tranDCT is a tool for examining dependencies between DCT coefficients in an image. It should be useful not only for JPEG but basically for all DCT transformation based 2D compression schemes. tranDCT accepts input files of type PGM (Portable GrayMap), DCT (DCT coefficients with header), and TDS (TranDct Script) and writes PGM, DCT, RWC (RaW Coefficients), or CSV (Comma Separated Values) as output. By default it
converts PGM to DCT and vice versa. Be warned though, as this is not fully lossless due to roundoff errors in the IDCT/FDCT.

Download it from here:
tranDCT v0.9b (BSD)

Transformed DCT coeffients from a PGM file can be visualized in various formats. Please refer to the integrated help or to the included sample files for more information. If a TDS file and one or more PGM files are given as input, the output is an Excel/OpenOffice.Org compatible CSV file containing coefficient data for analysis. For the structure of a TDS file please refer to the included sample TDS file.

This is what the tranDCT sample output (one of it’s many options) typically looks like, created using the famous ‘Lena’ image (click to enlarge).

You may freely use tranDCT and it’s source code under the terms of the BSD. tranDCT is also included in my JPEG Open Source Developers Package.