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Part 1: Display Technology Shoot-Out

Comparing CRT, LCD, Plasma and DLP Displays By Dr. Raymond M. Soneira

Part I - The Primary Specs

Introduction
We are in a renaissance of display technologies. Ten years ago the CRT was the single prevalent technology. Today CRT, LCD, Plasma, DLP and LCoS are mature and mainstream technologies, with many more trying to emerge from the development lab and into significant market share. With all of these choices come the questions: how do they differ and which one should we get?

To provide some substantive answers we performed an in-depth comparison between these different display technologies in order to analyze the relative strengths and weaknesses of each. (Direct-view and rear-projection units were included but front projectors were excluded.) We used a combination of high-end laboratory instrumentation, advanced diagnostic test patterns, and old-fashioned viewing tests to compare them simultaneously in a side-by-side Shoot-Out. We chose the top performer for each technology using our own 2004 DisplayMate Best Video Hardware Guide. The candidates included a 40" direct-view LCD, the NEC LCD4000, a 61" Plasma, NEC 61XM2, a 50" DLP Rear Projection, Optoma RD-50, and a much smaller CRT 19" professional High Definition studio monitor, Sony PVM-20L5, which was used as the reference standard for color and gray-scale accuracy. There are many variations on LCoS, Liquid Crystal on Silicon, but only JVC's D-ILA technology can be classified as mature and mainstream. JVC recently announced rear-projection versions of its D-ILA (a 52" HD-52Z595 and a 61" HD-61Z595), which meet our selection criteria, but aren't included since they won't become available until the summer of 2004.

It's important to emphasize that this article is designed as a comparison of four different display technologies and not as an editorial review of the above models. By comparing the top performing model in each technology we are in effect examining the state-of-the-art for that technology. We will be looking at fundamental image and picture quality performance issues and not the implementation idiosyncrasies of any particular model.

Outline of the Article
The article is divided into three parts: in Part I we measure, analyze and compare primary specs like Black-Level, Color Temperature, Peak Brightness, Dynamic Range, and Contrast for each display. In Part II we'll continue with the Gray-Scale, Gamma, Primary Chromaticities and Color Gamut to see how they all affect color accuracy and introduce color hue and saturation errors. In Part III we'll study the complex world of display artifacts - just a fancy name for the image peculiarities - of each technology for both computer and television applications. We'll use diagnostic test patterns, images and a special selection of challenging DVD movies to stress and compare each technology.

  Instrumentation for Parts I and II
All of the test patterns were generated with DisplayMate for Windows Multimedia Edition -- on both DVI and component video. For HD signals we used an ATI Radeon 9800 Pro, with an ATI HDTV Component Video Adapter -- which provides high quality computer generated 720p and 1080i component video outputs YPBPR. We also used a pre-release version of the DisplayMate Professional DVD that has DisplayMate's proprietary test patterns on DVD (available later this year). All of the photometry and colorimetry measurements were made with a Konica Minolta CS-1000, which is a high-end laboratory Spectroradiometer with a narrow 1 acceptance angle for light emitted by the display. Most of the photometers and color analyzers that are used for display measurements are actually accurate only for CRTs because they rely on filters calibrated to the light spectrum of a CRT. They also have broad acceptance angles that are not accurate for many flat panel technologies because of their variation in light distribution with viewing angle. The Spectroradiometer measures the light spectrum directly and was crucial for making precise comparisons between the different display technologies. The Spectroradiometer and all of the displays (except for the Sony) were generously provided on a long-term loan basis by their manufacturers. We offer special thanks to all of them for agreeing to participate. It was especially challenging to get all of this high-end hardware together at the same time.


Black-Level
We start off the comparison with an item that doesn't get all of the attention it deserves: the display's ability to produce black. This capability of suppressing light output turns out to be a major challenge for all of the technologies. It's important because a poor black-level lifts the bottom end of the display's intensity-scale and introduces errors in both intensity and color throughout the entire lower end of the scale, not just at the very bottom. All displays produce some light in the form of a very dark-gray when asked to produce a black. This background light is added to all the colors and intensities that the display is asked to produce. This washes out the dark grays and also the dark colors. For example, dark reds will appear as shades of pink. What's more, if the display isn't properly adjusted, the dark background glow will have a color tint instead of a neutral gray, and this will add a color cast to the entire lower end of the intensity scale, which is particularly noticeable in dark images.

No display can produce a true black so it's important to know just how close it can actually get. CRTs do extremely well but the flat panels all struggle with black, yet they do pretty well with peak brightness, so the black-level can be a great differentiator. The actual black-level produced by a display is almost never reported in manufacturer's spec sheets or published reviews, yet for most applications it's actually more important than peak white brightness, which seems to get most of the attention. Black-level should be the single most important spec after screen size if you're working in multimedia, imaging, photography, home theater, or in any environment with controlled or subdued lighting.

All displays should have a black-level control to allow the black-level to be properly adjusted. The default factory value will almost certainly be inaccurate because the proper setting varies with the make and model of the graphics board, DVD player, or whatever signal source you're using. The black-level will also vary with the operating mode you select, such as the color-depth for a computer graphics board or progressive / interlaced scanning for a DVD player. The only way to properly adjust the black-level is with specialized test patterns, and we used the set in our own DisplayMate for Windows. One subtle point to bear in mind: in some cases it's necessary to intentionally misadjust the black-level control in order to compensate for some other display parameter or ambient lighting condition. We'll discuss this further in Parts II and III.

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Related Keywords:display technologies, CRT, LCD, Plasma, DLP, LCoS, shootout, diaplays, monitors


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