Image processing apparatus and image processing method

An image processing apparatus, comprising:

• a density distribution improvement module coupled to receive grayscale raw image data containing both first image information and second image information, said raw image data having a density distribution spanning from a low density side defining a first density distribution range to a high density side defining a second density distribution range, said high density side being higher than said low density side, said density distribution improvement module modifying the density distribution of the raw image data to shift the first image substantially to the low density side and to shift the second image substantially to the high density side, and generating grayscale improved image data;
• a threshold level calculation module coupled to receive the improved image data and calculate a threshold level for two-level digital conversion based on a density distribution in the improved image data;
• and
• a digitizing module coupled to receive the improved image data and the threshold level, digitize the improved image data using the threshold level, and output two-level image data.

An image processing method comprising:

• a density distribution improvement step for receiving grayscale raw image data containing both first image information and second image information, said raw image data having a density distribution spanning from a low density side defining a first density distribution range to a high density side defining a second density distribution range, said high density side being higher than said low density side, modifying the density distribution of the raw image data to shift the first image substantially to the low density side and to shift the second image substantially to the high density side, and generating grayscale improved image data;
• a threshold level calculation step for receiving the improved image data and calculating a threshold level for two-level digital conversion based on a density distribution in the improved image data;
• and
• a digitizing step for receiving the improved image data and the threshold level, digitizing the improved image data using the threshold level, and outputting two-level image data.