A semi-adaptive DCT compression method that uses minimal space

Adaptive DCT (discrete cosine transform) compression methods outperform fixed DCT compression methods in terms of image quality, but they need a large amount of scratch space for the transformed image file. The author proposes a semi-adaptive DCT compression method that outperforms fixed DCT compression, but uses only a small amount of scratch space. This method was designed for use in an electronic still camera that is being developed by NASA. Simulation results show that at 2.25 bits per pixel, the SNR (signal to noise ratio) of the semi-adaptive method ranged from 35 dB to 42 dB as compared to a range of 34 dB to 42 dB for the fixed DCT method. At 3 bits per pixel, the semiadaptive method has an SNR that ranges from 40 dB to 47 dB