Final answer:
If a photo with a white background is underexposed, the background will appear gray instead of white. This is due to insufficient light reaching the camera's sensor, and is not typically associated with the subject being overexposed or the absence of shadows.
Step-by-step explanation:
When a photo with a white background is underexposed, it means that not enough light has reached the camera's sensor. As a result, the white background will not appear bright and white as it should; instead, it will appear gray because it lacks the necessary light to be correctly rendered. This happens because the exposure variables such as shutter speed or aperture may be set to allow in too little light or because the ambient lighting is insufficient.
Underexposure doesn't typically cause the subject to be overexposed or washed out, and it doesn't prevent shadows from appearing. In contrast, underexposed images tend to be too dark, flat, and can have a loss of detail in the darker areas.
It's important in photography to balance the exposure to avoid both underexposure and overexposure to achieve the desired level of brightness and detail in both the subject and the background.