Transform Coding Example

The following experiment is intended to evaluate this transform for potential use in transform image coding. In this scenario, the transform coefficients of an image are quantized and then used to reconstruct an approximation to the original image. Different transforms will introduce different types of artifacts into the reconstruction.

The JPEG image compression standard is a transform coding technique which uses a block-based DCT. This experiment will apply the same coding technique (quantization of transform coefficients) to a facimile test image using the DGT and a block-based DCT. The DCT is implemented with 8x8 blocks to match the 8 pixel centers of the DGT basis functions.

An intelligent transform coding application employs a quantization scheme which exploits the properties of images and the transform. This scheme will differ depending on the actual transform used. In this experiment we will employ a uniform quantization scheme. While this would not be the technique of choice for a real implementation, it will serve to treat both the DGT and block-based DCT similarly and will demonstrate the character of the artifacts that are introduced. We have chosen uniform quantization of all coefficients to 5 bits.