1. An imaging apparatus for taking an image by making use of a solid-state imaging sensor, said imaging apparatus comprising: a compression section configured to compress image data, which is generated by said solid-state imaging sensor as a result of an imaging process, by dividing said image data into blocks each composed of a fixed number of same color component pixels adjacent to each other and taking each of said blocks as a unit of compression: a memory used for temporarily storing compressed image data produced by said compression section; a decompression section configured to decompress said compressed image data read out from said memory; and a signal processing section configured to carry out an image-quality correction process on decompressed image data produced by said decompression section, wherein each of said blocks is split in advance into two quantization-subject areas each composed of one or more pixels adjacent to each other, a plurality of block types are defined in advance for each of said blocks, said block types defined for any individual one of said blocks are distinguished from each other by the position of the inter-area boundary between said two quantization-subject areas in said individual block, and said compression section has a dynamic-range computation sub-section configured to compute a dynamic range of pixel data, of pixels in each of said quantization-subject areas for each of said quantization-subject areas in each of said blocks, a block-type select sub-section configured to compute a sum of said dynamic ranges, which are each computed by said dynamic-range computation sub-section for one of said quantization-subject areas in any individual one of said blocks, for each of said block types defined for said individual block on the assumption that each of said block types has been selected for said individual block and select said block type having a smallest sum of said dynamic ranges among all said block types defined for said individual block as a proper block type for said individual block, and a quantization processing sub-section configured to quantize a difference, which is obtained as a result of subtracting the smallest pixel data among all pixels in any individual one of said quantization-subject areas from the pixel data, of each of said pixels in said individual quantization-subject area, in accordance with said dynamic range, which is computed by said dynamic-range computation sub-section for said individual quantization-subject area, for every pixel in said quantization-subject areas which are included in any individual one of said blocks as quantization-subject areas having an inter-area boundary conforming to said proper block type selected by said block-type select sub-section for said individual block.