Patent ID: 8023749

Claim:
An image compressing apparatus that compresses input document image data by JPEG compression comprising: document type discrimination means for calculating with a following equation 1 a document discrimination signal indicating a proportion that a text area accounts for in one page of a document for the document image data; document discrimination signal=(text pixel count value÷total number of pixels)×100 (Equation 1), where total number of pixels=text pixel count value+halftone dot pixel count value+other pixel count value; and parameter setting means for setting parameters for JPEG compression in accordance with the document discrimination signal, where the parameter setting means for setting parameters for JPEG compression performs said setting by calculating with a following equation 2 parameters for setting values of AC components in a quantization table for JPEG compression at least based on the document discrimination signal; AC component ( i,j )=default value ( i,j )×(document discrimination signal ×(α+β)) (Equation 2), where (i,j) are coordinates indicating a position in the quantization table, the default value is an arbitrary quantization table, and α and β are arbitrary real numbers and α<0, β>0; and JPEG compression means for setting parameters calculated by the parameter setting means to execute a JPEG compression process.