Abstract In a data processor, image data of a pixel matrix is subjected to orthogonal transformation to coefficient data, the coefficient data is quantized with a first quantization table for character image and a second quantization table for half-tone image, and the image data is discriminated to be character image data or half-tone image data according to the quantization data. The selected data is then coded. In another processor, image data are divided into first and second processing blocks of m*m and M*M pixel matrices wherein M>m and the second processing block includes one of first processing blocks and adjacent pixels. Image data in a first and second processing block are subjected to orthogonal transformation to coefficient data. It is discriminated according to the coefficient data of the second processing block if the image is a character, dot, or half-tone image to select an appropriate quantization table, and image data of the first block is quantized according to the selected table and the quantized data are coded. In a further processor, two discrimination windows are provided, the first having coefficient data around the DC component and the second having the other data. Orthogonal transform coefficients of image data in a processing block are calculated, and maximum of absolute values in the windows are obtained. An image is discriminated to be a dot image if the maximum of the first window is larger than the second and larger than a threshold value.
A data processor comprising: an orthogonal transformation device for performing orthogonal transformation of an image data of a prescribed pixel matrix to coefficient data; a first quantization device for quantizing the coefficient data received from the orthogonal transformation device with a first quantization table for character image; a second quantization device for quantizing the coefficient data received from the orthogonal transformation means with a second quantization table for half-tone image; a discrimination device for discriminating if the image data is a character image data or a half-tone image data according to first quantization data quantized by said first quantization device and second quantization data quantized by said second quantization device; a selector for selecting the first quantization data or the second quantization data according as said discrimination means discriminates that the image data is a character data or a half-tone image; and a coder for performing entropy coding on the quantized data selected by said selector.
Claim 2
Dependent Claim
156 words
A data processor comprising: an orthogonal transformation device for performing orthogonal transformation of an image data of a prescribed pixel matrix to coefficient data; a first quantization device for quantizing the coefficient data received from the orthogonal transformation device with a first quantization table for character image; a second quantization device for quantizing the coefficient data received from the orthogonal transformation means with a second quantization table for half-tone image; a discrimination device for discriminating if the image data is a character image data or a half-tone image data according to first quantization data quantized by said first quantization device and second quantization data quantized by said second quantization device; a selector for selecting the first quantization data or the second quantization data according as said discrimination means discriminates that the image data is a character data or a half-tone image; and a coder for performing entropy coding on the quantized data selected by said selector.
Claim 3
Dependent Claim
25 words
The data processor according to claim 1, wherein said orthogonal transformation device performs discrete cosine transformation of the image data of a prescribed pixel matrix.
Claim 4
Dependent Claim
13 words
The data processor according to claim 1, wherein said coder performs Huffmann coding.