Many elements and subjects can be identified from their outline itself. In order to achieve this successfully in a photograph, the camera angle needs be chosen carefully. From some angles, a two-dimensional shape simply won’t be as recognisable as from others. A cat or a dog, for example, is more identifiable from the side than from the front. A temple or a mosque would be identified better as a silhouette against the light if shot from a lower angle as more of the shape would overlap the sky.
Unlike other subject elements, like form, the lighting angle is not particularly important for accentuating shape. Backlighting works quite well, because with the right exposure ( generally towards the under exposure ) one can get a silhouette that shows as an isolated shape. However, frontal lighting can work just as successfully. The important factor to include is a strong contrast between the subject and the background. This can be a contrast in brightness, as with a silhouette, but a contrast in color can work equally well in defining the outline.
While the photograph on the top of this page only reveals the shape, the nudes above reveal the form as well besides the shape. This is dues to the back light spilling over the subject and revealing the three dimensionality of the form as well to some extend. If the light was shifted more towards the side than towards the back, more of the form would be apparent.
When shooting silhouettes, the camera must be made to expose for the background, not the dark foreground. A camera with an older metering system would do so by default as it would measure the light. This can be done by using exposure compensation to underexpose the shot but this will work only if there is a situation with a bright background and a relatively darker subject. You may use spot metering to take a reading from the backdrop and lock that exposure. However, be care full that you do not spot meter the subject as that will reveal the detail in the subject rather than rendering it as a silhoette. Look at the results on screen carefully after each shot and reshoot if the background appears overexposed, or if the subject is not dark enough. When you’ve got it right, the exposure histogram, if your camera provides one, should show the graph bunched up toward the left-hand side of the screen. If in doubt, you can always bracket your shots more towards under exposure.
Camera angle plays a very important role in revealing shape. Every shot revealing shape or outline does not necessarily be a silhoette.
However, frontal lighting can work just as successfully. The important factor to include is a strong contrast between the subject and the background. This can be a contrast in brightness, as with a silhouette, but a contrast in collour can work equally well in defining the outline.
It does not have to be restricted to human forms, in the landscape above, shot from a boat around the Phi Phi islands the huge rocky mountain shows its dominating shape against the cloudy evening sky. Notice the tiny white boat in front.