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55 lines
2.1 KiB
Markdown
55 lines
2.1 KiB
Markdown
---
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title: Manipulate image pixels in Python
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layout: post
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excerpt: I had a black and white image but I wanted a black image with the white bits transparent.
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thumbnail: /assets/blog/manipulate_pixels.png
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social_image: /assets/blog/manipulate_pixels.png
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assets:
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alt:
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image_class: invertable
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---
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The way I've implemented dark mode on this site is to mark some images with a class `invertable` that means they still look good inverted. And then in CSS I go ahead and invert them if you're in dark mode. For other images I just dim them a bit.
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<figure class="two-wide">
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<img src="/assets/blog/micropython/simulated_display.png" class="invertable">
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<img src="/assets/blog/micropython/simulated_display_transparent.png" class="invertable">
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<figcaption>Try switching back and forth between dark mode and light mode, the one on the right works, the one on the left gets and ugly black background.</figcaption>
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</figure>
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However for some images like this black and white png it looks a bit weird when inverted because the background becomes hard black but my site's background is a dark grey. So I wanted to make the white pixels transparent instead.
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Anyway the point of this post is that I knew in terms of pixel values what I wanted to do but wasn't sure how to do this in an image editors. So here's the code for you and my future reference:
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```python
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import sys
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import numpy as np
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from PIL import Image
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if len(sys.argv) < 3:
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print("Usage: python convert_to_transparent.py <input_image_path> <output_image_path>")
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sys.exit(1)
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input_path, output_path = sys.argv[1], sys.argv[2]
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grey = np.array(Image.open(input_path).convert("L"))
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alpha_channel = 255 - grey
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rgba_array = np.zeros((grey.shape[0], grey.shape[1], 4), dtype=np.uint8)
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rgba_array[..., 0] = 0 # Red channel
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rgba_array[..., 1] = 0 # Green channel
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rgba_array[..., 2] = 0 # Blue channel
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rgba_array[..., 3] = alpha_channel # Alpha channel
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# Create a new image for the output
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rgba_img = Image.fromarray(rgba_array, mode="RGBA")
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# Save the result
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rgba_img.save(output_path, "PNG")
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print(f"Image saved to {output_path}")
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```
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