Progressive image transmission

Progressive image transmission involves approximate reconstruction of an image whose fidelity is built up gradually until the viewer decides either to abort transmission or allow further reconstruction. Eventually an exact replica of the original image may be reconstructed. Researchers have proposed a variety of techniques to achieve progressive image transmission. The international body specifying standards for still image compression is the JPEG (Joint Photographic Experts Group). The JPEG has specified standards for progressive as well as hierarchical image coding using DCT. The alternatives appearing in this standard are spectral selection and successive approximation of DCT coefficients and hierarchical pyramidal encoding. The authors study the performance of three progressive image transmission schemes. The performance has been compared using bit-rate (bits/pixel) for given image size, normalised SNR and/or subjective quality evaluations