Correcting volume deformation with DxO ViewPoint
In collaboration with Gilles Théophile
Based on DxO Optics Pro’s exclusive technology, DxO ViewPoint lets you correct distortions and restore the natural proportions to your subjects in just one click. DxO ViewPoint corrects several geometric problems in images: distortion, perspectives (e.g., keystoning), horizon lines, and deformed subjects (notably people). We are going to concentrate on this last problem in this tutorial — in other words, we will discuss correcting volume deformation, a phenomenon that frequently confronts photographers who use wide-angle lenses.
To follow this tutorial, you will need:
- DxO ViewPoint.
- Photos in TIFF or JPEG format.
- You can download our demo images HERE.
1- What is volume deformation?
A common problem
All photographers who use wide-angle lenses, and particularly those who shoot group photos, know this problem all too well: no matter how tightly everyone is packed together, the people on the edges of the image invariably look distorted.
This distortion phenomenon, amplified by the use of short focal lengths and by proximity to the edge of the field, is called “volume deformation”.
Fortunately, volume deformation can be corrected by software, and here is where DxO ViewPoint comes in with its Volume deformation correction palette, which features two different corrections modes. The Diagonal correction is normally the one to use because it is the one that precisely responds to the distortions introduced by wide-angle lenses. However, the diagonal correction inevitably introduces distortion of certain straight lines in images, which is why in certain cases (as we will see in this tutorial), it can be better to apply a Horizontal/Vertical correction instead, which adequately restores subjects’ natural proportions.
2- Diagonal correction of volume deformation
It is preferable to apply the diagonal correction of volume deformation to all images. Here is a first example of this kind of correction.
2.1 – Select and open your image
To open an image in DxO ViewPoint, all you need to do is choose Open in the File menu.
When you open the application, the main window displays thumbnails of demo images that will help you visualize and correct the different kinds of deformation problems. Click on Open other file to browse your hard disk and open one of your own images.
A dialog box opens and prompts you to choose an image from your hard drive. Select the image you want to correct, and then click on Open to display it in DxO ViewPoint.
You can also use the keyboard shortcut Ctrl+O (PC) or Cmd+O (Mac), or simply drag and drop the image into the application’s main window.
2.2 – Automatically eliminate volume deformation with the diagonal correction tool
In this example, you can clearly see the deformation manifesting itself by a marked distortion of the young women’s arm.
Apply the diagonal correction by clicking on the icon in the Volume deformation palette.
After the correction is applied, the distorted elements regain their natural proportions.
The diagonal correction of volume deformation does not change the aspect ratio of the image, although the image will be slightly cropped; however, the image dimensions (i.e., its resolution) will also be slightly reduced.
2.3 – Manually adjust the correction if necessary
After the diagonal correction tool is activated, an Intensity slider appears in the Volume deformation palette.
By default, the Intensity slider is set at 150. If you increase the value, the correction will be stronger. Be careful, however, not to overdo the correction so as to lose the natural proportions of your subjects. You can also decrease the intensity if the correction seems excessive or if other distortion inevitably introduced by the volume deformation correction has become too noticeable.
Secondary effects of the diagonal correction
The Diagonal correction of volume deformation inevitably introduces some distortion because of certain optical laws. Such distortion will be particularly noticeable if your image contains straight lines, per the example below.
Let’s apply a diagonal correction to this image of a model that shows an obvious and unpleasant problem with volume deformation.
Although the distortion of the young woman has been perfectly corrected, the slats on the bridge are now curved because of the distortion introduced by the diagonal correction.
In this case, if you want to keep the horizontal lines straight, you will need to choose the Horizontal/Vertical correction of volume deformation discussed in the section below.
The diagonal correction does not affect the straightness of the straight lines going through the center of the image.
3- Horizontal/vertical correction of volume deformation
Although we have said that the diagonal correction is preferred, it will distort any straight lines in your image. In this case, to avoid such secondary distortions, you can choose instead the horizontal/vertical correction of volume deformation.
So here is how we will correct the preceding sample image:
3.1 – Select and open your image
To open an image in DxO ViewPoint, review step 1 in the second section (the diagonal correction of volume deformation).
3.2 – Apply the horizontal/vertical volume deformation correction
We saw before that the diagonal correction would not work very well for the image of the young woman on the bridge because of the straight horizontal lines. Let’s instead apply the horizontal/vertical correction of volume deformation by clicking on the icon in the Volume deformation palette.
This correction allows us to significantly reduce the distorted look of the young woman while keeping the slats on the bridge straight.
The horizontal/vertical correction will modify the aspect ratio of the image, because the image will be compacted laterally in order to restore the subjects’ natural proportions.
Horizontal and vertical lines will remain absolutely straight following the horizontal/vertical correction, but other lines will display a slight distortion.
3.3 – Manually adjust the correction if necessary
After the automatic correction is applied, the Volume deformation palette will display two new sliders, Horizontal and Vertical, which will allow you to precisely adjust the volume deformation correction.
By default, the Horizontal slider is set at 100 and the Vertical slider is at 0. If you find that the automatic correction is too much, you can reduce its effects by reducing the value of the Horizontal slider, which will increase the proportions in the image along the horizontal axis.
If the proportions don’t seem right to you along the vertical axis, you can increase the value of the Vertical slider so as to compress the image vertically.
As a general rule, the automatic corrections are sufficient for recovering the natural proportions of your subjects. Take care not to distort the image by overdoing manual adjustments.
4- Cropping and saving an image
4.1 – Automatically crop your image
Cropping is automatically applied by default when you apply a correction for volume deformation (horizontal/vertical or diagonal). The amount of cropping depends on the intensity of the correction required.
DxO ViewPoint displays the size of the image (height and width) in pixels on the bottom of the main window both before and after the correction.
By default, the tool is configured to freely crop the image while maximizing the field, but without taking into account the aspect ratio of the original image.
4.2 – Manually adjust the crop if necessary
After the automatic cropping is applied, you can adjust it manually. To do so, just select the crop tool by clicking on the icon in the Crop palette.
You can choose the aspect ratio that you want or simply keep the aspect ratio of the original image. After you select the tool, a frame will appear that you can move around within the image.
You can use your keyboard arrows to position the frame more precisely.
By default, the crop is limited to the “valid” part of the image, but you have the possibility of deactivating this option in order to freely crop the image. To do so, uncheck the Constrain to image box.
The edges of the corrected image are black, but you can use other software to fill in the missing parts of the image so as to maximize the visible field.
When you are satisfied with the crop, click on Apply. Your image is now corrected and cropped, and you can see the differences when comparing it to the original.
4.3 – Save your corrected image
When you are finished with correcting the volume deformation and with cropping, save your image by clicking on the icon in the toolbar, which will save the image as a new file. You can choose between JPEG and TIFF formats, name your image file whatever you’d like, and select the folder in which you want to save your image.
You can also choose Save or Save As in the File menu, depending on the action you want to take.
If you save your image in JPEG format, you can choose the compression level. The greater the value, the greater the quality (but also the file size).
Photos credits: Olivier Lambolez, Patrick Gaillardin