Image forming apparatus and method of controlling the same

A method of controlling an image forming apparatus comprising:

• generating and storing a first pre-scan image and a first main scan image through a first scan task according to a first scan command;
• generating and storing a second pre-scan image through a second scan task according to a second scan command;
• determining whether a document at the first scan task is replaced by a new document for the second scan task by comparing the first pre-scan image with the second pre-scan image;
• and
• using the first main scan image as a result of the second scan command without performing the second scan task according to the second scan command upon determining that the document at the first scan task is not replaced by the new document.

An image forming apparatus comprising:

• a scanning device to scan a document;
• a manipulation device to generate a first scan command and a second scan command;
• a storage unit to store a first pre-scan image and a first main scan image generated from a first scan task according to the first scan command and a second pre-scan image generated from a second scan task according to the second scan command;
• and
• a display unit to display the first pre-scan image and the second pre-scan image;
• and
• a control unit to determine whether a document at the first scan task is replaced by a new document for the second scan task by comparing the first pre-scan image with the second pre-scan image, and control the scanning device so as to use the first main scan image as a result of the second scan command without performing the second scan task according to the second scan command upon determining that the document at the first scan task is not replaced by the new document.