THESIS PROPOSAL - Pooja Vasant Agawane Student I.D.: 1000-522-697 Date : August 20, 2007IMPLEMENTATION AND EVALUVATION OF THE RESIDUAL COLOR TRANSFORMOBJECTIVE:The objective of the thesis is to implement and evaluate the performance of Residual ColorTransform (RCT) [9] applied to the High Definition test sequence [16]. This thesis aims tocompare the performance of the RCT with the lossless coding tools in the JM referencesoftware [16].MOTIVATION:The 4:4:4 video sampling format is gaining a lot of attention due to its significance in theprofessional applications. Both the industry and the academia are actively involved toachieve better compression efficiency and high coding gain in RGB (red, green, and blue)color space. In contrast to typical consumer applications, the high quality of the video isdemanded in the applications such as professional digital video recording or digital cinema /large-screen digital imagery. These applications require all three color components to berepresented with identical spatial resolution. Moreover, for this kind of applications, samplevalues in each color component of a video signal are expected to be captured and displayedwith a precision of more than 8 bits. These specific characteristics are posing new questionsand new challenges, especially regarding the choice of an optimal color space representation.Typically, both for video capture and display purposes the RGB color space representationcan be considered as the natural choice. From a coding point of view, however, the RGBdomain is often not the optimum color space representation, mainly because for naturalsource material usually significant amount of statistical dependencies among the RGBcomponents can be observed. Thus, in order to take advantage of these statistical properties,the usage of a decorrelating transformation from the original RGB domain to someappropriate color space is often recommended. [2]DISADVANTAGES OF YCbCr AND INTRODUCTION OF YCgCo COLOR SPACE:Typically, a video is captured and displayed using the RGB (Red, Green and Blue) colorspace. The disadvantages of encoding the video in RGB domain are:- Color components in the RGB domain are highly correlated.- The response of the human visual system (HVS) is better matched to the luminanceand chrominance components, rather than RGB. The HVS is very sensitive to theluminance information in the image. It is less sensitive to the chrominancecomponents.The YUV color space represents this luminance and chrominance information in a givenRGB image. Hence the color conversion from the RGB domain to the YUV domain forencoding is performed. This conversion can be performed as follows [20]:Y = 0.299R + 0.587G + 0.114B U = − 0.147R − 0.289G + 0.436B V = 0.615R − 0.515G − 0.100BIn the YUV domain, the chrominance samples can be subsampled. This leads to compression.Then the inverse transform is performed from the YUV to RGB for display.YCbCr is a family of color spaces. Y stands for Luminance, Cb represents the blue chromnaand Cr represents the red chroma. The conversion from RGB to YCbCr can be performed asfollows [7]:with, e.g., KR = 0.2126, KB = 0.0722.There are two problems with this approach:- The samples are actually represented using integers. The rounding error is introducedin both the forward and inverse color transformations. - The above transformation was not originally designed for digital video compression.It uses a sub-optimal trade-off between the complexity of the transformation (withdifficult-to-implement coefficient values such as 0.2126 and 0.0722) and codingefficiency. Considering the second problem, a new color space called YCgCo (where the "Cg" stands forgreen chroma and the "Co" stands for orange chroma) has been introduced. This is muchsimpler and typically has equal or better coding efficiency. The conversion from the RGB tothe YCgCo color space can be performed as follows [7]:.This conversion reduces the complexity of conversion from the RGB domain to YCbCr andalso increases the coding efficiency.RESIDUAL COLOR TRANSFORM:The residual color transform maps RGB to the YCoCg color space. The characteristics of theYCgCo color space can be explained as follows [8]: - This color transform has been shown to be capable of achieving a decorrelation thatis much better than that obtained by various RGB-to-YCbCr transforms and which, infact, is very close to that of the Karhunen-Loeve transform [23].- The transform is reversible in the sense that each original RGB triple can be exactlyrecovered from the corresponding YCoCg triple if the color difference componentsCo and Cg are represented with one additional bit accuracy relative to the bit depthused for representing RGB, and if furthermore, no information loss in any subsequentcoding step is assumed. - Both the forward and inverse RGB-to-YCoCg transforms require only a few shift andadd operations per triple which, in addition, can be performed inline, i.e., without theneed of some extra memory apart from one single auxiliary register:The “>>”-operator denotes the bitwise right shift operator. OVERVIEW OF H.264:H.264/MPEG-4 AVC is the latest video coding standard. It is noted for achieving very highdata compression. H.264 is aimed at achieving high quality video at low bit rates ascompared to previous standards of MPEG-2, H.263 and MPEG-4 part 2. The price to be paidis an increase in complexity where the decoder complexity is about four times that of MPEG-2 and two times that of MPEG-4 Part 2 Visual [6]. The basic coding structure of H.264 is similar to the previous standards of MPEG-1,MPEG-2, H.263, etc. [3]. This coding structure is referred to as motion compensated –transform coding structure. A video is a group of pictures and it is coded by considering onepicture at a time. A picture is considered as a group of slices. A picture can have one or moreslices. A slice consists of a sequence of macroblocks (MB). Each MB is 16*16 pixels ofluminance component (Y) and 8*8 pixels of two chrominance components (Cb and Cr) forthe 4:2:0 sampling format. This 16*16 luminance macroblock can be partitioned into subblocks of 16*8, 8*16 and 8*8. Each 8*8 luminance can be further partitioned in 8*4, 4*8 and4*4 sub blocks. The hierarchy of video
View Full Document
Unlocking...