Relative Image Size in Digital Photography

With an only point of view, the main information about the depth is provided by the relative size of the images. The size of an objects image depends in first place on it's real magnitude and in second place on the distance it is from us. Let's image, for example, a three-dimensional cubic object. All it's edges are equal, but nonetheless, when observing it from an oblique point of view, we see the vertical edge which is closest appears larger than the vertical edge we see, for example, at the left, because it is a little farther. The difference in apparent size of two edges informs us of the volume of the object, of it's depth and of our position regarding it.

Now we see the cube maintaining the observation direction but reducing the distance in half; this increases the size of the image and the two corners appear larger now. Nonetheless, we can be sure that the difference in the size of the two considered edges isn't proportionally equal to the earlier case, but has increased . Regarding the observation distance, which has been reduced, the greater proximity of an edge is now more relevant, and it's image is comparatively much larger than the other: the size of the image of the first has increase proportionally more than the size of the second image. Therefore the exit lines are highlighted, as is the depth perception.

When we are close to something, we perceive it's volume and relief better because the depth sensation is accentuated by the great variation of relative sizes of images. Small differences in depth can be perceived because these are relative regarding the observation distance.

An example, this time photographic: lets suppose we want to make a portrait in first plane. If we want the face or head of a person to fill the image and we have a normal lens, it would be very hard to get a favorable photograph. Why? Because we have to get to close . When we are too close to the face, the nose remains, in regard to the total distance, a lot closer to the camera than the ears; therefore, the image of the nose regarding the rest of the face will be greater than we consider normal, this feature will appear exaggeratedly large. If we want to do a portrait were the face completely fills the image using an angular, we'd have to get so close the effect would be like a cartoon.

Let's go back to the cubic object and now lets suppose that, maintaining the observation direction, we double the distance regarding the first point of view. The size of the images reduces and it is easy to demonstrate the difference between the size of the image of the closest edge and that of the furthest away is proportionally smaller than in the first case. Regarding the total distance, now increased, the greater proximity of an edge regarding another is less relevant because of what refers to the difference between the sizes of it's respective images. The exit lines are softened and the depth sensation softens.

When we are far from something, it's depth is less apparent because the information that the variation in relative sizes is reduced; the differences in depth are less relevant regarding the observation distance. Therefore, the other dimensions are reinforced and, in the distance, things acquire a flatter aspect, were the shape and outline predominates over the volume.