Shading correcting method and shading correcting apparatus for use in image forming apparatuses

摘要

There is provided an apparatus capable of correcting a threshold value for a white reference value and a white reference value correcting value if a white reference plate becomes dirty to calculate a white reference value corresponding to the dirt of the white reference plate and consequently, capable of making good shading correction using the white reference value. If the density value of any one of pixels of line data is higher than a threshold value WMAX1, the threshold value WMAX1 is made high, and a white reference value correcting value WDN is made high. As a result, even if the white reference value is corrected when the white reference plate becomes dirty as a whole, only a value obtained by the correction is not extremely low because the white reference value correcting value is high, thereby to make it possible to obtain a suitable white reference value. Accordingly, shading correction based on a good white reference value can be made, thereby to make it possible to obtain a good shading-corrected image.