Hello
I find Capture One to be the most intuitive and friendly post processing software, However there is still room for improvement.
My understanding of Keystone (the tool with four handles) is that after applying the transformation, the handles should align to a rectangle with horizontal and vertical sides.
This works for minor distortions, e.g. when the plane of the sensor is only off by a small angle from the plane of the rectangular subject being rectified.
When the plane of the sensor is off by a large angle (for instance when photographing a glass framed image in a severely slanted fashion to avoid unwanted reflections, with the intent to rectify the frame in post) Keystone often does not completely rectify the image. In other words, the Keystone handles form a trapeze rather than a rectangle after applying the transformation. This forces the user to use an alternative method such as DxO ViewPoint.
I suggest adding this fix to the wishlist for future versions of Capture One. I do understand that applying severe rectifications to an image may cause a loss of quality in the areas of the images that are highly magnified by the transformation. But it is up to the user to decide whether or not to rectify an image. There is no theoretical reason why severe transformations cannot be calculated. I suspect the algorithm used in Capture Pro's Keystone is faulty because it decomposes the transformation into a rotation and a differential stretching, rather than applying a single matrix transformation.
Since this is about adding a fix to the wishlist, I have two additional suggestions:
Consider turning the Keystone handles into Loupes, locally magnifying the image under them, when they are moved, to facilitate the precise positioning of the handles. This is similar to how DxO ViewPoint works.
Also, consider making it easier to find the corners of the canvas when using the Crop tool. For dark images, one has to hover the mouse around to hunt for the corners of the canvas.
I believe that these fixes and enhancements would be particularly welcome by your users that do interior or architectural photography.
Keep up the good work!