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Problem 17 – Measurement of color sensitivity

Problem 17 – Measurement of color sensitivity. Presenter: Kalina Stoimenova Team: Bulgaria - Sofia. Main problem. 17. Measurement of color sensitivity

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Problem 17 – Measurement of color sensitivity

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  1. Problem 17 – Measurement of color sensitivity Presenter: KalinaStoimenova Team: Bulgaria - Sofia

  2. Main problem 17. Measurement of color sensitivity Some people (called color blind persons) have difficulties comparing the colors of two objects. But most people perceive the color difference at the first glimpse. The difficulties arise when the colors are hardly distinguishable, e.g. if colors of two leaves from the same tree need to be compared. How is it generally possible to quantitatively estimate the ability of a person to distinguish the color shades? Is a single numerical parameter sufficient, or a more complicated evaluation system is required?

  3. Table of contents

  4. What is colorimetry? Part of optics investigating the properties of the colors on a quantitative level

  5. Perception of color • Factors influencing the perception of color: • Source of light (spectral distribution of its EM energy) • The observer (personal sensitivity)

  6. Standard color vision Summing curves for the different color receptors.

  7. Two dimensional color space Each color is represented by two coordinates in this space (x,y) CIE 1931

  8. Experimental set up • We used: • spectral photometer SPEKOL-11 • pieces of paper of different colors • two pieces of tree leaves

  9. Coefficient of reflection • Each color has different coefficient of reflection, depending on the wavelength of the incident light Ir – reflected light intensity I0 – initial intensity (incident)

  10. Coefficient of reflection • We measured the coefficients of reflection for these standard wavelengths

  11. Experimental results

  12. Experimental results

  13. Normalized color coordinates • For each color we calculate the normalized (to 1) coordinates, x, y and z,using the following relations: • We need only two of the them, because they sum up to 1.

  14. Positions in the 2D color space • The calculated normalized coordinates are the following: Blue: x = 0.22; y = 0.26 Yellow: x = 0.45; y = 0.49

  15. Equally contrast space • In order to be able to compare two colors we introduce the equally contrast space coordinates: • Here X0, Y0 and Z0– the coordinates of the white sample, used for calibration.

  16. Color difference • If we have measured the equally contrast coordinates of two colors, the quantity: is called color difference. If the human eye is able to distinguish the two colors.

  17. Results Using that in our case: X0=98,041, Y0 = 100,00 and Z0 = 118,103. • We calculated: • The color difference between the blue and yellow is: 124.

  18. Experiment with leaves • We have used the following two pieces of tree leaves

  19. Experiment with leaves

  20. Experiments with leaves

  21. Experiment with leaves • We calculated the following values for the equal contrast coordinates: • And the calculated color difference is: 8,6. • We should be able to distinguish their colors!

  22. Conclusions

  23. Thank you for your attention!

  24. References • 1.Handbook of laboratory practicum of optics – Sofia University “St. Kliment Ohridski” • 2. http://en.wikipedia.org/wiki/CIE_1931_color_space

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