Display differences
Dear editor:
I know that many broadcast control rooms and mobile units are converting from CRTs to LCDs, LEDs and plasmas. I am interested in learning more robust information on the topic. Specifically, I'm looking for any information on the size of the market; market growth; what features, functions and inputs are important to this market; and how LCD, LED and plasmas differ between control rooms and mobile units.
Elizabeth Wolff
NEC Display Solutions
John Luff responds:
The main issues in broadcast-quality monitoring environments are colorimetry and stability, motion portrayal, contrast, image cut off light leakage (black level), aspect ratio, HD/SD compatibility, input options, calibration strategy, and cost. CRT broadcast monitors (called grade 1) historically have had highly repeatable colorimetry and the ability to be finely calibrated.
Other monitoring methods, including front projection, and emissive and transmissive displays, must be measured in comparison to the capabilities of CRTs. The feature set of current CRT monitors for professional use is likely to be replicated in any solution accepted as a true replacement.
A few manufacturers have begun to attempt to satisfy this market with non-CRT hardware, but not without resistance and skepticism in the market because of the technical capabilities of alternative technologies. I suspect that little public research has been done on the market issues you raise.
Features and controls should not be the primary concern. Mobile units and even some video control rooms are not the issue, either. I strongly believe that in sensitive markets, performance is the main issue. This includes camera shading, telecine operations and quality control. The disappearance of CRTs will be a major issue confronting the industry during the next several years. Most control rooms, trucks and fixed facilities are more concerned with picture composition and approximation of the image received by home viewers. In this regard, it is particularly difficult to make a selection, because home viewers today have a spectrum of choices, all of which create a matrix of production and viewing conditions that makes a single technology choice difficult to justify.
A resolution
Dear editor:
The data sheet for my Sony BVM-A20F1U monitor says that with a 16:9 picture, the raster will display 700 TV lines. If I install one of these monitors with the HD module and give it a 1920 × 1080/59.94/2:1 interlaced signal, will I only be able to see 700 lines of resolution? What about the other 380 lines? If I then give the monitor a 1280 × 720/59.94/1:1 progressive scan signal, will I see more of the picture? Does the Kell factor affect this? What exactly am I seeing on the screen? Do any displays show all 1080 active lines of a 1920 × 1080i signal?
Name withheld by request
John Luff responds:
Your question is timely as the interest in 1080p displays is rising in consumer circles. Resolution in lines per picture height is measured on the basis of alternating lines of black and white.
The Kell factor is certainly important. With 1080 active lines, the Kell factor reduces the maximum resolution for interlaced pictures to about 70 percent, or about 756 lines. Progressive scan does not suffer because every line is present on every frame.
One could argue that 720p is about the same perceived vertical resolution as 1080i. Horizontally, there is a huge difference, in theory at least, with 720p having two-thirds of the resolution. In practice, most compression systems subsample all inputs to about 1440 pixels, making the two standards essentially identical at the home receiver. However, 720p has better temporal resolution, with 60fps compared to 30fps for 1080i.
Progressive scan images are easier to compress, leading to better pictures for the same data rate. 1080p displays have interpolated the missing picture data because consumer interlace pictures don't contain the full production aperture of 1080p through DTV systems. I suggest producing in 1080p and keeping it that way if you want to see all 1080 lines.
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