An image pixel is the smallest unit that forms a digital picture. It is like a tiny dot that has a specific color or brightness. Many pixels together make up the complete image that you see on a screen or print. Full definition
The gray scale describes how the brightness of image pixels varies between the black and white extremes and determines the contrast within an image. (displaymate.com)
The gray scale describes how the brightness of image pixels varies between the black and white extremes that were discussed in Table 2. (displaymate.com)
This creates a single image pixel that can be viewed from all sides. (sciencenews.org)