We consider the perceptual quality optimization in image coding through adaptive quantization. A differential contrast model is proposed to measure the visual sensitivity to the quantization distortions, and thereby deriving the spatially adaptive quantization strategy. A complementary quantitative approach is provided as a means to efficiently calculate the proposed differential contrast model. The resulting visual quality improvement is experimentally demonstrated.

A rapidly increasing portion of internet traffic is dominated by requests from mobile devices with limited and metered bandwidth constraints. To satisfy these requests, it has become standard practice for websites to transmit small and extremely compressed image previews as part of the initial page load process to improve responsiveness. Increasing thumbnail compression beyond the capabilities of existing codecs is therefore an active research direction. In this work, we concentrate on extreme compression rates, where the size of the image is typically 200 bytes or less. First, we propose a novel approach for image compression that, unlike commonly used methods, does not rely on block-based statistics. We use an approach based on an adaptive triangulation of the target image, devoting more triangles to high entropy regions of the image. Second, we present a novel algorithm for encoding the triangles. The results show favorable statistics, in terms of PSNR and SSIM, over both the JPEG and the WebP standards.

A method and apparatus for performing sparse coding dictionary priming are disclosed. Sparse coding dictionary priming may include iteratively training a coding dictionary, which may include a plurality of codewords or bases. Iteratively training the coding dictionary may include identifying a sampling index cardinality, identifying a portion of a video stream, decomposing the portion of the video stream, and updating the codeword based on the portion of the video stream. Decomposing the portion of the video stream may include randomly identifying a set of codewords from the plurality of codewords wherein a cardinality of the set of codewords is the sampling index cardinality and wherein the sampling index cardinality is less a cardinality of the plurality of codewords, and determining a codeword having a maximum correlation with the portion of the video stream from the set of codewords.