Question

I want to perform a Matrix calculation in OpenCV according to this formula:

newMat = 1 / ( 1 + exp( scalar * ( otherScalar - Matrix ) ) )

Is there an easy way to do this in OpenCV or do I have to calculate this in a for loop?
The main problem for me is the exp( Matrix ).

Regards

Answer 1

Maecky’s answer is perfectly fine – for 1-channel images.

The fun starts if your image has more than one channel. For some reasons,

float(scalar) - _3ChannelMat

applies the operation only on the first channel, while multiplication

float(scalar2) * _3channelMat

is done on all the channels of the image. Funny, isn’t it?

The solution is to use cv::Scalars:

newMat = cv::Scalar(0.4, 0.4, 0.4) * ( cv::Scalar(255, 255, 255) - _3channelMat);

I have filed a bug a while ago on this strange behaviour, but no answer yet.