Image processing apparatus

A method for detecting a document comprising the steps of:

• reading a document put on a document setter, having an image reading area on which a document to be read is put;
• extracting edges of the document based on image data obtained by reading the document put on the image reading area;
• obtaining lines of the document from the extracted edges;
• determining edges along a longest line among the obtained lines of the document obtained from the extracted edges;
• and
• determining a slope of the document put on the document setter based on the edges along the longest line.

An image forming apparatus comprising:

• a document setter, having an image reading area on which a document is put;
• an image reader which reads the document put on said document setter;
• a detector which detects a document area of the document in the image reading area based on image data of the document read by said image reader;
• a means for determining a rectangular area which includes the detected document area, said means for determining a rectangular area being adapted for determining a rectangular area even in the case when the document extends beyond the image reading area;
• a means for determining a slope of the rectangular area;
• a rotator which rotates the image data included in the rectangular area to correct a tilt of the document;
• and
• a printer which forms an image on a paper based on the image data rotated by said rotator.

A method for detecting a document comprising the steps of:

• reading a document put on a document setter, having an image reading area for reading a document which is put in the image reading area, by moving a scanner in the subscan direction for reading an image with a line sensor aligned in the main scan direction;
• extracting edges of the document based on image data read from the document;
• determining, from the extracted edges, edges of lines having slopes equal to or smaller than a predetermined angle relative to the subscan direction in the extracted edges;
• and
• determining a tilt of the document put on the document setter based on the determined edges of lines;
• wherein in the step of determining the tilt of the document, the slope of a longest line in the lines having slopes equal to or smaller than the predetermined angle relative to the subscan direction is determined as the tilt of the document.