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Problem about the source codes of otsu-threshold

asked 2013-09-19 01:36:58 -0500

stereomatching gravatar image

updated 2013-09-19 03:15:28 -0500

berak gravatar image

The codes from the files thresh.cpp, the function name is getThreshVal_Otsu_8u

if( std::min(q1,q2) < FLT_EPSILON || 
            std::max(q1,q2) > 1. - FLT_EPSILON )
            continue;

As far as I know,

q1 + q2 = 1--(1)
q1 = 1 - q2--(2)
q2 = 1 - q1--(3)

That means if

q1 < FLT_EPSILON

then 1 - q1 will satisfy

1 - q1 > 1 - FLT_EPSILON

In other words, if std::min(q1,q2) < FLT_EPSILON, then std::max(q1,q2) > 1. - FLT_EPSILON should satisfy too.So why do the codes need to do double check? Why don't just use

if( std::min(q1,q2) < FLT_EPSILON)
                continue;
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answered 2013-09-19 04:03:55 -0500

Moster gravatar image

Probably this has something to do with float precision. It might happen that one of the conditions returns false/true although it shouldnt with real numbers.

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Comments

This look reasonable, do you know other possibility?

stereomatching gravatar imagestereomatching ( 2013-09-19 04:46:03 -0500 )edit

No, actually I dont. This is most likely the reason

Moster gravatar imageMoster ( 2013-09-22 14:40:34 -0500 )edit
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Asked: 2013-09-19 01:36:58 -0500

Seen: 161 times

Last updated: Sep 19 '13