Usage: extract_focal()
When cropping, thumbor uses focal points in the image to direct the area of the image that matters most. There are several ways of finding focal points. To learn more about focal points, visit the :doc:`detection_algorithms`.
In order to use the extract_focal filter, the original image must be
a thumbor URL that features manual cropping. To learn more about manual
cropping, visit the :doc:`crop_and_resize_algorithms`.
Using the original manual cropping points, this filter adds the cropped area (originally in the format /LEFTxTOP:RIGHTxBOTTOM/) as a focal point for the new image.
For the new image, thumbor will use as the original the image URL that was the original for the segment with the manual cropping.
This means that for an URL like:
http://localhost:8888/unsafe/300x100/filters:extract_focal()/localhost:8888/unsafe/100x150:300x200/https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Turkish_Van_Cat.jpg/546px-Turkish_Van_Cat.jpg
Thumbor will use as original the following image URL:
https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Turkish_Van_Cat.jpg/546px-Turkish_Van_Cat.jpg
Original Image:
Cat's eye cropped:
http://localhost:8888/unsafe/100x150:300x200/https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Turkish_Van_Cat.jpg/546px-Turkish_Van_Cat.jpg
A bigger image based on above's crop with the extract_focal() filter:
http://localhost:8888/unsafe/300x100/filters:extract_focal()/localhost:8888/unsafe/100x150:300x200/https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Turkish_Van_Cat.jpg/546px-Turkish_Van_Cat.jpg
Without the filter that would be the result:
http://localhost:8888/unsafe/300x100/localhost:8888/unsafe/100x150:300x200/https://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Turkish_Van_Cat.jpg/546px-Turkish_Van_Cat.jpg
