Convert image to BGRA color space without using opencv-CodePudding

Is it possible to convert an RGBA image to BGRA without using the following code, i.e. without using opencv?

image = self.cv2.cvtColor(image, self.cv2.COLOR_RGBA2BGRA)

CodePudding user response：

You can convert an image from BGRA to RGBA with this line of code:

image[..., :3] = image[..., 2::-1]

Of course, it modifies the existing array rather than creating a new one (which is good if you don't plan on using the old one again as it's more efficient). Another way is image = image[..., [2,1,0,3]], but since it uses fancy indexing, rather than modifying the old array, it creates a copy of the old array which takes up more memory.

Using the same line of code again converts the image back from RGBA to BGRA.

CodePudding user response：

Like this with "fancy indexing":

# Make a dummy, random 4-channel image
RGBA = np.random.randint(0,256,(2,3,4), np.uint8)

In [3]: RGBA
Out[3]: 
 array([[[102, 204,  36, 128],
         [178, 151, 166,  45],
         [199,  49, 104,  98]],

        [[ 79,  33, 223,  62],
         [ 26,  34, 233, 254],
         [ 62,  20,  57, 149]]], dtype=uint8)

# Convert RGBA to BGRA
BGRA = RGBA[..., [2,1,0,3]]

In [5]: BGRA
Out[5]: 
array([[[ 36, 204, 102, 128],
        [166, 151, 178,  45],
        [104,  49, 199,  98]],

       [[223,  33,  79,  62],
        [233,  34,  26, 254],
        [ 57,  20,  62, 149]]], dtype=uint8)

I think OpenCV likes its data contiguous, so if you get issues, use:

BGRA = RGBA[..., [2,1,0,3]].copy()