Quantization (image processing)

About: Quantization (image processing) is a research topic. Over the lifetime, 7977 publications have been published within this topic receiving 126632 citations.

Reverse engineering of double JPEG compression in the presence of image resizing

Abstract: In this paper, we propose a forensic technique for the reverse engineering of double JPEG compression in the presence of image resizing between the two compressions Our approach is based on the fact that previously JPEG compressed images tend to have a near lattice distribution property (NLDP), and that this property is usually maintained after a simple image processing step and subsequent recompression The proposed approach represents an improvement with respect to existing techniques analyzing double JPEG compression Moreover, compared to forensic techniques aiming at the detection of resampling in JPEG images, the proposed approach moves a step further, since it also provides an estimation of both the resize factor and the quality factor of the previous JPEG compression Such additional information can be used to reconstruct the history of an image and perform more detailed forensic analyses

ASIC and FPGA implementations of H.264 DCT and quantization blocks

Abstract: In the search for ever better and faster video compression standards H.264 was created. With it arose the need for hardware acceleration of its very computationally intensive parts. To address this need, this paper proposes two sets of architectures for the integer discrete transform (DCT) and quantization blocks from H.264. The first set of architectures for the DCT and quantization were optimized for area, which resulted in transform and quantizer blocks that occupy 294 and 1749 gates respectively. The second set of speed optimized designs has a throughput anywhere from 11 to 2552 M pixels/s. All of the designs were synthesized for Xilinx Virtex 2-Pro and 0.18/spl mu/m TSMC CMOS technology, as well as the combined DCT and quantization blocks went through comprehensive place and route flow.

Method and apparatus for coding and decoding digital image data using image quantization modification

Abstract: An image coding method and apparatus for transforming and quantizing an image to produce transformed and quantized coefficients. The coefficients are coded and a complexity index value is obtained from the input image to calculate local characteristic values used to modify the quantization scale. In this manner, rate control is obtained on the basis of the local characteristics of the image, whereby the quality of the coded image and the precision of the rate control is improved.

Image sensor and electronic still camera with an addressable image pickup section and an analog product sum calculation section

Abstract: An electronic still camera wherein an image compression circuit can be simplified includes a lens system, a shutter, an image sensor and a processing circuit. A video signal for one frame outputted from the processing circuit in response to a shutter operation is written into a memory. A video signal read out from the memory is compressed in accordance with the JPEG system by an image compression circuit and then written into a memory card. The image sensor is constituted from an image pickup section and a product sum calculation section. A CMD image sensor capable of non-destructively reading out a picture signal is used as the image pickup section. The product sum calculation section performs DCT processing required for compression processing of the JPEG system. Since a detected image signal processed by DCT processing is obtained from the image sensor, DCT processing of the image compression circuit is unnecessary.

The cost of JPEG compression anti-forensics

Abstract: The statistical footprint left by JPEG compression can be a valuable source of information for the forensic analyst. Recently, it has been shown that a suitable anti-forensic method can be used to destroy these traces, by properly adding a noise-like signal to the quantized DCT coefficients. In this paper we analyze the cost of this technique in terms of introduced distortion and loss of image quality. We characterize the dependency of the distortion on the image statistics in the DCT domain and on the quantization step used in JPEG compression. We also evaluate the loss of quality as measured by means of a perceptual metric, showing that a perceptually-optimized version of the anti-forensic method fails to completely conceal the forgery. Our conclusion is that removing the traces of the JPEG compression history could be much more challenging than it might appear, as anti-forensic methods are bound to leave characteristic traces.