How to convert wand image object to open cv image (numpy array)

Question

I have imported wand using the following code

from wand.image import Image as WandImage
from wand.color import Color
with WandImage(filename=source_file, resolution=(RESOLUTION,RESOLUTION)) as img:
    img.background_color = Color('white')
    img.format        = 'tif'
    img.alpha_channel = False

How can i convert img object to open cv (cv2) image object in python?

emcconville · Accepted Answer · 2016-05-04 15:50:27Z

10

You would simply write to a byte-array buffer, and pass to cv2.imdecode.

from wand.image import Image as WandImage
from wand.color import Color
import numpy
import cv2

RESOLUTION=72
source_file='rose:'
img_buffer=None

with WandImage(filename=source_file, resolution=(RESOLUTION,RESOLUTION)) as img:
    img.background_color = Color('white')
    img.format        = 'tif'
    img.alpha_channel = False
    # Fill image buffer with numpy array from blob
    img_buffer=numpy.asarray(bytearray(img.make_blob()), dtype=numpy.uint8)

if img_buffer is not None:
    retval = cv2.imdecode(img_buffer, cv2.IMREAD_UNCHANGED)

answered May 4, 2016 at 15:50

emcconville

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2 Comments

dividebyzero Over a year ago

Just a comment on how this works, IIUC make_blob() returns the image encoded in another format, apparently BMP, which OpenCV can then understand and decode. It would be nice to find a way to directly create the array. Apparently numpy.asarray(img) should work here, but it doesn't really do the correct thing, it creates an array of "wand.color.Color" objects...

Vasilis Lemonidis Over a year ago

I faced a problem with alpha channel, while handling a pdf. It is better to put img.alpha_channel = 'remove' after having set the background color.

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