Colour filters arc commonly used in monochrome photography for altering the relative lightness of different coloured parts of the original scene when recorded in the image. However, the choice of filter is not straightforward where it is necessary to enhance contrast between closely similar colours. The concept of exposure density can be used to quantify the effect on the image of different filters, combined with the effect of the spectral properties of all the system’s parameters such as the light source, response of the sensor and transmittance of the camera lens.
This method can be applied to any other imaging system and is not restricted to visible radiation. Calculations of predicted exposure density difference, or system exposure response difference (SERD) for a digital image, provide the basis for the selection of the optimum filters and other system parameters for maximizing image contrast in the recording of closely similar colours.
Palmer, J.R. and Jacobson, R.E., 1994. Determination and enhancement of image contrast using the exposure density concept. The Journal of Photographic Science, 42(1), pp.35-39.
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Category: Photonics & Optoelectronics