Non-linear direct multi-scale image enhancement based on the luminance and contrast masking characteristics of the human visual system

Overcoming high luminance gradient using serial exposure time method for synchronous full-field measurement of temperature and deformation

The high-temperature optical method has been widely used for evaluating structural materials subjected to high temperature. Obtaining high-quality images of a specimen surface in such a harsh environment is detrimental for the accurate measurement of temperature and strain field. However, the high-temperature environment poses many challenges on these measurements, e.g., the large luminance gradient on the sample surface would jeopardize the image quality when using the full-field optical method. In order to overcome this issue, we propose here a simple and effective algorithm to obtain image sequences with serial exposure times. This algorithm incorporates exponentially decreasing exposure times to successfully reduce the disturbance caused by large luminance gradient, as will be shown by the verification on samples tested both in arc wind tunnel and oxy-propane torch flame. In comparison to the images with single exposure time, further experiment carried out on C/SiC sample up to 1100°C shows that image sequences with different exposure times can be effectively obtained by the image fusion technique. The calculation of the deformation and temperature fields using the image sequence method gives more accurate and reasonable results.

X-Ray Enhancement Based on Component Attenuation, Contrast Adjustment, and Image Fusion

Inspecting X-ray images is an essential aspect of medical diagnosis. However, due to an X-ray's low contrast and low dynamic range, important aspects such as organs, bones, and nodules become difficult to identify. Hence, contrast adjustment is critical, especially because of its ability to enhance the details in both bright and dark regions. For X-ray image enhancement, we therefore propose a new concept based on component attenuation. Notably, we assumed an X-ray image could be decomposed into tissue components and important details. Since tissues may not be the major primary focus of an X-ray, we proposed enhancing the visual contrast by adaptive tissue attenuation and dynamic range stretching. Via component decomposition and tissue attenuation, a parametric adjustment model was deduced to generate many enhanced images at once. Finally, an ensemble framework was proposed for fusing these enhanced images and producing a high-contrast output in both bright and dark regions. We have used measurement metrics to evaluate our system and achieved promising scores in each. An online testing system was also built for subjective evaluation. Moreover, we applied our system to an X-ray data set provided by the Japanese Society of Radiological Technology to help with nodule detection. The experimental results of which demonstrated the effectiveness of our method.

Power-constrained contrast enhancement algorithm using multiscale retinex for OLED display

This paper presents a power-constrained contrast enhancement algorithm for organic light-emitting diode display based on multiscale retinex (MSR). In general, MSR, which is the key component of the proposed algorithm, consists of power controllable log operation and subbandwise gain control. First, we decompose an input image to MSRs of different sub-bands, and compute a proper gain for each MSR. Second, we apply a coarse-to-fine power control mechanism, which recomputes the MSRs and gains. This step iterates until the target power saving is accurately accomplished. With video sequences, the contrast levels of adjacent images are determined consistently using temporal coherence in order to avoid flickering artifacts. Finally, we present several optimization skills for real-time processing. Experimental results show that the proposed algorithm provides better visual quality than previous methods, and a consistent power-saving ratio without flickering artifacts, even for video sequences.