HDTV & Front Projection Systems (part 2)
By Greg Rogers
For instance, a projector may specify an optical resolution of 1200 TVL, a video resolution of 1000 TVL and a RGB resolution of 1600x1200. In this case, the RGB resolution of 1600 pixels across the entire screen width would imply a video resolution of 1600 * 75% = 1200 TVL, the same as the optical resolution of the lens. But the best estimate of the actual maximum resolution on video pictures would be the lower of the specifications, or 1000 TVL. Furthermore, the specifications will assume the best possible setup of focus, astigmatism and convergence at a minimum acceptable light output to reduce the displayed spot size.
Projector resolution is a subjective measurement since it relies on a judgment call of when lines are resolvable or not. You can see the difficulty of this measurement for yourself by using your own judgment to specify the resolution of a monitor or projector using the resolution wedges included on the Video Essentials laserdisc or DVD. You will also see that the resolution will vary depending on the contrast setting, which alters the light output from the CRTs and therefore the spot size. Some projectors will hold their spot size with increases in brightness while others will defocus more quickly. Two projectors with the same subjective resolution at a low brightness level may measure much differently at higher and more realistic brightness levels. So keep this in mind when considering projector resolution specifications and get a direct comparison demonstration whenever possible.
Not withstanding the caveats expressed above, what is the maximum resolution performance of the HDTV formats? The 720P format has 1280 pixels across the width of the active picture area. The 1080I format has 1920 pixels from edge to edge of the picture area. Could an HDTV picture ever display that number of alternating black and while lines? Theoretically yes, but practically no. The video frequency content of the luminance signal must be limited to below the Nyquist frequency of the pixel sampling rate to avoid aliasing. If you look at the chart you will see that the pixel sampling rate is 74.25 MHz for both HDTV formats. The Nyquist frequency is one-half of the pixel sampling rate or 37.125 MHz.
If the pixels were alternating black and white, to form black and white vertical lines, then the frequency of the video signal would be exactly 1/2 of 74.25 MHz or 37.125 MHz. But to avoid any frequency components from exceeding this limit, the video signal is filtered prior to MPEG encoding. The filters can not have infinitely steep frequency band rejection, so they must filter out some frequencies considerably below the Nyquist limit. The ATSC standard specifies a virtually flat (+/- 0.05 dB) video frequency response to 30 MHz. A practical filter flat to 30 MHz might roll off into the video background noise within about 10% of that frequency. So I have chosen 33 MHz as the limiting bandwidth (the point where no additional high frequency detail can be seen). The 10% transition region is consistent with the performance observed for current DVD filtering.
Limiting Resolution per Picture Width = (Limiting Bandwidth / Nyquist Frequency) * Active Pixels per Picture Width
Limiting Resolution per Picture Height (4:3 Picture) = Limiting Resolution per Picture Width * 3/4
Limiting Resolution per Picture Height (16:9 Picture) = Limiting Resolution per Picture Width * 9/16
The limiting resolution for each format is shown in the table below.
Horizontal Resolution
Feature
NTSC
Composite
Digital
DVD
ITU-
R-601
DVD
Line
Doubled
DVD
Line
Quadrupled
ATSC
720P
ATSC
1080I
ATSC
1080I
Line Doubled
Frame Rate (Hz)
29.97
29.97
59.94
59.94
60
30
60
Field Rate (interlaced only) (Hz)
59.94
59.94
Progressive
Progressive
Progressive
59.94
Progressive
Active Picture Horizontal Pixels
768
720
720
720
1280
1920
1920
Pixel Clock Rate (MHz)
14.318
13.5
27.0
54.0
74.25
74.25
148.5
Video Signal Bandwidth
+/-0.05 dB BW (MHz)
Limiting BW (MHz)
-
4.2 RF
-
5.3 LD
5.75
6.3
11.5
12.6
23
25.2
30.0
33
30.0
33
60.0
66
Limiting Horiz Resolution per
Picture Width (TV Lines)
448 RF
567 LD
667
667
667
1138
1707
1707
Limiting Horiz Resolution/PH
(TVL for 4:3 display)
336 RF
424 LD
506
506
506
853
1280
1280
Limiting Horiz Resolution/PH
(TVL for 16:9 display)
N/A
380
380
380
640
960
960
Projector Bandwidth (-3 dB) (MHz)
10
10
20
40
50
50
100
A 4:3 display with a true 1000 lines of horizontal resolution (1333 lines across the full width) would have a CRT spot size, optical resolution and video bandwidth sufficient for 720P, but not enough to completely resolve the horizontal resolution of 1080I.
