ations. Scalar and Vector represent the two major types of quantizers. These can be further classified as memoryless or containing memory, and symmetric or nonsymmetric. F (u, v) = Scalar quantizers control the values taken by a single variable. The quantizer defined by the MPEG-1 encoder scales the DCT transform coefficients. Vector quantizers operate on multiple variables, i.e., a vector of variables, and become very complex as the number of variables increases. This discussion will introduce the reader to the (b) DCT Coefficients basic scalar and vector quantizer concepts that are rele- vant to image and video encoding. Figure 7.4-5 8x8 discrete cosine transform. CHAPTER 7.4 Video compression errors are uniformly distributed. The quantizers specified [13] and tree search VQ (TSVQ) [14]. The LBG design in the H.261, H.263, MPEG-1, and MPEG-2 video is based on the Lloyd-Max scalar quantizer algorithm. It coders are nearly uniform. They have constant step sizes is widely used because the system parameters can be except for the larger dead zone area (the input range for generated via the use of an input "training set" instead of which the output is zero). the true source statistics. The TSVQ design reduces VQ Non-uniform quantization is typically used for codebook search time by using m-ary tree structures and non-uniform input distributions, such as natural image searching techniques. sources. The scalar quantizer that produces the mini- mum MSE for a non-uniform input distribution will have non-uniform steps. As compared to the uniform quan- 7.4.5.4 Motion compensation and tizer, the non-uniform quantizer has increasingly better estimation MSE performance as the number of quantization steps increases. The Lloyd-Max [12] is a scalar quantizer Motion compensation [15] is a technique created in the design that utilizes the input distribution to minimize the 1960s which is used to increase the efficiency of video MSE for a given number of output levels. The Lloyd-Max encoders. Motion compensated video encoders are p