【作者】 李晓明；

【导师】 严晓浪； 沈海斌；

【作者基本信息】 浙江大学 ， 电路与系统， 2005， 硕士

【摘要】 论文包括两方面:离散余弦变换和反变换(DCT/IDCT)及图像后处理算法(Deblocking)的实现。离散余弦变换是广泛应用于信号处理、图像处理邻域的重要工具之一,已经被多个国际标准所接受,如JPEG、MPEG、H.263等。DCT应用到实际系统中的前提是具有能够快速实现的算法,自从1977年第一个真正的DCT快速算法出现以来,寻求更快、更规则、更简单的DCT算法一直是信号处理邻域的一个研究方向。本文提出了一种高效的二维余弦变换和反变换(DCT/IDCT)硬件设计算法。采用行列分解技术,我们通过正确的安排输入序列,通过子表达式共享技术优化乘法操作,并使用进位保留加法器(CSA)实现乘法操作,把二维DCT/IDCT公式化为一个循环卷积过程来进行DCT/IDCT计算。使用循环卷积方法在计算得到不同的DCT/IDCT输出过程中有利于挖掘字级的数据共享,而使用公共子表达式共享技术则有利于比特级的数据共享。与其他现有的设计相比较,本设计在算法和硬件实现上都有突出表现。Deblocking是一种图像的后处理算法,主要用于去除编码效应以提高图像的视觉效果,这些算法通常是一些计算密集型的,通常需要高速处理器来实现实时操作。本文根据MPEG-4标准提出了一种Deblocking滤波器算法的结构。该结构有两个不同的滤波模式,并通过块缘象素信息来选择采用何种模式。在每一个模式下,分别对水平和竖直边沿进行一维滤波操作。根据人类视觉系统(HVS),人眼对平滑部分的变化更敏感,而由运动补偿技术从前一帧引入的块状效应同样分布于块的内部,因而在第一种滤波方式下,对应于一个平滑区域,采用一个强的滤波器应用于块的边沿并延伸至块内。而第二种则根据边沿象素信息采用一个经验式的滤波方式,以自适应地去除边缘效应而不使图像模糊。尽管该设计相对简单,但它无论从主观上还是客观上提高了图像质量。更多还原

【Abstract】 The thesis includes two parts: the research for implementation structure of efficient two-dimensional (2-D) discrete cosine transform and inverse discrete cosine transform (DCT/IDCT) and image post-processing (Deblocking).The discrete cosine transform is one of the important tools in signal processing and image/video processing, which is accepted by several international standards, such as JPEG, MPEG, H.263. The precondition for using DCT in practical system is the algorithms for fast implementation of DCT existing. Since the first true DCT fast algorithm for DCT is proposed in 1977, looking for the faster, more structured and simpler algorithm for DCT is one of research topics in signal processing fields. This thesis proposes an efficient two-dimensional 2-D DCT/IDCT design. Adopting the row-column decomposition technique for computing 2-D DCT/IDCT, we formulate the one-dimensional (1-D) DCT/IDCT into cyclic convolution by properly arranging the input sequence, optimize the multiplications based on the concept of common subexpression sharing, and carry out the multiplications through carry-save adder (CSAs). Using cyclic convolution is helpful in exploiting the word-level data sharing in computing different DCT/IDCT outputs. Adopting the common subexpression sharing is beneficial to the bit-level data sharing in computing the outputs. Compared with some existing DCT/IDCT designs, the proposed design is distinguished in algorithm and implementation.Deblocking is a kind of image post-processing technique largely used to remove coding artifacts and improve the visual quality. The algorithm used to achieve these tasks is computationally intensive and usually require high speed processors to be able to run in real time. The thesis presents a deblocking filter architecture recommended by MPEG-4 standard. This architecture supports two separate filtering modes, which are selected by pixel behavior around the block boundary. In each mode, proper one-dimensional filtering operations are performed across the block boundary along the horizontal and vertical directions, respectively. In the first mode, corresponding to flat region, a strong filter is applied inside the block as well as on the block boundary because the flat regions are more sensitive to the human visual system (HVS) and the artifacts propagated from the previous frame due to motion compensation are distributed inside the block. In the second mode, corresponding to other regions, a sophisticated smoothing filter, which is based on the frequency information around block boundaries, is used to reduce blocking artifacts adaptivelywithout introducing undesired blur. Even though the proposed deblocking filter is quite simple, it improves both subjective and objective image quality for various image features.更多还原