The same image rendered with different os/hardware will almost always look different. Different operating systems and monitors have different default gamma cur

The same image rendered with different os/hardware will almost always look different. Different operating systems and monitors have different default gamma curves for rendering brightness and black levels. Monitors are most likely either uncalibrated, or _can't be calibrated_ to render a greyscale with just 64 brightness levels distinctly. TFA is calling attention to "posterization" in their portrait backgrounds. They expected the grey background to have a smooth gradient, but, depending on your monitor, you should see visual jagged stair-steps between different grey levels. When an image uses a color palette that's insufficiently variable to render the original image colors with high fidelity, that's "posterization." (I paid for my college doing high-end prepress and digital image services, and got to work with a ton of really talented photographers who helped me see what they were seeing)