Anthony Anthony - 7 months ago 28
Python Question

How to remote 4th channel from PNG images

I am loading images from a URL in OpenCV. Some images are PNG and have four channels. I am looking for a way to remove the 4th channel, if it exists.

This is how I load the image:

def read_image_from_url(self, imgurl):
req = urllib.urlopen(imgurl)
arr = np.asarray(bytearray(req.read()), dtype=np.uint8)
return cv2.imdecode(arr,-1) # 'load it as it is'


I don't want to change the
cv2.imdecode(arr,-1)
but instead I want to check whether the loaded image has a fourth channel, and if so, remove it.

Something like this but I don't know how to actually remove the 4th channel

def read_image_from_url(self, imgurl):
req = urllib.urlopen(imgurl)
arr = np.asarray(bytearray(req.read()), dtype=np.uint8)
image = cv2.imdecode(arr,-1) # 'load it as it is'
s = image.shape
#check if third tuple of s is 4
#if it is 4 then remove the 4th channel and return the image.

Answer

You need to check for the number of channels from img.shape and then proceed accordingly:

# In case of grayScale images the len(img.shape) == 2
if len(img.shape) > 2 and img.shape[2] == 4:
    #convert the image from RGBA2RGB
    img = cv2.cvtColor(img, cv2.COLOR_BGRA2BGR)
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