A common task of tone mapping algorithms is to reproduce high dynamic range images (HDR) on low dynamic range (LDR) display devices such as printers and monitors. We present a new tone mapping algorithm for the display of HDR images that was inspired by the adaptive process of the human visual system. The proposed algorithm is based on center/surround Retinex processing. Our method has two novel aspects. The input luminance image is first compressed by a global tone mapping curve. The curvature of the compression curve is adapted locally based on the pseudo-Hilbert scan technique, so it can provide a better overall impression before the subsequent local processing. Second, the local details are enhanced according to a non-linear adaptive spatial filter (Gaussian filter), whose shape (filter variance) is adapted to the high-contrast edges of the image. The proposed method takes advantage of the properties of both global and local processing while overcoming their respective disadvantages. Therefore, the algorithm can preserve visibility and contrast impression of high dynamic range scenes in standard display devices. We tested the proposed method on a variety of HDR images and also compared it to previous research. The results indicated that our method was effective for displaying images with high visual quality.
We propose here a video server system that streams transmissions of consumer generated video (CGV) files. The CGV files are placed in Internet small computer system interface (iSCSI, i.e., SCSI over TCP/IP) storage devices at each individual's home, and these storage devices are connected to one video server on demand. Because iSCSI uses the TCP protocol, the network delay greatly affects the iSCSI throughput. Although iSCSI storage devices have different network delays for video servers, it is important to design the system so that the streaming transmission quality does not depend on network delays. To ensure the scalability of streaming transmissions, we use a technique to dynamically control the number of TCP connections in the iSCSI protocol. Simulation results showed that the CGV file streaming transmission quality at 3 Mbit/s was stable when the round-trip times between the servers and the storage devices were less than 100 ms.
To assist radiologists in interpreting diffusion-weighted magnetic resonance images (DWI), we have developed a computerized scheme for proper adjustment of these images that is based on density histogram analysis of concurrent images (b0 images). In our computerized scheme, the gray level of a b0 image is first normalized and the brain region is segmented using thresholding and labeling techniques. The density histogram is then calculated from the brain region on the original b0 image and the pixel value of maximum frequency in the density histogram is determined. The display grayscale in the DWI is finally adjusted by using the determined pixel value. With the existing adjustment method using thalamic signal intensity, the variation between 60 cases of evaluation index for image contrast calculated from the adjusted DWI was ±24.2% and with our method, it was ±16.5%. Our computerized scheme is therefore a very promising technique for determining the display grayscale of brain DWI.
The preferred luminance level of LCD televisions under real viewing conditions to obtain both good picture quality and low power consumption is a rather controversial issue. The relationship between the preferable luminance and major parameters that affect it were investigated in a field test and laboratory experiments. In the field test of 83 households, the illuminance and luminance of television screens and television viewing distances were measured on site. The results indicated that the mean display luminance was 269 cd/m2 for LCD televisions. The median screen illuminance was 92 lx and the median viewing distance was 252 cm. In laboratory experiments, younger and older subjects adjusted the luminance of an LCD television screen to their preferred levels under different screen illuminance levels, angular screen sizes and average luminance levels (ALL) of images. Based on the results, the preferred luminance of LCD television screens for younger and older subjects is represented as two formulas. When the ALL of images was 25% and the screen illuminance and angular screen size were set at 100 lx and 20°, respectively, the preferred luminance was 160 cd/m2 for younger subjects and 248 cd/m2 for older subjects. By setting the preferred luminance of an LCD television under real viewing conditions, it is possible to not only reduce visual fatigue but also to conserve energy consumption.
A super-resolution method using the bilateral filter has recently been proposed. In this letter, we improve its image reconstruction capability by extending the bilateral filter used in that method to the spatially anisotropic filter and show with experiments that the reconstruction error in the proposed method is lower than the previous method using the isotropic bilateral filter.