Brightness, resolution and contrast ratio are the headline characteristics of every projector – but they tell you very little about the image quality they will deliver in a given application.
In February, a debate about whether a woman’s dress was gold and white or blue and black became a worldwide internet phenomenon, with #TheDress top trending on Twitter. It provoked scientific debate about why people saw the online picture so differently – and reminded us that, whatever we might think, how we perceive images is an entirely subjective phenomenon.
For the AV industry, that argument provoked an interesting thought: in theory, two projectors with objectively identical characteristics in terms of brightness, resolution, contrast and so on should deliver a very similar image on the screen. But do they?
“I believe that it is almost impossible to determine the quality of a projector based on only a spec sheet,” says Romeo Baertsoen, VP of strategic marketing, corporate AV at Barco. “First of all, image quality is determined by many more parameters than are typically printed on a spec sheet. Secondly, manufacturers use different standards to measure different parameters, making it extremely difficult for customers to compare as you are no longer comparing apples to apples. Thirdly, some manufacturers have marketing specs and manufacturing specs – and the difference between the two can be 50%.”
Hartmut Kulessa, marketing manager, projector products at Panasonic, agrees. “Unfortunately, you can’t ascertain the quality of a projector by looking at the specification,” he claims. “Most people look at brightness, resolution and contrast when judging a projector’s spec – but the data provided is not always comparable. Panasonic always states ANSI lumen brightness, but you’ll also find manufacturers quoting centre lumens. Statements about contrast ratio can also be misleading as, very often, on-off contrast is given and this does not necessarily show how the projector performs with video and presentation content.”
“The specification of a projector gives top-line facts you need to know about the product,” says Phil Clark, head of projection at Casio Projectors, “but should these be relied upon to determine image quality? No. In reality, image quality depends on more than the simple specification of a projector.”
If Baertson, Kulessa and Clark are correct, questions about the value of a specification start to arise.
Paul Wilson, product manager for visual communications at Epson UK, puts it in perspective. “The core specification of a projector should give a good indication of image quality performance,” he believes. “The basic elements of brightness, resolution, contrast ratio, optics and connectivity should give a reasonable idea.”
Redressing an imbalance
However, it’s also imperative to have an appreciation of the way in which projectors are truly used, according to Wilson.
“The ANSI lumens rating for brightness is based purely on the reproduction of white light – which isn’t much use in reality as the majority of projected content is in colour,” he points out. “This is where the newer specification of Colour Light Output, or colour brightness, can be far more useful in judging the real-world performance of a projector.”
The Colour Light Output standard was developed to redress a perceived imbalance in that the ANSI standard inadvertently appeared to favour DLP-based projectors in terms of measuring brightness. The downside is, of course, that it is therefore not a standard universally adopted by the industry – making comparisons more difficult.
The brightness quoted on a data sheet can, it seems, not necessarily be taken as a true indicator of real-world performance – but it may be better, rather than worse.
“LED projectors outperform the brightness spec in real terms,” notes Justin Halls, head of product marketing at Optoma Europe. “For example, although Optoma’s HD91 has a brightness of just 1,000 LED lumens, the perceived brightness can be up to twice that of an equivalent lamp-based projector due to a phenomenon known as the Helmholtz-Kohlrausch (HK) effect.” [See boxout, below.]
If quoted brightness cannot entirely be trusted, the same is, apparently, no less true of contrast ratio. Some manufacturers quote ANSI contrast ratio, others peak contrast ratio – and still others dynamic contrast (allowing them to talk about ratios of 1,000,000:1 or more).
Once again, the specification is not necessarily an indicator of real-world performance. As Barco’s strategic marketing director, venues and hospitality, Richard Marples points out: in a high ambient-light environment, a projector with a quoted contrast ratio of 10,000:1 can easily drop down to a measured 20:1.
For Gerd Kaiser, product line manager, large-venue projectors at NEC Display Solutions, contrast is the least significant of the three primary image quality drivers. “The importance of contrast depends upon the application,” he says. “The most important elements are still brightness and resolution. While brightness has now reached a level which is sufficient for most applications, resolution continues to achieve more.”
It was to try to overcome inconsistencies of interpretation by manufacturers, and to acknowledge the realities of the different ways in which projectors can be deployed, that the ANSI/InfoComm 3M-2011 Projected Image System Contrast Ratio Standard (PISCR) was developed.