MATLAB: I couldn’t understand convex area

convexareaImage Processing Toolbox

 i know ''area'' command calculates the number of pixels in the region.
 As far as i see,  The value of ''ConvexArea'' is bigger than ''area'' 
 In regionprops,  The term ''ConvexArea'' what is it exactly? 
what does it calculate? For what purpose can we use this property?

Best Answer

Hi Selim,
the 'convexArea' property corresponds the area of the convex hull of the region. The convex hull of a region is the smallest region that satisfy two conditions: (1) it is convex (2) it contains the original region.
The convex area is by definition greater than or equal to the area of the region. It can be used to compute a shape factor known either as "convexity" or "solidity", defined as the ratio of area over convex area. It can be obtained by using the 'solidity' parameter in regionprops function.
The solidity can be used to discriminate or classify regions using shape criteria.
regards,
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