Food and other biological products are valued by their appearance. Appearance is a major factor in the judgment of quality and human eye has historically done this. The colour indicates parameters like ripeness, defects, etc. The quality decisions vary among the graders and often inconsistent. The adaptation of human eye to small changes in colour and the effect of the background on the perceived colour and colour intensity are the main sources of error. Hence, it is hard to provide precise guideline for visual inspection of fruits based on colour. In biological products, the light varies widely as a function of wavelength. These spectral variations provide a unique key to machine vision and image analysis. Machine vision technology offers the solution for all these problems. Of the many available colour models, HSI model provides a highly effective colour evaluation particularly for analyzing biological products. Using an RGB colour camera, it is also possible to obtain the colour information. However since the RGB colour model represents the image in three separate coordinates RED, GREEN and BLUE, it is not efficient for colour perception and image processing than compared to HSI model, where 'H' alone gives the colour perception.
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