How can I sharpen an image in OpenCV?

How can I sharpen an image using OpenCV?

There are many ways of smoothing or blurring but none that I could see of sharpening.

Solution 1:

One general procedure is laid out in the Wikipedia article on unsharp masking:

You use a Gaussian smoothing filter and subtract the smoothed version from the original image (in a weighted way so the values of a constant area remain constant).

To get a sharpened version of frame into image: (both cv::Mat)

cv::GaussianBlur(frame, image, cv::Size(0, 0), 3);
cv::addWeighted(frame, 1.5, image, -0.5, 0, image);

The parameters there are something you need to adjust for yourself.

There's also Laplacian sharpening, you should find something on that when you google.

Solution 2:

You can try a simple kernel and the filter2D function, e.g. in Python:

kernel = np.array([[-1,-1,-1], [-1,9,-1], [-1,-1,-1]])
im = cv2.filter2D(im, -1, kernel)

Wikipedia has a good overview of kernels with some more examples here - https://en.wikipedia.org/wiki/Kernel_(image_processing)

In image processing, a kernel, convolution matrix, or mask is a small matrix. It is used for blurring, sharpening, embossing, edge detection, and more. This is accomplished by doing a convolution between a kernel and an image.