In terms of specifications used for 4:3 displays, the horizontal resolution would have to be at least 1707 * 3/4 = 1280 TVL to resolve all of the practical horizontal resolution information delivered by the 1080I format. The resolution would have to be 1440 TVL (1920 * 0.75) on a 4:3 display to fully resolve the theoretical maximum resolution of the 1080I format.
The 1280 TVL is beyond any current direct view CRT monitor, including Sony's professional BVM HDTV monitors. This is also beyond most CRT projectors. But CRT projectors with a true 1000 TV lines or more of horizontal resolution are still going to look just wonderful with an HDTV signal.
Video (RGB) Bandwidth
Bandwidth is closely related to horizontal resolution. Regardless of the CRT spot size and optical characteristics of the lenses, the RGB signals must arrive at the CRTs with sufficient bandwidth to modulate the beam current at a rate (frequency) that creates the high resolution light to dark transitions of the image. The frequency response of the projector's electronics will degrade the frequency bandwidth of the HDTV signals unless the projector bandwidth is considerably higher than the HDTV signal bandwidth. If that happens, horizontal picture resolution will be lost. The projector manufacturer's horizontal resolution specification should include any limitations from the projector's bandwidth. However, this is not always the case. So the video bandwidth, or more precisely the RGB bandwidth (video bandwidth is sometimes taken to mean the bandwidth through a composite or Y/C input), should be checked as an independent requirement.
Since both 1080I and 720P use the same sample rate, 74.25 MHz, they have the same specification for a flat frequency response to 30 MHz. The projector frequency response should also be flat within a fraction of a dB to 30 MHz. This means a projector bandwidth (which is usually specified at - 3 dB) of about 50 MHz should be adequate. However, each projector will have a somewhat different frequency response curve, so unless the bandwidth is 60 MHz or more you might want to ask the manufacturer for the response at 30-35 MHz.
To use a projector with an HD 1080I line doubler the frequency response of the projector should be flat to 60 MHz. This would require a projector with about a 100 MHz bandwidth.
Vertical Resolution
There are two factors that make the vertical resolution difference between the NTSC and ATSC formats even larger than it may appear. The ATSC numbers refer to the active picture area only. NTSC's 525 scan lines include about 42 lines that occur during the vertical blanking interval. This leaves about 483 lines for the active picture area. Secondly, the ATSC 720P and 1080I formats are 16:9 formats. If a 16:9 area is letterboxed within a 4:3 NTSC picture, as it often is on laserdiscs or some DVDs, then there are only about 360 scan lines within the 16:9 image area. So the ATSC 720P format has twice the vertical resolution of a 4:3 letterboxed picture.
The DVD's 16:9 ('anamorphic') format provides a 33% improvement in vertical resolution over the 4:3 letterboxed format. The 16:9 format has 480 horizontal scan lines in the 16:9 image. This is equivalent to a vertical resolution of 640 lines (480 * 4/3) for a 4:3 display height. The 720P HDTV format provides an additional 50% improvement over the DVD 16:9 format.
Moreover, the 720P ATSC format is progressive with 720 scan lines per frame repeated 60 times per second. Laserdiscs and DVDs display 60 interlaced fields per second. Each field contains only half of the total frame scan lines. A 16:9 image area has only 180 scan lines per field using the 4:3 letterboxed format and 240 scan lines using the 16:9 format. The low vertical resolution makes interlacing artifacts especially obvious whenever there is slight motion between fields. The ATSC 1080I format is also interlaced, but it has three times the vertical resolution of the 4:3 letterbox format.
