New Liquid Rescale tool under construction...
Since few weeks, an active work have been done with Julien Pontabry and Julien Nardoux to solve this bug report.
On preview screenshots, you can seen a picture resized horizontally to 150%. A preservation mask in green is drawn over the image part to not touch elements during transformation. see below, another example with two area to preserve:
Look like houses are not deformed when image is scaled up horizontally. All the rest of image contents will be transformed. You can created nice banner for web site with this tool for example. Now, another try with a suppresion mask to remove unwanted contents:
With this picture, the kid on the middle will be removed using a suppression mask draw over in red. My son on the bottom must be preserved during transformation. Suppression mask only work for the moment to reduce size of image. With this example, width is scaled down to 80%.
And the last sample. Yes this one is under Windows Vista ! And it's run fine too, as under Linux...
Liquid Rescale tool will be available in digiKam 0.11.0. Some work need to be done to improve mask creation, and polish settings view to be more ergonomic.