Document size detecting device using a plurality of thresholds

Claim 2

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light reflected from a document area, comprising: a photosensor which detects an amount of light reflected from a predetermined location of an area covered with the document cover; a first detector which detects a kind of the document; a second detector which detects whether the document is within said predetermined location by comparing an output value from said photosensor with a first threshold; a third detector which detects whether the document is within said predetermined location by comparing an output value from said photosensor with a second threshold different from said first threshold; and a controller which selects one of said second detector and said third detector based on a kind of the document detected by said first detector and which judges a size of the document based on a detection result of said selected detector.

Claim 3

A document size detecting device of claim 1, wherein said photosensor detects a color element of the document; and said first detector detects the kind of the document placed on the document table based on said detected color element.

Claim 4

A document size detecting device of claim 2, wherein said first threshold is used to detect a size of a monochrome document and is found by averaging a value for a white portion and a value for a black portion, and said second threshold is used to detect a size of a color document and has a smaller value than said first threshold.

Claim 5

A document size detecting device of claim 2 and further including a scanner which reciprocates said photosensor with respect to said document table, and wherein said photosensor detects the color element of the document when said photosensor moves forward with respect to said document table and detects placement of the document on the document table when said photosensor moves backward with respect to said document table.

Claim 6

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light reflected from a document area, comprising: a photosensor which detects an amount of light reflected from a predetermined location of an area covered with the document cover; a detector which detects whether a document is within said predetermined location by comparing an output value from said photosensor with a selected one of a plurality of thresholds, said selected one of said plurality of thresholds being selected based on a kind of the document placed on said document table; and a controller which judges the size of the document based on a detection result of said detector with said selected threshold.

Claim 7

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light reflected from a document area, comprising: a photosensor which detects an amount of light reflected from a predetermined location of an area covered with the document cover; a detector which detects whether a document is within said predetermined location by comparing an output value from said photosensor with a selected one of a plurality of thresholds, said selected one of said plurality of thresholds being selected based on a kind of the document placed on said document table; and a controller which judges the size of the document based on a detection result of said detector with said selected threshold.

Claim 8

A document size detecting device of claim 5, wherein said photosensor detects a color element of the document, and said selected threshold is selected in accordance with said detected color element.

Claim 9

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light from a document area, comprising: a photo image sensor which generates image data based on light reflected from a predetermined location of an area covered with the document cover; a first detector which detects a kind of the document; a pixel determining device which determines a pixel in the document area by comparing image data of the document from said image sensor with one of a first threshold and a second threshold; a controller which judges a document size by finding a boundary of the document area through confirming a certain number of successive pixels within said document area by said pixel determining device; and a switching device which selectively switches from said first threshold to said second threshold and from said second threshold to said first threshold based on a kind of the document detected by said first detector.

Claim 10

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light from a document area, comprising: a photo image sensor which generates image data based on light reflected from a predetermined location of an area covered with the document cover; a first detector which detects a kind of the document; a pixel determining device which determines a pixel in the document area by comparing image data of the document from said image sensor with one of a first threshold and a second threshold; a controller which judges a document size by finding a boundary of the document area through confirming a certain number of successive pixels within said document area by said pixel determining device; and a switching device which selectively switches from said first threshold to said second threshold and from said second threshold to said first threshold based on a kind of the document detected by said first detector.

Claim 11

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light from a document area, comprising: a photo image sensor which generates image data based on light reflected from a predetermined location of an area covered with the document cover; a threshold setting device for setting a first threshold and a second threshold, each being used for a different amount of the reflected light; a pixel determining device for determining a pixel in the document area by comparing image data of the document from said image sensor with one of said first threshold and said second threshold; a document size detector which detects a document size by finding a boundary of the document area through confirming a certain number of successive pixels within said document area by said pixel determining device; and a switching device which selectively switches from said first threshold to said second threshold and from said second threshold to said first threshold, wherein said switching device switches alternately between said first threshold and said second threshold every time a certain number of scanning lines in a scanning direction are completed by said image sensor.

Claim 12

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table and covered over with a document cover based on an amount of light from a document area, comprising: a photo image sensor which generates image data based on light reflected from a predetermined location of an area covered with the document cover; a threshold setting device for setting a first threshold and a second threshold, each being used for a different amount of the reflected light; a pixel determining device for determining a pixel in the document area by comparing image data of the document from said image sensor with one of said first threshold and said second threshold; a document size detector which detects a document size by finding a boundary of the document area through confirming a certain number of successive pixels within said document area by said pixel determining device; and a switching device which selectively switches from said first threshold to said second threshold and from said second threshold to said first threshold, wherein said switching device switches alternately between said first threshold and said second threshold every time a certain number of scanning lines in a scanning direction are completed by said image sensor.

Claim 13

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table based on an amount of reflected light, comprising: a first detector which detects an amount of light reflected from a predetermined location of said document table; a comparing device which compares an output value from said first detector with a threshold level in accordance with a detection result of said first detector; a changing device which changes the value of the threshold level based on a kind of the document placed on said document table; and a document size detector which detects a size of the document based on detection results of said comparing device.

Claim 14

A document size detecting device employed in an image forming apparatus for detecting a size of a document placed on a document table based on an amount of reflected light, comprising: a first detector which detects an amount of light reflected from a predetermined location of said document table; a comparing device which compares an output value from said first detector with a threshold level in accordance with a detection result of said first detector; a changing device which changes the value of the threshold level based on a kind of the document placed on said document table; and a document size detector which detects a size of the document based on detection results of said comparing device.