Blend Two Images Using An Alpha Value

Overview:

  • An alpha channel in an image introduces transparency to the Image.

 

  • Alpha blending combines two images by applying an alpha value to the images.

 

  • Pillow –Python Image Processing Library provides blend() method as part of the Image class implementation.

 

  • When Image1 and Image2 are blended using alpha value 0, Image1 is returned as and vice versa when the alpha value is 1.

 

  • When the alpha value varies from 0 to 1 and beyond, interpolation is used to determine the color value given by the formula

 

out=((int) in1[x] + alpha * ((int) in2[x] - (int) in1[x]));

Example:

from PIL import Image

# Function to change the image size
def changeImageSize(maxWidth, 
                    maxHeight, 
                    image):
    
    widthRatio  = maxWidth/image.size[0]
    heightRatio = maxHeight/image.size[1]

    newWidth    = int(widthRatio*image.size[0])
    newHeight   = int(heightRatio*image.size[1])

    newImage    = image.resize((newWidth, newHeight))
    return newImage
    
# Take two images for blending them together   
image1 = Image.open("./sky1.png")
image2 = Image.open("./spaceship1.png")

# Make the images of uniform size
image3 = changeImageSize(800, 500, image1)
image4 = changeImageSize(800, 500, image2)

# Make sure images got an alpha channel
image5 = image3.convert("RGBA")
image6 = image4.convert("RGBA")

# Display the images
image5.show()
image6.show()

# alpha-blend the images with varying values of alpha
alphaBlended1 = Image.blend(image5, image6, alpha=.2)
alphaBlended2 = Image.blend(image5, image6, alpha=.4)

# Display the alpha-blended images
alphaBlended1.show()
alphaBlended2.show()

Output:

Image1 used in blending:

Image1 for blending using an alpha value - Pillow example

Image2 used in blending:

Image2 for blending using an alpha value - Pillow example

Alpha blended Image - alpha=0.2:

Alpha blended image 1, alpha = 0.2

Alpha blended Image - alpha=0.4:

Alpha blended image 2 - alpha = 0.4


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