CODEWITHSUNDEEP
pythonpython-3.xpython-imaging-library
Watashi
Watashi

Reputation: 13

Python pillow: problem with threshold transparency

I'm trying to convert png to bmp 256 8 bits indexed colors, but I can't figure out how to set a threshold to make partial transparent pixels become transparent, original and result:

Image

Here's my code:

from PIL import Image
import os

def convert_to_indexed_bmp(input_image_path, output_bmp_path):
    img = Image.open(input_image_path)

    indexed_background_color = (0, 255, 0)

    img_with_indexed_background = Image.new("RGBA", img.size, indexed_background_color)
    img_with_indexed_background.paste(img, (0, 0), img)

    img_indexed = img_with_indexed_background.convert("RGB").convert("P", palette=Image.ADAPTIVE, colors=256)

    img_indexed.save(output_bmp_path)

input_folder = "splash.png"
output_folder = "splash.bmp"


convert_to_indexed_bmp(input_folder, output_folder)

How to cut off this green edges?

Upvotes: 1

Views: 148

Answers (1)

Mark Setchell
Mark Setchell

Reputation: 207798

I can't tell from your question what you actually want to do, but hopefully you can get what you want by reading the following.

#!/usr/bin/env python3

from PIL import Image

# Load input image
im = Image.open('z.png')

# Create lime green  output image of same size
res = Image.new('RGBA', im.size, 'lime')

# Let's analyse the alpha channel
alpha = im.getchannel('A')
alpha.save('DEBUG-alpha.png')

# Derive new alpha channel, thresholding at 127
newAlpha = alpha.point(lambda p: 255 if p>127 else 0)
 
# Now paste image with new alpha onto background and save
res.paste(im, (0,0), newAlpha)
res.save('result.png')

This is DEBUG-alpha.png:

enter image description here

which shows your alpha values vary between 0 and 255. You seem to want to do something with the partially transparent pixels - but I can't tell if you want to make all of them fully transparent, or all of them fully opaque or maybe just some of them. Nor do I know why you paste onto a green background if you don't want green in your output image. Anyway, look at the line that says:

newAlpha = alpha.point(lambda p: 255 if p>127 else 0)

and change it according to what you need.

enter image description here

Maybe you want this:

newAlpha = alpha.point(lambda p: 0 if p>0 and p<140 else 255)

enter image description here

Upvotes: 0

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