The 1080I format puts a difficult demand on any display device. As I just indicated, it requires three times the vertical resolution of a SD 4:3 picture. For 1080I, this is equivalent to displaying 1440 scan lines on the full height of a 4:3 display (480 * 3 = 1080 * 4/3 = 1440). Very few projectors will have a spot size small enough to actually resolve each line individually, the basic definition of vertical resolution.
You might notice that the theoretical maximum 1080I horizontal resolution expressed in pixels/PH is 1080 (1920 * 9/16). This is the same as the nominal vertical resolution. When the horizontal and vertical resolutions (both expressed in picture heights) are the same, they are called "square pixel formats". Both the 1080I and 720P ATSC formats are square pixel formats.
Vertical Resolution
Feature
NTSC
Composite
Digital
DVD
ITU-
R-601
DVD
Line
Doubled
DVD
Line
Quadrupled
ATSC
720P
ATSC
1080I
ATSC
1080I
Line Doubled
Frame Rate (Hz)
29.97
29.97
59.94
59.94
60
30
60
Field Rate (interlaced only) (Hz)
59.94
59.94
Progressive
Progressive
Progressive
59.94
Progressive
Active Picture Lines/Frame
483
480
480
960
720
1080
1080
Active Picture Lines/Field
241.5
240
Progressive
Progressive
Progressive
540
Progressive
Vertical Resolution
Lines per Picture Height
for a 4:3 Display
* 16:9 'Anamorphic' Format
483
480
640 *
480
640 *
960
1280 *
960
1440
1440
I don't believe any manufacturer specifies the vertical resolution of their projectors as a separate line item. As I mentioned earlier, the RGB or computer resolutions that are sometimes specified, do not necessarily mean that each and every pixel can be resolved. So I would use caution in drawing too many conclusions from that data unless the manufacturer specifies that they are resolvable pixel resolutions.
In most cases the projector's vertical resolution for a 4:3 picture will be approximately the same as the horizontal resolution in TV Lines (referenced to a 4:3 picture height). This assumes that the spot size is approximately round (this will require good adjustment of astigmatism and focus) and that the horizontal resolution is not limited by the RGB bandwidth.
Only a handful of projectors will have sufficiently small spot sizes to truly display the full vertical resolution of the 1080I format. On the positive side, some modest overlapping of the scan lines will help hide the interlacing artifacts from this format. There is a very fine balancing act going on here that makes for the interesting debate between proponents of the 720P and 1080I formats. The 1080I format should produce a 50% improvement in horizontal and vertical resolution over 720P, but CRT and optical limitations in projectors (and aperture-grille and shadow-mask limitations in direct view TVs) will limit that significantly. But those same limitations partially obscure the visibility of the fine line-twitter and other interlace artifacts of the 1080I format. So the debate goes on between proponents of the 1080I and the 720P formats as the networks and others choose up sides for round one of HDTV.
Returning to the projector requirements, any projectors with conventional 4:3 horizontal resolutions of 1000 TV lines or more should display about all of the vertical and horizontal resolution that 720P has to offer. Projectors with 9" CRTs and premium lenses that can fully (or very nearly) resolve the full 1080I resolution will suffer more from the visibility of interlacing artifacts. These projectors will benefit from HD line doublers and should have the performance requirements discussed earlier to support them.
Two final notes on vertical resolution. First, the perceivable vertical resolution is significantly lower than the number of scan lines would indicate. This is related to the fact that the scan lines establish a discrete vertical sampling structure with finite scan line width (this is known as the aperture effect), as well as the fact that the scan lines may be interlaced. The measured loss of vertical resolution varies with the physical parameters of the display as well as the type of image used for evaluation. Several experimental evaluations of this phenomena have occurred over the years with varying results for perceived vertical resolution ranging from about 0.5-0.8 of the nominal scan line count. This is known as the Kell Factor and the figure most often used is 0.7.
