Is there a way to use Pillows “Image.convert()” on an existing variable?

Question

Hello,

maybe this question looks stupid, but I try to use Pillows Image.convert() to convert an image to grayscale. This image I have store

Answer 1

Whilst you could perfectly well convert your Numpy array to a PIL Image and then convert that to greyscale and then convert back to a Numpy array like this:

PILImage = Image.fromarray(Numpyimg)
PILgrey  = PILImage.convert('L')
Numpygrey= np.array(PILgrey)

You might as well just do the ITU-R 601-2 luma transform yourself, i.e.

L = 0.299 * Red + 0.587 * Green + 0.114 * Blue

So, you would get:

Numpygrey = np.dot(Numpyimg[...,:3], [0.299, 0.587, 0.114]).astype(np.uint8)