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Dpcm ( Differential Pulse Code Modulation )


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in this presentation we tried to explain the DPCM technology

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Dpcm ( Differential Pulse Code Modulation )

  1. 1. What if we look at sample differences, not the samples themselves? dt = xt-xt-1 Differences tend to be smaller
  2. 2. First technique of image coding (~1952)
  3. 3. The pixel’s value can be predicted from its neighbors’s value. Sequences of pixels with similar value, will be found along a row of the image
  4. 4. To predict the value of a pixel from the previous values of the same row We predict that (for example) We make an error doing the prediction! If the actual value is (for example) the error is Information transmitted
  5. 5. Prediction If we know the past behavior of a signal up to a certain point in time, it is possible to make some inference about its future values Tapped-delay-line filter (discrete-time filter) A simple and yet effective approach to implement the prediction filter With the basic delay set equal to the sampling period
  6. 6. coder decoder
  7. 7. Same principle as 1-D • Definition of “Past” and “Future” in images: Predictions: – horizontal (scan line) – vertical (column) – 2-dimensional
  8. 8. Prediction example: cameraman
  9. 9. Adaptive Differential Pulse Code Modulation (ADPCM) Why we talk about ADPCM when we talk about DPCM ?? *Adaptive similar to DPCM, but vary the mapping of bits to difference dynamically. $ If rapid change, use large differences $ If slow change, use small differences
  10. 10. CS 414 - Spring 2012 Adaptive Differential Pulse Code Modulation (ADPCM) Fig : show the ADPCM
  11. 11. Conclusion: • DPCM can efficiently remove this redundancy. • Only the differences between samples are sent. • Normally the difference is small . • The technology in which vary the mapping of bits to difference dynamically is ADPCM .