“Is your image overexposed, call it hi-key…”. A phrase that can be regularly found on the internet. I absolutely do not agree, as there is a major difference between the two. The sole fact that a background may be completely white does not make an image overexposed. You’ll have to look at the subject: is the subject also washed out, then you can call an image overexposed. Is the subject well exposed, but does the image consist of mainly light and white tones, then you have found yourself a hi-key image.
Hi-key is often the result of specific weather circumstances, mainly lightgrey skies. If you shoot a subject against such a sky (or the reflection of that sky in still water), you’ll have to add lots of light to the metered exposure in order not to underexpose the subject. Given the limited dynamic range of the camera sensor, the background (sky or water) will then render a pure white. Nothing wrong with the exposure (in fact, it could not be better!), just a result of the existing circumstances.
The image to the left of a juvenile Moorhen was taken at the Oostvaardersplassen. A long way from home to shoot a Moorhen, but I was there to sell my beloved Tamron 90mm and buy a Sigma 150mm.
Juvenile Moorhen; Canon 1D Mark III w. 500/4 IS and 1.4x; 1/200s at F5.6 and ISO 400; Handheld