Shadows, and the trap in them

A product cut out and placed on pure white looks wrong in a way most people notice without being able to name: it floats. A shadow fixes it in seconds. It also introduces the one failure that can break a pure-white requirement without you seeing it happen.

Why the cutout looks pasted on

A photograph carries evidence of where the object sits — a contact shadow, a slight darkening under the base, a reflection. Remove the background and all of that evidence goes with it, leaving an object with a perfectly hard edge and no relationship to the surface it is supposedly on. The eye reads this instantly as a composite. Adding back a soft shadow under the base restores the one cue that matters most, which is contact: the point where the object meets the ground. That is why a *contact* shadow — short, close, under the base — is more convincing than a long dramatic one.

What makes a shadow look right

The defaults here are deliberately restrained: the shadow is squashed to **14%** of the product's height, spread slightly wider than the product at **1.04×**, lifted **1.2%** off the base so it does not read as a hard line, drawn at **28% opacity**, and blurred by **5%** of the product's width. Restraint is the whole point. The most common mistake is a shadow that is too dark and too far away, which does not read as contact at all but as a second object. If you can see the shadow before you notice the product, it is wrong.

The edge-bleed trap

This is worth the section on its own because it was caught in a real browser rather than reasoned about. A blurred shadow does not stop at its nominal radius — a canvas blur is a Gaussian, and the visible tail reaches roughly **2.6×** the radius. With the fill pushed high, that tail reached the bottom edge of the frame and pulled the background pixel there down to 229. The frame still looked white; the pure-white claim was false. The fix is that the bottom and side clearances are now computed from how far the shadow can actually reach, and because the shadow is wider than the product, the whole composition is scaled to fit when the fill approaches 100%. It is a good example of why measuring beats assuming: 1.8× was the theoretically tidy number, and it was wrong.

When to leave the shadow off

Turn it off when the marketplace demands pure white and you are pushing the fill high, if you would rather have the extra size than the depth cue. Turn it off for flat products photographed from directly above — a print, a phone case, a sheet of stickers — where there is no contact point to suggest and a shadow just looks like a mistake. And turn it off for anything that will be composited later, since the person compositing wants a clean cutout and their own lighting, not yours.