Second, to help eliminate interline flicker on interlaced video, it is a common practice to vertically filter the output of the camera for video sources, or the telecine during film to video transfers. This filtering reduces interline flicker and shimmering by broadening the height of fine details to occupy more than a single scan line. Between the Kell Factor and deliberate vertical filtering, the perceived vertical resolution of an interlaced image may end up being little more than 50% of the nominal resolution found by counting the frame scan lines. In that case, the projectors spot size and optical resolution would seldom be a limiting factor.
Keep these last two considerations in mind when observing the nominal vertical resolution requirements given in the tables.
Summary of HDTV Parameters & Projector Requirements
Display Parameters for DTV Formats
Feature
NTSC
Composite
Digital
DVD
ITU-
R-601
DVD
Line
Doubled
DVD
Line
Quadrupled
ATSC
720P
ATSC
1080I
ATSC
1080I
Line Doubled
Frame Rate (Hz)
29.97
29.97
59.94
59.94
60
30
60
Field Rate (interlaced only) (Hz)
59.94
59.94
Progressive
Progressive
Progressive
59.94
Progressive
Aspect Ratio
4:3
4:3/16:9
4:3/16:9
4:3/16:9
16:9
16:9
16:9
Active Picture Horizontal Pixels
768
720
720
720
1280
1920
1920
Total Horizontal Pixels
910
858
858
858
1650
2200
2200
Active Picture Lines/Frame
483
480
480
960
720
1080
1080
Total Lines/Frame
525
525
525
1050
750
1125
1125
Horizontal Scan Rate (KHz)
15.734
15.734
31.468
62.937
45.0
33.75
67.5
Pixel Clock Rate (MHz)
14.318
13.5
27.0
54.0
74.25
74.25
148.5
Horizontal Retrace Time (uS)
9.92
10.22
5.11
2.55
4.98
3.77
1.89
Video Signal Bandwidth
+/-0.05 dB BW (MHz)
Limiting BW (MHz)
-
4.2 RF
-
5.3 LD
5.75
6.3
11.5
12.6
23
25.2
30.0
33
30.0
33
60.0
66
Projector Requirements for DTV Formats
Feature
NTSC
Composite
Digital
DVD
ITU-
R-601
DVD
Line
Doubled
DVD
Line
Quadrupled
ATSC
720P
ATSC
1080I
ATSC
1080I
Line Doubled
Horizontal Scan Rate (KHz)
15.734
15.734
31.468
62.937
45.0
33.75
67.5
Horizontal Retrace Time (uS)
9.92
10.22
5.11
2.55
4.98
3.77
1.89
Vertical Retrace Time (uS)
1335
1430
1430
1430
667
667
667
Projector Bandwidth (-3 dB) (MHz)
10
10
20
40
50
50
100
Limiting Horiz Resolution per
Picture Width (TV Lines)
448 RF
567 LD
667
667
667
1138
1707
1707
Limiting Horiz Resolution/PH
(TVL for 4:3 display)
336 RF
424 LD
506
506
506
853
1280
1280
Limiting Horiz Resolution/PH
(TVL for 16:9 display)
N/A
380
380
380
640
960
960
Vertical Resolution
Lines per Picture Height
for a 4:3 Display
* 16:9 'Anamorphic' Format
483
480
640 *
480
640 *
960
1280 *
960
1440
1440
Projector Specifications
Important
The following specifications for currently available projector models were assembled from the manufacturer's web pages. In many cases the information on their web pages is incomplete. There are also conflicting specifications on different web pages of the same manufacturer. In that case, I used the lower performance specification unless I thought there was an obvious error. I apologize for any errors in this table and invite manufacturers to submit corrections and additional information.
Different manufacturers may use different methods for measuring or stating the same specifications. Therefore, the specifications may not be directly comparable. This is particularly true in the case of the resolution specifications. Readers should always contact the projector manufacturers directly to verify and understand their specifications when making purchasing comparisons and decisions.
I've included several projectors in the table that are no longer current production models but are commonly available as used/refurbished products from dealers that advertise on the web. The specifications for those models were obtained from dealer web sites and private contacts. Refurbished products may include replacement components that are different than originally specified, and therefore the performance of these products may be better (or worse) than the original models. You should obtain a performance guarantee from your dealer.
