问题
Basically I want to create of a halo effect for the image that fades to transparent.
I have images of wounds (and their masks), with no background. I want to add a red gradient behind it, that way if I paste it on something it looks like the area surrounded the wound is irritated.
image and mask ...
Originally, I was making a radial (circle) gradient and pasted my transparent image on it, but this does not look good for my non circular images.
image with circle gradient
same image as above,but pasted on white easier to see gradient
...
Now, i think the best idea would be to make the gradient in a shape the goes around the edge of the image to a certain distance and fades. something like this ( i did this poorly with paint ... but basically for it to go out a certain distance, from the edge of the object, and fade out)
paint version of what i would like to do ...
My code for the the circle gradient is posted below, this creates a transparent circle gradient. Once i have this i paste my transparent image on it. I do not know how to change this code so that it creates the gradient the edge of the image.
import numpy as np,
from PIL import Image
W,H=900,900
im = Image.new(mode='RGB', size=(W,H), color=(153,0,0))
Y = np.linspace(-1, 1, H)[None, :]*255
X = np.linspace(-1, 1, W)[:, None]*255
alpha = np.sqrt(X**2 + Y**2) # equation of a circle
alpha = 255 - np.clip(0,255,alpha)
Please help
来源：https://stackoverflow.com/questions/62456912/how-to-create-a-transparent-gradient-along-the-edge-of-an-image-mask-image-with