When scaling an image, you can call cv2.resize() with a specific size, and the scaling factors (fx and fy) will be calculated based on the provided size, as shown in the following code:
resized_image = cv2.resize(image, (width * 2, height * 2), interpolation=cv2.INTER_LINEAR)
On the other hand, you can provide both the fx and fy values. For example, if you want to shrink the image by a factor of 2, you can use the following code:
dst_image = cv2.resize(image, None, fx=0.5, fy=0.5, interpolation=cv2.INTER_AREA)
If you want to enlarge the image, the best approach is to use the cv2.INTER_CUBIC interpolation method (a time-consuming interpolation method) or cv2.INTER_LINEAR. If you want to shrink the image, the general approach is to use cv2.INTER_LINEAR.
The five interpolation methods provided with OpenCV are cv2.INTER_NEAREST (nearest neighbor interpolation), cv2.INTER_LINEAR (bilinear interpolation), cv2.INTER_AREA (resampling using pixel area relation), cv2.INTER_CUBIC (bicubic interpolation), and cv2.INTER_LANCZOS4 (sinusoidal interpolation).