying color change of at least one test medium on a diagnostic instrument, the method comprising:
obtaining a digital image of at least a portion of the diagnostic instrument that has been exposed to a biological sample, the diagnostic instrument comprising at least one color reference including a plurality of reference samples of different colors and at least one test medium containing a reagent that changes color in response to a concentration of a particular analyte in the biological sample;
identifying at least one reference sample of the plurality of reference samples for the at least one test medium in the diagnostic instrument;
determining a dominant camera-captured color of the at least one reference sample and a dominant camera-captured color of the at least one test medium;
estimating lighting conditions under which the digital image is obtained;
correcting the dominant camera-captured color of the at least one test medium, in response to a color correction factor derived at least in part from the dominant camera-captured color of the at least one reference sample, to determine a corrected test medium color; and
determining a test result including an analyte concentration of the biological sample based on the corrected test medium color.
2. The method of claim 1 , wherein the diagnostic instrument comprises a plurality of test media arranged in a plurality of test specific sequences.
3. The method of claim 1 , wherein the diagnostic instrument further comprises an identification label including or associated with identification information about the diagnostic instrument, and wherein the digital image of the diagnostic instrument includes at least a portion of the identification label.
4. The method of claim 3 , wherein the identification label is at least one of the following: a bar code; a QR code, a near-field communication tag, or any combination thereof.
5. The method of claim 3 , wherein the identification information includes at least one of the following:
a manufacture date of the diagnostic instrument;
an expiration date of the diagnostic instrument;
the analytes tested for by the instrument;
identifying information about a test subject; or
patient condition information.
6. The method of claim 3 , further comprising validating the diagnostic instrument by analyzing the portion of the digital image including the identification label to determine the identification information.
7. The method of claim 6 , further comprising determining whether the diagnostic instrument is in condition for use based on the identification information.
8. The method of claim 3 , wherein the identifying step further comprises:
scanning the digital image to determine a position of the identification label on the digital image;
determining geometric corrections for the digital image based at least in part on the position of the identification label, the geometric corrections comprising one or more angles of rotation of the diagnostic instrument about one or more of an x-axis, a y-axis, a z-axis, or any combination thereof; and
calculating the position of the at least one reference sample and the at least one test medium on the digital image based at least partially on the position of the identification label and the geometric corrections.
9. The method of claim 1 , wherein the identifying step further comprises:
identifying a region of the digital image containing the at least one reference sample; and
removing background artifacts from the identified region by applying a variance operator to remove portions of the identified region having low variance and maintaining portions of the identified region having high variance.
10. The method of claim 9 , wherein the identifying step further comprises:
identifying a region of the digital image including the at least one reference sample and a region of the digital image including the at least one test medium;
identifying edge artifacts on a boundary of the identified regions; and
removing identified edge artifacts from the digital image.
11. The method of claim 1 , wherein the determining the dominant camera-captured color further comprises:
defining spatial guard bands around or just within a boundary of the at least one reference sample and the at least one test medium to form enclosed areas; and
reducing color noise within the enclosed areas of the at least one reference sample and the at least one test medium by averaging the color within the enclosed areas.
12. The method of claim 11 , further comprising applying a median filter to at least one enclosed area to determine the dominant color therein.
13. The method of claim 1 , wherein the color correcting step further comprises:
identifying a reference sample that is white in the digital image;
determining the correction factor based at least partially on an average color of the white reference sample in the digital image; and
color correcting the color of the at least one test medium by applying the correction factor using a white balancing algorithm.
14. The method of claim 1 , wherein the color correcting step further comprises:
determining luminescence of the at least one reference sample from the estimated lighting conditions;
comparing the luminescence of the at least one reference sample to a predetermined expected luminescence to determine a luminescence correction factor;
comparing the dominant camera-captured color of the at least one reference sample with an expected sample color to determine a color correction factor; and
correcting the camera-captured color of the at least one test medium based at least partially on the luminescence correction factor and the color correction factor.
15. The method of claim 1 , further comprising rejecting the digital image if the corrected test medium color exceeds a predetermined value.
16. The method of claim 1 , wherein the camera-captured reference sample and the camera-captured test medium color each comprise a plurality of color components defining at least one color space, and wherein the at least one color space is at least one of the following:
red-green-blue (RGB) color space; cyan-magenta-yellow-key (CMYK) color space;
International Commission on Illumination (CIE) XYZ color space;
International Color Consortium (ICC) device independent color space (L*a*b color space);
pantone color space; or
Munsell color space.
17. A system for performing diagnostic tests of a biological sample, the system comprising:
a diagnostic instrument comprising a color reference comprising a plurality of reference samples of different colors and a plurality of test media containing a plurality of reagents, wherein the plurality of reagents change color in the presence of various levels of a plurality of different analytes in a biological sample; and
a portable electronic device comprising a digital camera sensor for capturing a digital image of at least a portion of the diagnostic instrument and a processor, wherein the processor is configured to:
identify at least one of the reference samples and at least one of the test media in the digital image of the diagnostic instrument;
determine a dominant camera-captured color of a reference sample and a dominant camera-captured color of the at least one test media;
estimate lighting conditions under which the digital image is captured;
correct the dominant camera-captured color of the at least one test media, in response to a color correction factor derived at least in part from the dominant camera-captured color of the reference sample, to determine a corrected test media color; and
determine a test result including an analyte concentration of the biological sample based on the corrected test media color.