Volume Deformation correction

Sommaire

Automatic correction
Manual correction
Correction by the Diagonal
Correction type Horizontal / Vertical
Application of volume corrections to an image

Volume deformation is manifested by a change in the appearance of the components of the photo that are increasingly stretched towards the edges of the image. It is characteristic of a wide-angle lens usage and increases with the decrease of the focal length used. We usually start noticing below 28mm (24×36 format) and it becomes more and more visible later.

This distortion is cumulative with the other deformations related to the use of the wide-angle lens
* The distortion which is a specific characteristic of the lens by its construction
* The leakage effect of the vertical and horizontal planes depending on the rules of the perspective

This is not an optical defect. This deformation is normal on wide-angle pictures taken, and more with an ultra-wide angle lens. Its magnitude is a function of the distance between the point of view and the first planes framed when this distance is very small proportionally to the framed field. If we could look at a print (or a screen view) by positioning the eyes exactly in the same relative position as the camera when shooting (so very close, the nose stuck on it), we would not perceive any deformation. But we never look at an image like this because of the minimal distance necessary for normal vision.

* The choice between Diagonal and Horizontal / Vertical corrections determines the visual success of the correction depending of the photo content.
* The volume deformation is not linear. Null in the center of the image, it becomes more and more sensitive by moving away to become maximum on the edges of the image. The correction obviously takes it into account.

Comparison of the two corrections, crop off.
Since the skyline is located on the median horizontal axis of the image, it is not deformed by the Diagonal correction as well as the vanishing substantially joining the center. The other straight lines are more and more curved as we approach the edges. Horizontal / Vertical correction preserves the verticals of the deformation. But the perception of volumes is a little less good.

Comparison of the two types of corrections

Automatic correction

The Auto correction is the normal operation of this tool. ViewPoint directly assigns the correct correction value. It can be refined with the sliders but it is rare to return to it.

Unlike the automatic distortion correction, there is no requirement to have the corresponding optical module. To achieve this, ViewPoint simply needs to find the information it needs in EXIF metadata.

Manual correction

If there is no EXIF metadata (or if they are not correctly filled in), ViewPoint indicates it in the palette “Volume Deformation”. ViewPoint applies a standard correction.

Both possible cases in the absence of lens module.

Correction by the Diagonal

This is the most accurate. It starts from the center of the image with an amplitude that grows as it moves away from it. A representative case is the selfie photo..
It is particularly adapted to the subjects having spherical volumes in the broad sense (characters, heads, etc.). A representative case is the selfie photo.
On the other hand, it distorts the straight lines by bending them. The deformation is maximum for the lines along the edges of the frame.

– In palette “Volume deformation” – tool type “Diagonal”
The correction is automatic for the cases defined above.
The default value (150) is a complete correction. It can be decreased for a more natural rendering.

Illustration with a subject adapted to Diagonal type correction, placed at the edge of the frame. Focal length 21 mm (format 24×36).The real proportions of the subject are perfectly restored. The structured background was chosen to show the deformation undergone. It is always better to have a neutral background in terms of geometric shapes. In this example it is not very recognizable and of secondary importance.
For this type of correction, the magnitude of the induced deformations can lead to a severe reframing that should be anticipated at the shooting. This is not completely the case here where the headdress mounts on the top edge of the frame while keeping the original ratio. Moving to a free crop allows it to aerate slightly.PP

Correction type Horizontal / Vertical

The correction settles the image from the median vertical axis towards the edges for landscape format pictures (along the horizontal axis for portrait format pictures).
There is no curvature of straight lines. It is preferred for urban photography, monuments, interiors of buildings, etc.
It is not exact but better accepted on these types of subjects.

In case of doubt about the correction to be applied according to the subject, trying the rendering of the two types of corrections helps to determine the most adapted.

– In palette “Horizontal / Vertical” type “Volume distortion”
Here again the correction is automatic if ViewPoint can access the EXIF data.

– ViewPoint automatically presents the right choice according to the orientation of the original image.
In the case of a wrong proposition, the values 100 and 0 must be exchanged.
The values displayed are 100 by default for the selected correction direction (horizontal or vertical) and 0 for the other direction. This is an optimized correction for the majority of situations.
It is preferable not to modify (or very little) the correction to zero because of the antagonism between the two directions of adjustment.

A typical subject for this correction. Focal length 22 mm (format 24×36).The correction restores their normal appearance to elements near the edges. The problem that usually arises is the choice of cropping after correction.
Two options are possible: keep the maximum of the image area with a free crop, or lose a little by keeping the original ratio which is the solution chosen here, with a upward displacement to improve the cropping.PP

Beware of “the optical illusion”!
The default display of an image in ViewPoint (as in other software) is achieved by adapting the largest dimension of the image to the available display area. We can get the impression by applying the correction that it is done in the opposite direction to that expected.
For example, for a horizontal image like this, the display shows an image that keeps the same width and increases in height, while in reality its height remains fixed and its width decreases.
This can be verified by reading the dimensions displayed in pixels.

The good reflex if case of doubt is display the dual view: Before / After.

With PhotoLab, we can avoid this confusion by displaying the image at a fixed (zoom) size smaller than the display window.
Principle of correction Horizontal / Vertical and logical direction of corrections.PP

Application of volume corrections to an image

We often address the volume distortion correction at the end of the process. This position is well suited for images requiring diagonal correction. On the other hand, those with a Horizontal / Vertical type of correction are often subject to a correction.
This kind of correction is, in fact, a prerequisite for horizon and perspective corrections.

This is not contradictory with the operating principle of parametric software such as Photolab or ViewPoint where each setting can be made separately, and modified at any time before the final output. Some settings condition others.

Further corrections for a complete treatment. Focal length 17 mm in 24×36:On the final image, the cars in the foreground have returned to their normal proportions.