tailieunhanh - Image and Videl Comoression P3

Instead of encoding a signal directly, the differential coding technique codes the difference between the signal itself and its prediction. Therefore it is also known as predictive coding. By utilizing spatial and/or temporal interpixel correlation, differential coding is an efficient and yet computationally simple coding technique. In this chapter, we first describe the differential technique in general. Two components of differential coding, prediction and quantization, are discussed. There is an emphasis on (optimum) prediction, since quantization was discussed in Chapter 2. When the difference signal (also known as prediction error) is quantized, the differential coding is called differential pulse code. | 3 Differential Coding Instead of encoding a signal directly the differential coding technique codes the difference between the signal itself and its prediction. Therefore it is also known as predictive coding. By utilizing spatial and or temporal interpixel correlation differential coding is an efficient and yet computationally simple coding technique. In this chapter we first describe the differential technique in general. Two components of differential coding prediction and quantization are discussed. There is an emphasis on optimum prediction since quantization was discussed in Chapter 2. When the difference signal also known as prediction error is quantized the differential coding is called differential pulse code modulation DPCM . Some issues in DPCM are discussed after which delta modulation DM as a special case of DPCM is covered. The idea of differential coding involving image sequences is briefly discussed in this chapter. More detailed coverage is presented in Sections III and IV starting from Chapter 10. If quantization is not included the differential coding is referred to as information-preserving differential coding. This is discussed at the end of the chapter. INTRODUCTION TO DPCM As depicted in Figure a source encoder consists of the following three components transformation quantization and codeword assignment. The transformation converts input into a format for quantization followed by codeword assignment. In other words the component of transformation decides which format of input is to be encoded. As mentioned in the previous chapter input itself is not necessarily the most suitable format for encoding. Consider the case of monochrome image encoding. The input is usually a 2-D array of gray level values of an image obtained via PCM coding. The concept of spatial redundancy discussed in Section tells us that neighboring pixels of an image are usually highly correlated. Therefore it is more efficient to encode the gray difference .