CODEWITHSUNDEEP
pythonimage
Ritambhara Chauhan
Ritambhara Chauhan

Reputation: 99

Edit image pixel by pixel - Python

I have two images, one overlay and one background. I want to create a new image, by editing overlay image and manipulating it to show only the pixels which have blue colour in the background image. I dont want to add the background, it is only for selecting the pixels. Rest part should be transparent. Any hints or ideas please? PS: I edited result image with paint so its not perfect.

Image 1 is background image.

Image 2 is overlay image.

Image 3 is the check I want to perform. (to find out which pixels have blue in background and making remaining pixels transparent)

Image 4 is the result image after editing.

backgroundoverlaycheckresult

Upvotes: 1

Views: 1780

Answers (1)

Mark Setchell
Mark Setchell

Reputation: 207465

I renamed your images according to my way of thinking, so I took this as image.png:

enter image description here

and this as mask.png:

enter image description here

Then I did what I think you want as follows. I wrote it quite verbosely so you can see all the steps along the way:

#!/usr/local/bin/python3
from PIL import Image
import numpy as np

# Open input images
image = Image.open("image.png")
mask  = Image.open("mask.png")

# Get dimensions
h,w=image.size

# Resize mask to match image, taking care not to introduce new colours (Image.NEAREST)
mask = mask.resize((h,w), Image.NEAREST)    
mask.save('mask_resized.png')

# Convert both images to numpy equivalents
npimage = np.array(image)
npmask  = np.array(mask)

# Make image transparent where mask is not blue
# Blue pixels in mask seem to show up as RGB(163 204 255)
npimage[:,:,3] = np.where((npmask[:,:,0]<170) & (npmask[:,:,1]<210) & (npmask[:,:,2]>250),255,0).astype(np.uint8)

# Identify grey pixels in image, i.e. R=G=B, and make transparent also
RequalsG=np.where(npimage[:,:,0]==npimage[:,:,1],1,0)
RequalsB=np.where(npimage[:,:,0]==npimage[:,:,2],1,0)
grey=(RequalsG*RequalsB).astype(np.uint8)
npimage[:,:,3] *= 1-grey

# Convert numpy image to PIL image and save
PILrgba=Image.fromarray(npimage)
PILrgba.save("result.png")

And this is the result:

enter image description here

Notes:

a) Your image already has an (unused) alpha channel present.

b) Any lines starting:

npimage[:,:,3] = ...

are just modifying the 4th channel, i.e. the alpha/transparency channel of the image

Upvotes: 1

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