Image forming apparatus which avoids copying insignificant information

An image forming apparatus, comprising:

• means, having a light source, for illuminating an original document in a scanning direction;
• means, having an optical system, for focusing a reflected light beam from the original document;
• first converting means, including a photoelectric transducer, for converting optical image data formed by the focusing means into an electrical analog signal;
• second converting means for converting the electrical analog signal obtained by the first converting means into a plurality of digital image signals, said digital image signals corresponding to a plurality of portions of the original document, and representing image density levels at said portions, respectively;
• means for forming an image on a medium on the basis of said digital image signals;
• means for temporarily storing said digital image signals;
• means for computing a variation rate E based on the digital image signals stored in said temporarily storing means, said variation rate E being a variation rate of the image density levels represented by the digital image signals obtained by subtracting image density level values of nearby pixels from one another;
• means for deciding whether or not an image forming operation by the image forming means should be interrupted when the variation rate E is lower than a threshold value T, said threshold value T being a reference value used for determining whether or not the original document has an image thereon;
• and
• means for causing the image forming means to interrupt the image forming operation when the deciding means decides that the image forming operation should be interrupted.

An image forming method, comprising the steps of:

• scanning an original document in a scanning direction to optically obtain images corresponding to a plurality of portions of the original document;
• converting the images into a plurality of image signals representing image density levels;
• computing a variation rate E based on the image signals, said variation rate E being a rate of an image density variation represented by the image signals obtained by subtracting image density level values of nearby pixels from one another;
• determining whether or not an image forming operation, by which an image is formed on a medium on the basis of the image signals, should be interrupted when the computed variation rate E is lower than a threshold value T, said threshold value T being a reference value used for determining whether or not the original document has an image thereon;
• and
• informing an operator of determination that the image forming operation should be interrupted.