Posted Fri Feb 25, 2011 at 10:40 AM PST by Joshua Zyber
Editor's Note: Each Friday, High-Def Digest's own HD Advisor will answer a new round of questions from our readers. If you have home theater questions you need answered, send an email to [email protected]
Answers by Joshua Zyber
Contrast on Digital Displays
Q: What is your experience with films/scenes that are dimly lit, or have low contrast? I have found on several LCD TVs that this is a weak point. Pictures look stunning on well-lit blockbusters, but fail on the artier more natural lighting and low contrast. The night shots of 'Braveheart' look awful despite its sterling reviews. People's facial features trail the blacks. It would seem the gray to gray response is a little slow. My current set is a Sony 32EX503. It also received excellent reviews, but it fails in these areas. Have you found this to be a common problem with LCDs? Or is it an issue with certain brands? I would really appreciate some advice from the high def-experts.
A: Contrast is a very common failing of digital display technologies, especially LCD. As you note, many LCD televisions look stunning in brightly-lit scenes, but turn into a murky mess in dark scenes. The black levels aren't particularly dark, and shadow detail is frequently crushed. Plasma and LCoS (Liquid Crystal on Silicon) are traditionally stronger in this area, but ironically still lag in contrast reproduction behind the old CRT technology that is virtually extinct in the modern market. (I must note, however, the most digital displays exceed CRT quality in many other respects.)
In an attempt to improve the perception of contrast, many LCD televisions implement dynamic contrast adjustment features. The most common application of this is to add an automated iris in front of the lamp that will cut the brightness of light output during predominantly dark scenes. Less light equals a darker picture. While this helps to improve black levels, it does so at the expense of brighter portions of the image. For example, if a scene takes place in a dark room with one bright light in the far corner, a dynamic iris will close down to darken the picture, and thus will dim that bright light.
In a worst case scenario, movie scenes that alternate or transition from dark to bright may exhibit a "pumping" of black levels as the dynamic iris struggles to find the right setting. I see this all the time on my living room television whenever a movie's end credits (small white text on a black background) come up. The iris immediately clamps down because it detects a predominantly dark picture, but then opens up again as more white text fills the frame. I also like to use the opening scene in the first 'Star Wars' movie as a torture test for a dynamic iris. The scene opens with a dark star field, and then brightens considerably as the Imperial Destroyer ship flies overhead and occupies more and more of the frame. As this happens, you can watch the darkness of space in the background turn into a milky shade of gray.
Some (but not all) LCD televisions offer the ability to adjust the intensity of the dynamic iris or turn it off completely. The weaker setting (or off position) will reduce pumping artifacts, but at the expense of black levels. This is a trade-off you will have to judge for yourself based on the performance of each specific TV model.
A better option than a dynamic iris is an LCD set illuminated by a full LED backlight with local dimming. In this type of television, the picture is divided up into sections that can be adjusted independently of each other. Rather than an iris closing down to dim the entire picture, the LEDs will manipulate brightness only to the portions of the image needed. In the 'Star Wars' example, the parts of the screen with the background of space in them can stay dark while the parts taken up by the spaceship brighten.
However, even this is still a compromise. Although more precisely targeted than a dynamic iris, local dimming still works on the same principle of reducing light output to achieve a darker picture. This will continue to have the consequence of crushing shadow detail. In a science fiction film where you see the darkness of space with stars in the far background, reducing light output to darken the black level will inevitably dim the stars (possibly to the point of crushing them out completely).
Dynamic contrast is essentially a trick. It can be an effective trick, but a display with high native contrast will always be superior. If contrast reproduction is a high priority for you, plasma or LCoS will probably be a better option than LCD. (Note that even plasma or LCoS may have dynamic contrast features enabled as well.) As a projector owner, my preference is for the D-ILA line from JVC (which is that company's variation on LCoS). D-ILA projectors have high native contrast without the need for dynamic enhancements.
Whatever you shop for, be sure to read product reviews from trusted sources before purchasing anything. You cannot take the contrast specifications provided by manufacturers at face value. Those listed specs are almost always measured in unrealistic situations that cannot be reproduced in the home at proper calibration values. A good product reviewer will measure the actual performance under realistic viewing conditions.
The HD Advisor knows many things, but he doesn't know everything. Some questions are best answered with a consensus of opinions from our readers. If you can help to answer the following question, please post your response in our forum thread linked at the end of this article. Your advice and opinions matter too!
Finding a Job in the Home Entertainment Industry
Q: Just before they went out of business, I was employed by Tweeter, selling high-def televisions and home entertainment systems. With the combination of dirt poor margins, the company's impending bankruptcy, and my generally crappy sales skills, I was unable to make a real living there. That lack of sales skill prevents me from attempting employment at other commission-based home theater companies. What I would like to do is find out how to gain employment in a different facet of the home entertainment industry. What kind of skills or degree would I need to look into a career in mastering or remastering movies or television shows for Blu-ray or streaming? Are there schools dedicated to training individuals on that career path? Is it even a career path that has the potential for future growth, considering the mainstream media's constant panic-stories concerning the decline in DVD sales? What of tangentially related careers, such as film restoration or the like, basically anything that wouldn't require sales skills on my part? Thank you for any information you can give on this!
Check back soon for another round of answers. Keep those questions coming.
Joshua Zyber's opinions are his own and do not necessarily reflect those of this site, its owners or employees.
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