How to convert grayscale png with transparency to heatmap?

Question

The heatmap package isn't supported by Python 3, and cv2 doesn't support the following for PNG images with an alpha channel:

cv2.applyColorMap(img, cv2.COLORMAP_JET)

I want to convert a grayscale PNG image into a heatmap; in other words, colorize the darker pixels as blue and the brighter pixels as red.

Every pixel's transparency should remain unaffected.

Answer 1

Try using matplotlib.pyplot.get_cmap.

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

You can choose the color maps according to your desired output.