An image pre-processing approach is proposed for joint source-channel coding (JSCC) scheme based on double protograph low-density parity-check (DP-LDPC) codes. Firstly, discrete cosine transform (DCT) and quantization are applied to the transmitted images. Different from the data processing of the previous approach for the quantized DCT coefficients, the representation of true form takes the place of complement form. Meanwhile, the high entropy frames will be pre-processed into low entropy frames through frame decomposition procedure due to the entropy of source frame limited by the code-rate of source code. Simulation results indicate that the JSCC scheme with the proposed image pre-processing approach improves the transmission efficiency and can recover the images with good quality at a very low signal-to-noise ratio (SNR).
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