What Are the Pixel Values in a Brand New Image.new() Image? (Pillow Explained)

[Rajeev Bagra]

ߓ Context (Initial Code)

When recovering a hidden black-and-white image using LSB steganography, we often create a new blank image and then fill it pixel-by-pixel:

from PIL import Image

def reveal_bw_image(filename):
    img = Image.open(filename)
    width, height = img.size
    pixels = img.load()

    secret_img = Image.new("L", (width, height))
    secret_pixels = secret_img.load()

    # later we fill it inside loops...
    return secret_img

This leads to a common beginner doubt ߑ

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✅ Q&A: What Are the Pixel Values in a Brand New Image.new() Image?

❓ Q: When we create a new image like this…

secret_img = Image.new("L", (width, height))
secret_pixels = secret_img.load()

…what are the pixel values at this point?

✅ Answer:
At this stage, the image is completely blank, and every pixel is set to 0 by default.

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❓ Q: What does pixel value 0 mean in "L" mode?

✅ Answer:
"L" means grayscale (black & white intensity image), where each pixel value is:

• 0 → black
• 255 → white

So when the image is created, it starts as a full black image.

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❓ Q: Why does Pillow set all pixels to 0?

✅ Answer:
Because Image.new() is creating an empty canvas.
Before we fill the pixels with meaningful values, Pillow initializes the canvas to a safe default:

✅ 0 (black) everywhere.

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❓ Q: How do pixels get meaningful values later?

✅ Answer:
Later in the program, the loop overwrites each pixel with recovered secret data, for example:

secret_pixels[x, y] = hidden_bit * 255

So the image changes from:

• completely black initially
  to
• a visible recovered hidden

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