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Redmond, WA, United States

Rykowski R.,Radiant Imaging
Light and Engineering

Measured light source models have been widely used in ray trace simulations for optical design for more than 15 years now, but to date the generated ray sets have not contained spectral information. In some limited cases, tristimulus measurements can be helpful, but most ray tracing software requires a specific wavelength assigned to each ray to enable full colour simulations of an optical system. This paper describes and tests various techniques for combining spectral measurements with either photopic or tristimulus imaging colourimeters to produce ray sets that contain a wavelength. These ray sets can generally be readily used by most raytracing software to refract and diffract rays more accurately through the optical system and to generate illuminance or luminance distributions that also include colourimetric information. Finally, the methods are tested with real light sources where spectral power distribution varies significantly spatially across the light source and/or as a function of angle. Source

Crawled News Article
Site: www.extremetech.com

The original 2407WFP monitors had a problem with banding that turned out to be a firmware issue. If very specific patterns (such as DisplayMate’s test gradients) were sent to the monitor, the firmware could get confused and think it was a video feed and process the signal incorrectly, producing the color banding you see below: Our model is revision A02, and this newer firmware fixes that specific problem—mostly. There are three color-mode defaults in the monitor’s setup menu—Desktop, Multimedia, and Gaming. As long as you leave it in Desktop mode, the banding problem doesn’t pop up. In Multimedia or Gaming mode, it does. We’re not even sure what these modes do, besides tweak brightness and color values slightly. Just leave the monitor in Desktop mode, and you’re good to go. At default settings, the 2407WFP delivered about 300 cd/m2 of brightness, and full black was a reasonable .29 cd/m2, giving us an average contrast ratio of 1039:1—actually in line with the advertised spec. Turning the brightness down to about 100 cd/m2, more comfortable for viewing in a darkened room, the black levels didn’t decrease much, and the contrast ratio dropped to about 350:1. That’s still not bad for a display configured for viewing in a dark room, especially since this is a desktop PC monitor and is made to be used in somewhat more bright environments. Still, we would like to see the dark level pushed down to .20 cd/m2 or less. To the naked eye, backlight uniformity looks perfectly fine; color and brightness is uniform all over. Under closer examination with the Radiant Imaging device, we confirm what our eyes told us. At full white, the backlight is slightly biased toward the left side of the screen, but stays pretty consistent all over. At full black, we see one of the most uniform isoplots we’ve ever seen on a desktop LCD monitor. It’s a bit hotter in the upper right, but the differences are quite minor. In short, objective testing shows this to be one of the most uniform LCD desktop monitors we’ve seen. The PC Magazine response time, where a box is moved quickly around the screen at a regular speed (we tweak both box and background colors) showed minimal tearing and almost no ghosting. Our subjective tests during games backed it up: This monitor shows very little blurring or ghosting. Continued…

Crawled News Article
Site: www.extremetech.com

The VP2330wb comes out of the box with contrast set to 70% and brightness at 100%. The on-screen menu offers several color temperature settings as well as custom color adjustments, with the default at 6500K. This is where we took our initial tests. Note that the color temperature tracks way above 6500K across most brightness levels. It only approaches the 6500K level at 100% brightness. We were able to dramatically improve this curve with some color calibration, though. So if you pick up this monitor, you’ll want to color-calibrate it. The primary colors CIE chart doesn’t look half bad. It’s a little off from NTSC standard, but that’s not at all uncommon—nor necessarily a bad thing—for PC monitors. Moving on to the RGB levels histogram, we see that the red and blue values are totally off base through most brightness settings. Green tracks pretty well throughout, but the other two primary colors only get into the reasonable range up above 90% brightness. By delving into the custom color menus, we were able to make massive improvements in both the color temperature and RGB level tracking from dark to bright levels. After making these manual adjustments, the color accuracy of the monitor was really quite impressive. Continued…

Crawled News Article
Site: www.extremetech.com

The 2407WFP comes out of the box with the brightness setting set to 50%, and true to most Dell monitors, adjusting it all the way up or down the scale had a pretty minor effect. The brightness control doesn’t actually adjust the backlight, unfortunately, so the best way to tweak the monitor’s brightness is by using your video card control panel. Color temperature tracked just above 6500K through most of the brightness curve, bumping up a bit down around the 10% brightness level. These are quite good out-of-the-box results, and it didn’t take much tweaking to improve it further. Looking at the CIE chart, we can see the new 24″ Dell is a bit short on blue, but this is typical of LCD monitors. It’s actually tracking the primary colors quite accurately at full brightness. If we look at the color tracking for red, green, and blue individually across the brightness range, we see that the 2407 by default runs a bit green and goes way outside the range on blue in the very dark areas. Believe it or not, this isn’t bad color tracking for a display’s default settings. A little tweaking of the color controls in the on-screen menu let us clamp down those values and get quite uniform color everywhere above 30% brightness. Continued…

Fusco R.,Radiant Imaging | Sansone M.,University of Naples Federico II | Petrillo A.,Radiant Imaging
Applied Magnetic Resonance

The objective of this study was to evaluate the performances of different algorithms for diffusion parameters estimation in intravoxel incoherent motion method for diffusion-weighted magnetic resonance imaging (DW-MRI) data analysis. Traditionally, the method of non-linear least squares analysis by means of Levenberg–Marquardt algorithms has been used to estimate the parameters obtained from exponential decay data. In this study, we evaluated the Variable Projection curve-fitting algorithm and the performance of two non-linear regression methods when single and multiple starting points were used. Analysis was done on simulation data to which different amounts of Gaussian noise had been added. The performance of two non-linear regression methods was compared using the residual sum of squares and the number of failures in data fitting. We conclude that the VarPro algorithm is superior to the LM algorithm for curve fitting in intravoxel incoherent motion method for DW-MRI data analysis. © 2015, Springer-Verlag Wien. Source

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