One of the challenges of photographing the real world is that a three-dimensional scene is reproduced in a two-dimensional image. As a result, three-dimensional objects that are not on the optical axis of the camera can appear stretched out. The steeper the angle at which rays from the subject reach the lens, the greater the apparent error — hence these phenomena are particularly noticeable with wide-angle lenses. This stretching becomes even more objectionable the nearer the objects are to the edges of the frame. Volume anamorphosis (sometimes referred to as wide-angle stretching or shape stretching) is occasionally desired as part of a photographic effect, but mostly it has been tolerated as simply inevitable.
The volume anamorphosis correction has to be user-set, as it is completely photo-content-dependent. Once it is selected, DxO Optics Pro performs the correction automatically.
DxO Optics Pro allows you to control for the two most typical cases in which volume anamorphosis has the strongest visible impact, while taking into account the relevant factors (lens type, focal length, and position in the field) to help you adjust your image.
1. Choose cylindrical correction to preserve picture components whose curvature is mainly in one direction (such as standing figures, bottles, buildings, trees or architectural columns)
Cylindrical shapes near the edge of the image frame no longer appear thicker; monuments are straightened and retain their original proportions; and bodies keep their normal weight!
2. Choose spherical correction for elements with a similar degree of curvature in all directions (such as the human head, tennis balls, apples and oranges)
3. These corrections are indispensable for wide-angle portrait, social, wedding, and architectural photography
Whereas cylindrical correction was applied in the above case, there are fewer important straight lines in the semi-circular arrangement of the group of figures below, to betray the geometric distortion. However, the figures’ heads (which are fundamentally spherical) appear stretched near the edges of the image. Using spherical volume anamorphosis correction this time produces a more natural result.
Lens design is always going to remain a trade-off between correcting for optical distortion and correcting for volume anamorphosis, which are different but related image geometry phenomena.(1)
4. Easily find your ideal balance between volume proportion and geometric accuracy
The initial photo of the bridge was taken with a fisheye, which, despite the strong distortion, has preserved the proportions of the figure on the right and of the lamp-posts well. In the center image, geometric distortion has been corrected, but the figure on the right of the frame and the lamp-posts appear unnaturally ‘fat’ due to volume anamorphosis. In the third image, cylindrical volume anamorphosis correction has restored the lamp-posts' and figure’s natural proportions.
(1)This fact - that the laws of physics just don’t allow us to have our cake and eat it too - is reflected in lens design. Fisheye-type lenses have huge distortion but very limited volume anamorphosis. Rectilinear lenses display much more limited (though very visible) distortion and very visible volume anamorphosis.