Image Compression Apparatus and Image Compression Method

An image compression apparatus comprising:

• a dividing section for dividing an image to be compressed into blocks, each of which has a predetermined number of pixels having respective gradation value;
• a maximum value and minimum value search section for obtaining a maximum value and a minimum value of gradation values of the predetermined number of pixels in each block obtained by the dividing section;
• a discrimination section for determining whether each block of the divided blocks is a first kind block, in which an outline portion of the image is not included or a second kind block in which the outline portion of the image is included;
• and
• a normalization output section which divides a distribution range of gradation values, both ends of which correspond to the maximum value and the minimum value of each block of the divided blocks, in a case where a discrimination result of the discrimination section with respect to the block is the second kind block, into N areas (where N is an integer which is equal to 2 or greater) and outputs compressed data containing code data for showing to which area in the N areas, each pixel in each block belongs, and the maximum value and the minimum value, and which divides a distribution range of gradation values, both ends of which correspond to the maximum value and the minimum value of each block of the divided blocks, in a case where a discrimination result of the discrimination section with respect to the block is the first kind block, into M areas (where M is an integer which is greater than N) and outputs compressed data containing code data for showing to which area in the M areas, each pixel in each block belongs, the maximum value and the minimum value;
• wherein in a case of the first kind block, the normalization output section arranges the maximum value and the minimum value related to the block in a first order in a head portion of the compressed data, and in a case of the second kind block, the normalization output section arranges the maximum value and the minimum value related to the block in a second order that is a reverse order of the first order in a head portion of the compressed data.

An image compression method comprising:

• dividing an image to be compressed into blocks, each of which has a predetermined number of pixels having respective gradation value;
• obtaining a maximum value and a minimum value of gradation values of the predetermined number of pixels in each block obtained by the dividing section;
• determining whether each block of the divided blocks is a first kind block, in which an outline portion of the image is not included and a difference between the maximum value and the minimum value of the block is equal to or greater than a reference value or a second kind block other than the first kind block;
• dividing a distribution range of gradation values, both ends of which correspond to the maximum value and the minimum value of each block of the divided blocks, in a case where a discrimination result of the discrimination section with respect to the block is the second kind block, into N areas (where N is an integer which is equal to 2 or greater) and outputting compressed data containing code data for showing to which area in the N areas, each pixel in each block belongs, and the maximum value and the minimum value;
• dividing a distribution range of gradation values, both ends of which correspond to the maximum value and the minimum value of each block of the divided blocks, in a case where a discrimination result of the discrimination section with respect to the block is the first kind block, into M areas (where M is an integer which is greater than N) and outputting compressed data containing code data for showing to which area in the M areas, each pixel in each block belongs, the maximum value and the minimum value;
• and
• in a case of the first kind block, arranging the maximum value and the minimum value related to the block in a first order in a head portion of the compressed data, and in a case of the second kind block, arranging the maximum value and the minimum value related to the block in a second order that is a reverse order of the first order in a head portion of the compressed data.

An image compression method comprising:

• dividing an image to be compressed into blocks, each of which has a predetermined number of pixels having respective gradation value;
• obtaining a maximum value and a minimum value of gradation values of the predetermined number of pixels in each block obtained by the dividing section;
• determining whether each block of the divided blocks is a first kind block, in which an outline portion of the image is not included or a second kind block in which the outline portion of the image is included;
• dividing a distribution range of gradation values, both ends of which correspond to the maximum value and the minimum value of each block of the divided blocks, in a case where a discrimination result of the discrimination section with respect to the block is the second kind block, into N areas (where N is an integer which is equal to 2 or greater) and outputting compressed data containing code data for showing to which area in the N areas, each pixel in each block belongs, and the maximum value and the minimum value;
• dividing a distribution range of gradation values, both ends of which correspond to the maximum value and the minimum value of each block of the divided blocks, in a case where a discrimination result of the discrimination section with respect to the block is the first kind block, into M areas (where M is an integer which is greater than N) and outputting compressed data containing code data for showing to which area in the M areas, each pixel in each block belongs, the maximum value and the minimum value;
• and in a case of the first kind block, arranging the maximum value and the minimum value related to the block in a first order in a head portion of the compressed data, and in a case of the second kind block, arranging the maximum value and the minimum value related to the block in a second order that is a reverse order of the first order in a head portion of the compressed data.