New methods for the subsampling of color images are presented. A block-based orthogonalizing transform is used to represent the RGB image in an efficient domain. This transformation offers substantial advantages when preceded by a segmentation of the image based on chrominance content. An adaptive scheme, based on a threshold test on the local variance, is proposed for subsampling the resulting chrominance-related components. The proposed subsampling scheme outperforms conventional methods based on transforms such as the YCRCB, in terms of an improved quality versus sample-rate (or bit-rate) trade-off. It is possible to achieve 4:4:4 quality at near 4:2:0 rates. A block-based strategy to code the resulting color image components is also presented, which is based on the JPEG Baseline method.