Rotations--Again

[Robert Schleif]

Because a beginner to PWP might expect to find the ability to rotate an image by any amount in the Rotations and Reflections transformation, it might be worthwhile to add this capability there.

The ability of the Crop transformation to rotate an image is easily overlooked, but could be made more prominent by placing the Angle box under the heading Rotation which could be placed at the far left of the transformation window.

When an image is being rotated by Crop, new pixels not within the original image area but which are within the new image border are created and made black. Therefore, new pixels outside the original image area are "acceptable". However, the transformation only permits you to move inward the lines defining the crop. Moving them outward, which would need new pixels and which would create borders, is blocked. Why allow new pixels for an image when you rotate, but not otherwise? Why not let the lines defining the crop to move anywhere? Thus, you could crop and/or add borders from the same transformation. The color of the added pixels could be handled as it is in the Add Border transformation. Call it the Crop/Border transformation.

[tomczak]

You could use Level with Crop to Include Entire Image option to rotate the image without cropping the corners - the added canvas will be black, but you can easily change it to your liking with e.g. four shift-clicks of Fill Tool.

You could also do a similar thing with Warp/Rigid, using the Scale Factor 1:1 to reduce resampling, and you can add margins of any size to the rotated (or not rotated) image, although you can't specify the exact value of the rotation angle.

[jsachs]

Rotations by 90 degrees plus reflections are a common special case of rotations that avoid all the problems of out-of-bounds pixels and can be executed very quickly without any resampling. Mixing in rotation by an arbitrary angle would bring in all of these additional issues and would make the dialog box significantly more complicated. The help file does refer users to the other methods for rotating images by an arbitrary angle.

If Crop let you move the crop box outside the image, it would become a great deal harder to crop unrotated images right to the edge without picking up some black background. Personally, I do not use this method to rotate unless I am cropping anyway and want to make a small adjustment to level the image at the same time. The Level transformation is better for rotating most of the time since it lets you accurately level the horizon or get trees and buildings to stand up straight, and it automatically trims the border.

[Robert Schleif]

To make it easier for a novice seeking to rotate an image, the Crop transformation could be named Crop/Rotate.