MATLAB: Imfilter at single point

Question

Lets suppose you have an image and a filter of the same size. I want to know how to find the filtered value of the midpoint of the image without filtering the rest of the image.

I am currently using imfilter and then using the midpoint of the output. This is obviously computationally expensive, so if there is a way to circumvent this, please let me know!

Thanks

Answer 1

Just multiply and add. Something like (untested)

productImage = double(grayImage) .* filterImage;
centerValue = sum(productImage(:));