Javier Bracamonte

Adaptive color image compression based on visual attention

This paper reports an adaptive still color image compression method which produces automatically selected ROI with a higher reconstruction quality with respect to the rest of the input image. The ROI are generated on-the fly with a purely data-driven technique based on visual attention. Inspired from biological vision, the multicue visual attention algorithm detects the most visually salient regions of an image. Thus, when operating in systems with low bit rate constraints, the adaptive coding scheme favors the allocation of a higher number of bits to those image regions that are more conspicuous to the human visual system. The compressed image files produced by this adaptive method are fully compatible with the JPEG standard, which favors their widespread utilization.

Efficient compressed domain target image search and retrieval

In this paper we introduce a low complexity and accurate technique for target image search and retrieval. This method, which operates directly in the compressed JPEG domain, addresses two of the CBIR challenges stated by The Benchathlon Network regarding the search of a specific image: finding out if an exact same image exists in a database, and identifying this occurrence even when the database image has been compressed with a different coding bit-rate. The proposed technique can be applied in feature-containing or featureless image collections, and thus it is also suitable to search for image copies that might exist on the Web for law enforcement of copyrighted material. The reported method exploits the fact that the phase of the Discrete Cosine Transform coefficients contains a significant amount of information of a transformed image. By processing only the phase part of these coefficients, a simple, fast, and accurate target image search and retrieval technique is achieved.

Adaptive block-size transform coding for image compression

In this paper we report the results of an adaptive block-size transform coding scheme that is based on the sequential JPEG algorithm. This minimum information-overhead method implies a transform coding technique with two different block sizes: N/spl times/N and 2N/spl times/2N pixels. The input image is divided into blocks of 2N/spl times/2N pixels and each of these blocks is classified according to its image activity. Depending on this classification, either four N-point or a single 2N-point 2-D DCT is applied on the block. The purpose of the algorithm is to take advantage of large uniform regions that can be coded as a single large unit instead of four small units-as it is made by a fixed block-size scheme. For the same reconstruction quality, the results of the adaptive algorithm show a significant improvement of the compression ratio with respect to the non-adaptive scheme.

VLSI systems for image compression: a power-consumption/image-resolution trade-off approach

Low power consumption is a requirement for any battery powered portable equipment. When designing ASICs for image and video compression, emphasis has been placed mainly on building circuits that are fast enough to satisfy the high data throughput associated with image and video processing. The imminent development of portable systems featuring full multimedia applications, adds the low-power constraint to the design of VLSI circuits for this kind of application. Several techniques such as lowering the supply voltage, architectural parallelization, pipelining etc., have been proposed in the literature to achieve low-power consumption. In this paper we report a VLSI circuit featuring a power management user-controllable technique that trades image quality for power consumption in a transform-based algorithm.

Bit-Rate Control for the JPEG Algorithm

JPEG is an international industry standard algorithm for compressing continuoustone still images. JPEG which stands for Joint Photographic Expert Group is currently one of the most popular encoding formats used for storing and transmitting images. JPEG is a variable coding bit-rate method and in this chapter two algorithms for controlling the produced compression ratio are reported. The bit-rate control techniques feature an excellent accuracy, a low computational complexity, and a full compliance with the JPEG standard bitstream. Furthermore, the application of these algorithms does not affect the quality of the decompressed images, i.e., to reach the target compression ratio there are no additional losses other than those inherent to JPEG. The most performant of the two bit-rate control techniques has been successfully implemented in a consumer electronics industrial prototype.

Smart low-power CMOS cameras for 3G mobile communicators

The paper presents the concept of a smart multifunctional low-power camera for 3G mobile communicators and Personal Digital Assistants. The device is composed of an ultra low-power image sensor featuring a large intra-scene dynamic range and a high sensitivity, so as to ensure proper image acquisition under possibly severe illumination conditions, as encountered in mobile. Further embedded functionalities encompass low-power still image compression, and low-power face authentication for secured access control.

Countering illumination variations in a video surveillance environment

In the field of video technology for surveillance applications it is often necessary to cope with the phenomenon of illumination variations. In fact, if not compensated, such variations can falsely trigger the change detection module that detects intrusions in video surveillance systems, thus affecting their reliability. Many studies have been made to solve the change detection problem under varying illumination conditions. Most of the published methods, however, rely only on the luminance information. The algorithm proposed in this paper exploits independently the information of each band of the RGB color space of the video sequences, thus producing a change detection algorithm that is more robust to illumination variations. These illumination variations are globally modeled by the so- called Von Kries model (also known as diagonal scaling model). This model is generally used to solve the color constancy problems, where conformance to a reference image illumination has to be guaranteed, like in color image retrieval applications. The use of this model is motivated by its low computational cost and by the interest of studying the relationship between color constancy and change detection. Based on practical experiments which confirm the interest in this method, new and more robust change detection algorithms are expected to be designed. In addition, the paper proposes the use of an iterative scheme whose aim is to improve the results obtained in the change detection module, and which is independent of this module, i.e., it can be used with other change detection schemes. It will be shown that the iteration can improve the quality of the final change mask, thus permitting to obtain a more effective change detection scheme.

Microcamera Embedded in a Wristwatch

The presentation reports upon the conception and realization of a miniature very low-power microcamera system that has been embedded in a wristwatch so as to enable the spontaneous capture of photographs in everyday life based on timekeeping devices the users would naturally wear. The designed microcamera system is fully operational and incorporates specific optics and a color VGA format based image sensor, a viewfinder enabling the selection of the scene to be captured, an image preprocessing step for color interpolation and white/color balance, followed by a dedicated JPEG compatible still image compression algorithm producing fixed-sized encoded images. Finally, the user is given the possibility to screen a posteriori (postview mode) the set of images captured, e.g. to erase less interesting ones in order to liberate the corresponding storage space. The user interface is composed of a particular display usually indicating the time, that is switching into a camera management mode for the acquisition and postview of photographs. Moreover, the camera can communicate with a personal computer through a cradle either to download the set of photographs acquired, or to upload a set of operational parameters, while simultaneously reloading the accumulator supplying the microcamera of the wristwatch. The technological challenge induced by the dense integration requirement of the numerous peripheral devices, including the central processing capabilities, the user and communication interfaces, and the tight power consumption constraints to be fulfilled, ask for the elaboration of numerous innovative solutions out of which only few were published so far. The purpose of the presentation is to provide insight into the system organization and its breakdown into original inter-playing hardware and software components, which were finally validated by the realization of an industrial prototype and demonstrator. The multi-fold experience collected by the partners in the design process is of course nurturing further activities, and, from a didactic viewpoint, offered the opportunity to set up practical laboratories that were dispensed in the realm of the Summer Schools Highlights in Microtechnology coordinated by the European Associated Laboratory (LEA) and more recently funded by the EU FP6 Marie Curie programme.

Design methodology for VLSI implementation of image and video coding algorithms—a case study

In this chapter a methodology for the design of VLSI circuits for image and video coding applications is presented. In each section a different phase of the design procedure is discussed, along with a description of the involved software environments. An example of an area efficient single-chip implementation of a JPEG coder is presented to illustrate the methodology.