Image processing method and image processing apparatus

An image processing method wherein analog density values obtained from a sensor, which detects a density value of image data for each picture element, are converted Into digital density values by analog to digital conversion means, which converts analog density values obtained from said sensor into digital density values of a fixed number of bits for a conversion density range, and the digital density values thus obtained are compared for the individual picture elements with a threshold level to convert each of the digital density values into one of two binary values of white and black, comprising the steps of:

• producing a histogram of density values of a noticed picture element and picture elements around the noticed picture element;
• modifying the conversion density range of said analog to digital conversion means in response to a density range of a peak appearing in the histogram;
• and
• converting, by said analog to digital conversion means, an analog density value of the noticed picture element into a digital density value using a scale obtained by dividing the modified conversion density range by a number provided by the fixed number of bits.

An image processing apparatus, comprising:

• a sensor for detecting a density value of image data for each picture element:
• analog to digital conversion means for converting analog density values obtained from said sensor into digital density values of a fixed number of bits for a conversion density range;
• binary digitization means for comparing the digital density values from said analog to digital conversion means for the individual picture elements with a threshold level to convert each of the digital density values into one of two binary values of black and white;
• histogram production means for producing a histogram of density values of a noticed picture element and picture elements around the noticed picture element;
• setting means for setting a conversion density range for the noticed picture element in response to a density range of a peak appearing in the histogram produced by said histogram production means;
• and
• conversion means for converting the digital density value of the noticed picture element from said analog to digital conversion means into another digital density value using a scale obtained by dividing the conversion density range set by setting means by a number provided by the fixed number of bits.

An image processing apparatus, comprising:

• a sensor for detecting a density value of image data for each picture element;
• analog to digital conversion means for converting analog density values obtained from said sensor into digital density values of a fixed number of bits for a conversion density range;
• conversion density range setting means for setting the conversion density range of said analog to digital conversion means;
• binary digitization means for comparing the digital density values from said analog to digital conversion means for the individual picture elements with a threshold level to convert each of the digital density values into one of two binary values of black and white;
• histogram production means for producing a histogram of density values of a noticed picture element and picture elements a-round the noticed picture element;
• and
• conversion density range modification means for modifying the conversion density range set by said conversion density range setting means in response to a density range of a peak appearing in the histogram produced by said histogram production means.