Pixels are the basic building blocks of an image (word pixel stands for “pixel element”). Most cameras capture square pixels (there are also rectangular pixels).

Imagine an image as a brick wall and pixels as its bricks:

As every wall, image can have different “thickness” – depending how many pixels-wide it is: double, triple, multiple.. On this particular example the wall is three-pixels-wide.

Number of the pixels in the depth of the wall are channels.

And number of those are determined by the color space (with this example, the color space is RGB which has red, green and blue channel).

The size of the pixel is controlled by the resolution.

Each pixel has an uniform colour. How specific is the colour (8-bits, 16-bits, 25-bits, 32-bits.. of information) depends on the number of colours available – bit depth. For example: there can be only two colours available (white, black), 256 colours..

Conclusion. The more pixels and the higher the bit-depth of the pixels, the more information there is available and the higher quality the image is.