Pixels and channels

An image is a grid of pixels. A colour image has 3 channels (red, green, blue), each 0 to 255.

• Shape is usually (height, width, channels), like (224, 224, 3).
• Greyscale has 1 channel.
• One 224×224 colour image is 150,528 numbers.

import numpy as np
img = np.zeros((224, 224, 3), dtype=np.uint8)
print(img.shape, img.size)

(224, 224, 3) 150528

Remember: Height comes first in the shape, then width.

Common mistake: Mixing up channel order: OpenCV loads BGR, most others use RGB.