The shadow is the connection of an object to a surface, not a decorative spot.
After changing the background, an object may be cut perfectly but still appear glued. The reason is usually lower: contact shadow has disappeared, direction has not coincided with light or softness does not correspond to the size of the source.
A believable shadow has three different layers.
It appears where a foot, shoe or product touches the surface. Without it, the object starts to hover.
Its shape is related to the silhouette, but stretches along the geometry of the floor or wall.
The larger and closer the source, the wider the transition from shadow to illuminated surface.
First, find the source for existing highlights.
Look at the light side of your face, the glare on the glass, shadows under your chin and folds. They set direction before a new background appears. If the window is drawn to the left and the face is illuminated on your right, you can't fix the contradiction with one beautiful shade.
The hardness of the shadow tells about the size of light
Sharp edge, sunlight or directional spotlight.
Soft border, but readable contact area.
Very smooth transition and low contrast.
The error occurs when the interior looks diffuse, and under the person lies a black shadow with a carved contour. Softness should coincide not with the object, but with lighting of the entire scene.
The shadow is rarely neutral-gray.
On the warm wooden floor, it gets a brown hue, on the green wall - a weak color reflex, while the shadow should not turn into a colored cast: it retains the texture of the surface and only reduces its brightness.
Request.Place the chair against the green wall. Save the light on the top left. Add a short, dense contact shadow under your legs and a soft main shadow to the right, with the texture of the floor inside. Don't change the shape of your chair or add a second light source.
Close the object with your palm and appreciate only light.
It is impossible to accurately restore light that can not be seen on any object.
If the source is flat and almost devoid of directional glare, the model chooses a plausible scheme itself. For a creative frame this is acceptable, but for a series of products it is better to fix one master with stable lighting.
Don't try to fix five contradictions with a single shadow. First, align the direction of light on the object and background, then contact, and only after that softness and color.
A good shadow is almost imperceptible, but without it the scene falls apart.
It doesn't have to attract attention. Its job is to confirm the height, position, light and surface material with one consistent signal.