Image display device, image display method, image display program, and computer-readable recording medium whereon program is recorded

An image display device including a display unit configured to display an image in an image display area on a display screen and an input unit configured to receive an instruction input indicating a position on the display screen, comprising:

• an acquisition unit configured to acquire position information indicating a position of an instruction input received by the input unit;
• a region recognition unit configured to specify an enclosed region in the image display area enclosed by a trajectory indicated by a set of position information received by the acquisition unit based on sequential instruction inputs through the input unit and recognize the enclosed region as a selected region;
• a direction specifying unit configured to specify a direction of the trajectory enclosing the enclosed region based on the trajectory of the position information received by the acquisition unit;
• a determination unit configured to determine a zoom-in ratio of an image displayed in the image display area when the direction specified by the direction specifying unit is a first direction, and determine a zoom-out ratio of an image displayed in the image display area when the direction specified by the direction specifying unit is a second direction opposite to the first direction, based on a range of the image display area and a range of the selected region recognized by the region recognition unit;
• and
• a display control unit configured to cause a zoomed-in image obtained by zooming in the image displayed in the image display area with the zoom-in ratio determined by the determination unit to be displayed in the image display area with a center of the zoomed-in image and a center of the image display area coinciding with each other when the direction specified by the direction specifying unit is the first direction, and causes a zoomed-out image obtained by zooming out an image at least partly including the image displayed in the image display area with the zoom-out ratio determined by the determination unit to be displayed in the image display area with a center of the zoomed-out image and a center of the image display area coinciding with each other when the direction specified by the direction specifying unit is the second direction, wherein
• when position information based on sequential instruction inputs following the sequential instruction inputs related to specifying the enclosed region is additionally acquired by the acquisition unit after specifying the enclosed region by the trajectory of the position information, the region recognition unit acquires a trajectory of the position information received after specifying the enclosed region, and
• the determination unit adjusts the zoom-in ratio or the zoom-out ratio of the image displayed in the image display area based on a position and a length of the trajectory of the position information received after specifying the enclosed region acquired by the region recognition unit.