CyberTheater assumes no responsiblility for the accuracy of the following specifications.
Projector Specifications
See notes at end of tablePrice
CRT
Light Output lumens peak
Horiz Scan Rate (Khz)
Horiz Retrace Time (uS)
Vert Retrace Time (uS)
Band
width (-3dB)
(Mhz)
RGB
Resolution
4:3 Display
Nominal or
Resolvable
Limiting
Horiz
Resolution
TVL/PH
4:3 Display
Lim Horiz
Res/PW
---- Vertical
Res/PH 4:3 Display
ATSC 720P
Requirements
45
4.98
667
50
853
1138
----
960
ATSC 1080I
Requirements
33.75
3.77
667
50
1280
1707
----
1440
Line doubled
1080P
Requirements
67.5
1.89
667
100
1280
1707
----
1440
Barco Graphics 1208s/
1209s
8"/9"
EMF
1000/
1050
135
1.25
200
120
Barco
Graphics
808s
8"
EMF
1050
110
2.5
200
120
1600x
1200
Barco
Data
808s
8"
EMF
1250
75
3.3
300
75
1180x
900
Barco
Vision1609
HDTV/
QDTV
9"
1600/
1050
64
3.3
300
60
CAL
Cinevision
IDP 950
7"
EMF
800
33.75
30
CAL
Cinevision
IDP 1050
7"
ESF
850
70
75
1600x
1200
Electrohome
Marquee 9500LC
9"
EMF
1300/
260 ANSI
130
1.8
300
120
2500x
2000 Addr
1500x
1200 Ansi
Electrohome
Marquee 8110/8500/
8500LC
8"
EMF
210/
225/
235
ANSI
110/
130/
130
1.8
300
100
2500x
2000 Addr
1350x
1100 Ansi
Electrohome
ECP Plus 4500/4501
7"
ESF
1005
150 ANSI
90
2.5
(5.0 below
37 KHz)
300
70
1600x
1280 Addr
1280x
1024 Resolvable
1024
Electrohome
ECP Plus 3500/3501
7"
ESF
1005
150 ANSI
72
3.6
300
60
1280x
1024 Resolvable
1024
Electrohome
ECP 4100
(Used Only)
7"
ESF
650
80
2.5
(5.0 below
37 KHz)
300
70
1280x
1024
1000
Electrohome
ECP 3100
(Used Only)
7"
ESF
650
50 or
58
3.6
300
60
1280x
1024
NEC
6PG
XTRA
7"
EMF
1000
69
2.5
350
100
1280x
1024
1200
NEC
XG75/ XG75A
8"
1100
230
ANSI
75
2.6
270
110
1500
NEC XG110LC
8"
1200
240
ANSI
110
2.6
270
120
2500x
2000 Addr
1500
NEC
XG135LC
$24K8"
1200
240
ANSI
135
2.6
270
150
2500x
2000 Addr
1500
Runco
DTV-852
w/Line Dbler
$15K
7"
EMF
850
50
Bypass doubler
50
900
Runco
IDP-980/950
$19K/
8"
EMF
1100
65
2.5
350
80
1600x
1200
1000
Runco
IDP-980
Ultra
$23K
8"
EMF1100
89
2.5
350
100
1600x
1200
1000
Runco
DTV-991/
Ultra
$25K/
$33K
8"
EMF
1200
75/
110
2.6
270
110
1600x
1200
2500x
2000
Runco
DTV-1000
$48K
9"
EMF
1250
135
1.25
200
120
2500x
2000
Sony
VPL W400Q
$5K
Three
1.35"
16:9
LCDs
400
ANSI
1080I
480I
only
800x480
4:3
1068x480
16:9
600
Sony
VPH D50Q
7"
800
64
75
1280x
1024
1000
Sony
VPH G70Q
8"
1200
110
120
1700x
1200
1100
Vidikron
Vision One
9"
130
Vidikron
VPH 50 HD
64
Vidikron
VPF 40 HD
55
Zenith
Pro900
$12.6K
800
50
1920x
1080
Zenith
Pro2000
w/Line Dbler
$20.5K
EMF
190 ANSI
1600x
1200
Projector Table Notes:
CRT
EMF - Electromagnetic Focus (EMF) generally provides a better spot size and more picture detail than Electrostatic Focusing.
