Figure 4. Color calibration results of a mobile-phone based microscope and a benchtop microscope.

(a) A transmission-mode color checker (#1) with 22 patches was custom-fabricated. (b) The measured colors of each patch of (a) obtained using lens-free hyperspectral imaging, which were used as the ground truth in the training of the color calibration. (c) A color checker (#2) with 24 additional patches was fabricated using the same procedure as in (a). These additional color patches were used to improve the accuracy of the color calibration. (d) The ground truth colors of (c) measured by lens-free hyperspectral imaging. (e) Colors captured by our mobile-phone microscope using 2.7× magnification before the color calibration is applied. The small triangle in the upper left corner of each patch is the ground truth color from (b,d), while the rest of the patch is the color captured by the mobile-phone based microscope. (f) The colors in (e) plotted in the CIE 1931 chromaticity diagram, where “+” represents ground truth color and “” represents the captured color. Without calibration, the color aberration is quite large. (g,h) the colors after the color calibration is performed, using the same convention as (e,f). The colors after this calibration match to the ground truth very well. The quantitative color errors are also listed in Table 1. (i–l) The same process as in (e–h) using a benchtop microscope with a 10× 0.3 NA objective lens.