Python unsharp mask

Question

I want to use unsharp mask on a 16 Bit Image.

The Image has 640 x 480 Pixels and is saved in a NumPy array.

I have done the following:

• blurred the image with a Gaussian filter (three different methods)
• then, created a mask by subtracting the blur Image form the original
• finally, added the mask multiplied by WightFaktor to the original Image

But it doesn´t really work.

Here is the Python code:

Gaussian1 = ndimage.filters.gaussian_filter(Image,sigma=10.0)
Gaussian2 = filters.gaussian_filter(Image,sigma=10.0)
Gaussian3 = cv2.GaussianBlur(Image,(9,9),sigmaX=10.0)

Mask1 = Image - Gaussian1
UnsharpImage = Image + (WightFaktor*Mask1)

Answer 1

To get an unsharp image using OpenCV you need to use the addWeighted function as follows:

import cv2

image = cv2.imread("example.jpg")
gaussian_3 = cv2.GaussianBlur(image, (0, 0), 2.0)
unsharp_image = cv2.addWeighted(image, 2.0, gaussian_3, -1.0, 0)
cv2.imwrite("example_unsharp.jpg", unsharp_image)

Giving the following kind of result:

addWeighted() is used here as follows:

dst = cv2.addWeighted(src1, alpha, src2, beta, gamma)

Giving you the following transformation:

dst = src1*alpha + src2*beta + gamma

The strength of the effect can be altered by adjusting the alpha and beta weightings, for example: 1.5 and -0.5.