Sharpening an image using emgu
I know this answer is very late but I think this question worth an answer 

The algorithm you used goes as follows: 


Blur the original image using the Gaussian filter with given Mask Size &amp; Sigma
Subtract the blurred image from the original (result is called Mask) to eliminate background and get the edges regions
Add a weighted portion from the mask to the original image by multiplying the Mask (the edges only) by K to enhance edges regions  


K: User input (If K = 1 Unsharp, If K > 1 Highboost) 

Mask(x,y) = Orig(x,y) – Blurred(x,y)

Result(x,y) = Orig(x,y) + K × Mask(x,y)

Here is the code: 

public static Image&lt;Gray, byte&gt; Sharpen(Image&lt;Gray, byte&gt; image, int w, int h, double sigma1, double sigma2, int k)
    {
        w = (w % 2 == 0) ? w - 1 : w;
        h = (h % 2 == 0) ? h - 1 : h;
        //apply gaussian smoothing using w, h and sigma 
        var gaussianSmooth = image.SmoothGaussian(w, h, sigma1, sigma2);
        //obtain the mask by subtracting the gaussian smoothed image from the original one 
        var mask = image - gaussianSmooth;
        //add a weighted value k to the obtained mask 
        mask *= k;
        //sum with the original image 
        image += mask;
        return image;
    }


I think your problem is that you didn't subtract the smoothed image from the original image, anyway I hope this help