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Dichromaticity index (DI) is a measure for quantification of dichromatism. It is defined as the difference in hue angle (Δhab) between the color of the sample at the dilution, where the chroma (related to color saturation) is maximal and the color of four times more diluted (or thinner) and four times more concentrated (or thicker) sample. The two hue angle differences are called dichromaticity index towards lighter (DIL) and dichromaticity index towards darker (DID) respectively. The dichromaticity index DIL and DID for pumpkin seed oil, which is one of the most dichromatic substances are -9 and -44, respectively. This means, that pumpkin seed oil changes its color from green-yellow to orange-red (for 44 degrees in Lab color space) when the thickness of the observed layer is increased from cca 0.5 mm to 2 mm; and it changes slightly towards green (for 9 degrees) if its thickness is reduced for 4-fold.

Follow the link to download free Dichromaticity Index Calculator software, and a test pumpkin seed oil spectrum, or any other spectrum in .txt file format. (Please note that after installation the application may take several seconds to start. Some computers may need to be restarted after the installation.)

Alternatively, you can also download the algorithm in Excel file. You will need to enable macros in MS Excel.