ESF - Electrostatic Focus
Light Output
Peak Lumens - This is often measured by illuminating an area of about 10% the screen size in the center of the display. This measurement ignores the reduction in brightness at the sides and corners of the screen.
ANSI Lumens - Tested per an ANSI (American National Standards Institute) specification. The measurement is made by dividing the screen into 9 blocks, taking a reading in the center of each, and averaging the readings. This number is much lower than the peak lumen measurement (usually around 20-25%).
RGB Resolution
Nominal - This is the projector manufacturer's highest recommended computer resolution setting for use with their product. These are subjective recommendations and shouldn't be used for precise comparisons between products from different manufacturers.
Addr - Addressable, same as Nominal above.
ANSI (RGB/Computer Display) Resolution - This ANSI specification averages the measured resolution in nine different rectangular zones across the display and expresses the result in equivalent pixels across the picture width or height. The contrast between alternating black and white pixels is called the depth of modulation. The measurements are made by increasing the number of black and white lines (pixels) in the rectangular measurement zones until the depth of modulation drops below 30% of the large area contrast ratio.
Limiting Horizontal Resolution (for a 4:3 Display)
These specifications are almost always expressed in terms of TV Lines (alternating black and white vertical lines) across a display width equal to the picture height. This measurement is subjective, but if carefully made using normal picture operating conditions, it can be quite representative of actual performance.
Projector Table Notes:
CRT
EMF - Electromagnetic Focus (EMF) generally provides a better spot size and more picture detail than Electrostatic Focusing.
ESF - Electrostatic Focus
Light Output
Peak Lumens - This is often measured by illuminating an area of about 10% the screen size in the center of the display. This measurement ignores the reduction in brightness at the sides and corners of the screen.
ANSI Lumens - Tested per an ANSI (American National Standards Institute) specification. The measurement is made by dividing the screen into 9 blocks, taking a reading in the center of each, and averaging the readings. This number is much lower than the peak lumen measurement (usually around 20-25%).
RGB Resolution
Nominal - This is the projector manufacturer's highest recommended computer resolution setting for use with their product. These are subjective recommendations and shouldn't be used for precise comparisons between products from different manufacturers.
Addr - Addressable, same as Nominal above.
ANSI (RGB/Computer Display) Resolution - This ANSI specification averages the measured resolution in nine different rectangular zones across the display and expresses the result in equivalent pixels across the picture width or height. The contrast between alternating black and white pixels is called the depth of modulation. The measurements are made by increasing the number of black and white lines (pixels) in the rectangular measurement zones until the depth of modulation drops below 30% of the large area contrast ratio.
Limiting Horizontal Resolution (for a 4:3 Display)
These specifications are almost always expressed in terms of TV Lines (alternating black and white vertical lines) across a display width equal to the picture height. This measurement is subjective, but if carefully made using normal picture operating conditions, it can be quite representative of actual performance.
A special thanks to CyberTheater Productions LLC to for granting permission to post this informative article.
Projector resolution is a subjective measurement since it relies on a judgment call of when lines are resolvable or not. You can see the difficulty of this measurement for yourself by using your own judgment to specify the resolution of a monitor or projector using the resolution wedges included on the Video Essentials laserdisc or DVD. You will also see that the resolution will vary depending on the contrast setting, which alters the light output from the CRTs and therefore the spot size. Some projectors will hold their spot size with increases in brightness while others will defocus more quickly. Two projectors with the same subjective resolution at a low brightness level may measure much differently at higher and more realistic brightness levels. So keep this in mind when considering projector resolution specifications and get a direct comparison demonstration whenever possible.
