While watermarking algorithms have been developed for many types of digital content, little work has been done to develop watermarking algorithms for the class of map and chart images, despite their relative value. These images are generally of high resolution, have large areas of homogeneous pixels and are color-mapped or binary. These characteristics impede the use of watermarking algorithms designed for continuous-tone photographic images. This paper presents a novel blind watermarking algorithm designed for map and chart images. The algorithm segments the image into homogeneous regions and adds multiple watermark signals to the locations of the pixels on the boundary of several regions. The presence of these signals in the watermarked image is determined using a correlation-based detector. The watermarks can be detected in the presence of synchronization errors such as those incurred by cropping the image, or shifting by several columns or rows, and in the presence of noise. The algorithm is designed to efficiently process typical map images, which can have resolutions on the order of several 100 million pixels.
This paper presents a Rate-Distortion based optimization procedure for video coding that explicitly incorporates a perceptual distortion measure. A flexible MINMAX (minimizing the maximum distortion) optimization procedure based on Linear Programming (LP) is used to minimize the variation in distortion across frames. The distortion measure utilizes a multi-channel human vision model to generate a map of the perceived distortion at each pixel in a frame. This map is then collapsed into a single frame-level distortion. Lagrangian optimization is employed within each frame to assign macroblock-level quantization step-sizes that minimize this frame-level distortion. Coding results with MPEG-2 show a large reduction in peak perceived distortion with respect to TM5 as well as lower variation in distortion across the frames in the video sequence. Although results are presented for a specific metric, the LP based optimization procedure easily extends to other distortion measures.
Many current quality evaluation models were designed to produce a single estimate of perceived quality for a video sequence coded at relatively high rates. These metrics perform a multi-channel decomposition to simulate the processes of the Human Visual System (HVS), followed by a distortion pooling stage that collapses the channels over frequency, time and space. Estimating quality at short intervals over the length of a video sequence, however, may be more useful for long video sequences than a single estimate, particularly in such applications as two pass video coding and video quality monitoring. This paper presents an objective metric designed to perform this task on video sequences coded at low bit rates. The metric implements a wavelet transform-based model of the human visual system and a method of temporal error pooling suited to continuous estimation of perceived quality. A time series distance metric based on piecewise linear representations is also introduced in order to quantify performance. The metric is evaluated on a wide range of low bit rate video content and shown to perform well in terms of the shape and overall mean of the output perceived quality waveform.
A subjective quality evaluation was performed to qualify vie4wre responses to visual defects that appear in low bit rate video at full and reduced frame rates. The stimuli were eight sequences compressed by three motion compensated encoders - Sorenson Video, H.263+ and a Wavelet based coder - operating at five bit/frame rate combinations. The stimulus sequences exhibited obvious coding artifacts whose nature differed across the three coders. The subjective evaluation was performed using the Single Stimulus Continuos Quality Evaluation method of UTI-R Rec. BT.500-8. Viewers watched concatenated coded test sequences and continuously registered the perceived quality using a slider device. Data form 19 viewers was colleted. An analysis of their responses to the presence of various artifacts across the range of possible coding conditions and content is presented. The effects of blockiness and blurriness on perceived quality are examined. The effects of changes in frame rate on perceived quality are found to be related to the nature of the motion in the sequence.