Image processing apparatus and method for discriminating whether document is color document or black and white document, image forming apparatus and facsimile machine including the image processing apparatus and a computer readable recording medium storing image processing program

摘要

An image processing apparatus includes a document conveying unit, an image reading unit, a gradient calculating unit, a gradient comparing unit and a document discriminating unit. The image reading unit scans a document conveyed by the document conveying unit in a scanning direction orthogonal to a conveying direction and detects pixel values of color components of each pixel. The gradient calculating unit calculates a gradient of the pixel value of each color component in the conveying direction for each pixel based on the detected pixel values. The gradient comparing unit compares differences of gradients among color components for each pixel and extracts the pixel where the graduent difference is below a threshold value. The document discriminating unit discriminates whether each pixel is color or black-and-white based on pixel values using discrimination criteria different for the specific pixels extracted by the gradient comparing unit and other pixels.