But one of the problems of creating thumbnails, and this is true of timthumb as well, is that if your different image sizes have different aspect ratios, then the crop that is generated doesn’t always look great.
Problems with WordPress Image Editor
The WordPress image editor allows you to create a crop of your orginal image, but it only changes the deafult WP images sizes (thumb, medium, large etc) and doesn’t touch the custom sizes that themes like Xi rely on. The “save all sizes” option does not change the custom sizes. It is a little confusing, but it is only when you regenerate your thumbnails using a plugin or individually in the Media section of the dashboard are your images resized/cropped.
This is clearly a limitation of the current release of WordPress and perhaps it will be improved.
Use the Post Thumbnail Editor Plugin
This limitation has not gone unnoticed. We have come across one awesome plugin that allows you to create indivudally cropped images for each image size in your theme.
The tool is accessible from inside the Media section of the dashboard or from inside the Insert Media dialog. Clicking thumbnails brings up an interface that lets you manage your thumb edits.
This works pretty well, but be warned that if you at a future point, regenerate your thumbs, you will loose the individual crops.
But for now this is a really useful tool, for those looking for perfect crops in their thumbs.