Image Processing Reference
In-Depth Information
Image + Grid : This option illustrates the transformation as an
image in a grid with handles at the four corners. Additionally, a grid
appears in the transformation. Initially, the transformed image is
superimposed on the original.
Figure 3.15
The original size of the layer, the transformation frame,
and the clipped result
If you choose a grid option from the Preview drop-down menu, you can
select the number of grid lines and the grid spacing in the drop-down menu
under Preview.
The described tool settings are valid
for all transformation tools.
3.5.5 Removing Lens Distortion, Making
Perspective Corrections, and Reducing Vignetting
Even after correcting the perspective in the previous exercise, distortions and
warping still remain. This is due to the fact that the image was put together as
a panorama picture using several individual photos taken with a wide-angle
lens. In addition, the image has a left and a right vanishing point.
To correct these defects, GIMP offers the Lens Distortion and Curve Bend
filters. These filters provide not only perspective corrections, but also to a
certain extent corrective measures for barrel- and pincushion-shaped lens
distortions. If you wish, you could give your image the effect of a photo taken
with a fisheye lens (an extreme wide-angle lens). You can also reduce or
even eliminate vignetting. Basically, vignetting is the reduction of an image's
brightness or saturation at the periphery in comparison to the image center.
This effect often occurs when wide-angle lenses are used.
You can find the Lens Distortion and Curve Bend filters in the Filters >
Distorts menu.
Search WWH ::

Custom Search