make a grayscale heatmap from an image

Question

I'm trying to make a heatmap from a grayscaled image with cv2. The problem is, I get a strange looking image with this code:

import cv2
import numpy as np

img = cv2.imread('test.jpg', cv2.IMREAD_GRAYSCALE)

cv2.imshow('img', img)
cv2.waitKey(0)

hist = cv2.calcHist([img], [0], None, [256], [0, 256])
hist2 = np.uint8(hist)

heat = cv2.LUT(img, hist2)

cv2.imshow('img', heat)
cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

Not sure what do you mean by heatmap, but there are some colormaps in matplotlib which you can use to get similar results.

import matplotlib.pyplot as plt
import numpy as np
import cv2

image = cv2.imread('test.jpg', cv2.IMREAD_GRAYSCALE)
colormap = plt.get_cmap('inferno')
heatmap = (colormap(image) * 2**16).astype(np.uint16)[:,:,:3]
heatmap = cv2.cvtColor(heatmap, cv2.COLOR_RGB2BGR)

cv2.imshow('image', image)
cv2.imshow('heatmap', heatmap)
cv2.waitKey()

Also, you can use cv2.applyColorMap

image = cv2.imread('test.jpg', 0)
heatmap = cv2.applyColorMap(image, cv2.COLORMAP_HOT)