Digital image forming apparatus having a function of compensating shadings using a white reference plate

An image forming apparatus, comprising:

• means for sequentially illuminating target areas while scanning said target areas;
• means for producing an image signal representative of the shade of darkness of areas obtained by sequentially illuminating the areas by said illuminating means starting with a first illumination, the target areas including a reference area of predetermined shade of darkness and an area of an original to be read;
• means for setting a light quantity of the illuminating means on the basis of the present image signals corresponding to the reference area so that said light quantity is in a proper light quantity during said first illumination of said illuminating means;
• means for storing sequential data representative of the image signals corresponding to light quantity previously obtained by said sequentially illuminating means;
• means for comparing present image signals with previous image signals stored in said storing means to obtain a difference between said present image signals and said previous signals;
• means for adjusting the light quantity of the illuminating means after a second illumination of said illuminating means such that said light quantity, when said difference falls within a set range, remains the same and is only changed to a proper light quantity by illuminating said reference area by said illuminating means when said difference is out of said set range;
• and
• means for forming an image on the basis of said image signals.

An image reading apparatus comprising:

• means for illuminating an original with light;
• means for producing an image signal by photoelectrically converting reflected light from said original by said illuminating means;
• means for converting said image signal into a digital image signal;
• means for forming an image on the basis of the digital image signal;
• first adjusting means for adjusting a light quantity of said illuminating means to be a predetermined value before said original is scanned, so as to read a reference material having a certain reflection factor with said light quantity of said illuminating means to obtain read data;
• first storing means for storing the read data obtained by said first adjusting means;
• means for comparing said read data stored in said first storing means with a reference value;
• second adjusting means for adjusting the light quantity of said illuminating means in response to a compared result of said comparing means;
• second storing means for storing said light quantity provided when said illuminating means is adjusted by said second adjusting means;
• and
• means for causing said second adjusting means to read said reference material with said light quantity of said illuminating means stored in said second storing means, causing said comparing means to compare said read data with said reference value, and causing said second adjusting means to adjust the light quantity of said illuminating means.