An image processing method includes generating a composite image of a selected image and sub-images. The crane is configured such that during crane operation, the moment generated by the counterweight unit acts on the rotating bed predominantly through the counterweight support frame. A trigger pull adjustment assembly is disposed between a second pivoting end of the sear bar and the trigger housing includes a trigger pull adjustment screw mounted in a threaded passage of the trigger housing, and a sear bar return spring abutting the trigger pull adjustment screw and inserted in a portion of the threaded passage of the trigger housing. After that, another heat treatment is implemented within an oxidizing atmosphere at a temperature higher than that of the previous heat treatment. The foregoing makes it possible to utilize effectively the display having a display area that is revealed when the display is pulled out.