Not withstanding the caveats expressed above, what is the maximum resolution performance of the HDTV formats? The 720P format has 1280 pixels across the width of the active picture area. The 1080I format has 1920 pixels from edge to edge of the picture area. Could an HDTV picture ever display that number of alternating black and while lines? Theoretically yes, but practically no. The video frequency content of the luminance signal must be limited to below the Nyquist frequency of the pixel sampling rate to avoid aliasing. If you look at the chart you will see that the pixel sampling rate is 74.25 MHz for both HDTV formats. The Nyquist frequency is one-half of the pixel sampling rate or 37.125 MHz.
If the pixels were alternating black and white, to form black and white vertical lines, then the frequency of the video signal would be exactly 1/2 of 74.25 MHz or 37.125 MHz. But to avoid any frequency components from exceeding this limit, the video signal is filtered prior to MPEG encoding. The filters can not have infinitely steep frequency band rejection, so they must filter out some frequencies considerably below the Nyquist limit. The ATSC standard specifies a virtually flat (+/- 0.05 dB) video frequency response to 30 MHz. A practical filter flat to 30 MHz might roll off into the video background noise within about 10% of that frequency. So I have chosen 33 MHz as the limiting bandwidth (the point where no additional high frequency detail can be seen). The 10% transition region is consistent with the performance observed for current DVD filtering.
Limiting Resolution per Picture Width = (Limiting Bandwidth / Nyquist Frequency) * Active Pixels per Picture Width
Limiting Resolution per Picture Height (4:3 Picture) = Limiting Resolution per Picture Width * 3/4
Limiting Resolution per Picture Height (16:9 Picture) = Limiting Resolution per Picture Width * 9/16
The limiting resolution for each format is shown in the table below.
| Feature | NTSC Composite Digital |
DVD ITU- R-601 |
DVD Line Doubled |
DVD Line Quadrupled |
ATSC 720P |
ATSC 1080I |
ATSC 1080I Line Doubled |
| Frame Rate (Hz) | 29.97 | 29.97 | 59.94 | 59.94 | 60 | 30 | 60 |
| Field Rate (interlaced only) (Hz) | 59.94 | 59.94 | Progressive | Progressive | Progressive | 59.94 | Progressive |
| Active Picture Horizontal Pixels | 768 | 720 | 720 | 720 | 1280 | 1920 | 1920 |
| Pixel Clock Rate (MHz) | 14.318 | 13.5 | 27.0 | 54.0 | 74.25 | 74.25 | 148.5 |
| Video Signal Bandwidth +/-0.05 dB BW (MHz) Limiting BW (MHz) |
- 4.2 RF - 5.3 LD |
5.75 6.3 |
11.5 12.6 |
23 25.2 |
30.0 33 |
30.0 33 |
60.0 66 |
| Limiting Horiz Resolution per Picture Width (TV Lines) |
448 RF 567 LD |
667 | 667 | 667 | 1138 | 1707 | 1707 |
| Limiting Horiz Resolution/PH (TVL for 4:3 display) |
336 RF 424 LD |
506 | 506 | 506 | 853 | 1280 | 1280 |
| Limiting Horiz Resolution/PH (TVL for 16:9 display) |
N/A | 380 | 380 | 380 | 640 | 960 | 960 |
| Projector Bandwidth (-3 dB) (MHz) | 10 | 10 | 20 | 40 | 50 | 50 | 100 |
A 4:3 display with a true 1000 lines of horizontal resolution (1333 lines across the full width) would have a CRT spot size, optical resolution and video bandwidth sufficient for 720P, but not enough to completely resolve the horizontal resolution of 1080I.
In terms of specifications used for 4:3 displays, the horizontal resolution would have to be at least 1707 * 3/4 = 1280 TVL to resolve all of the practical horizontal resolution information delivered by the 1080I format. The resolution would have to be 1440 TVL (1920 * 0.75) on a 4:3 display to fully resolve the theoretical maximum resolution of the 1080I format.
The 1280 TVL is beyond any current direct view CRT monitor, including Sony's professional BVM HDTV monitors. This is also beyond most CRT projectors. But CRT projectors with a true 1000 TV lines or more of horizontal resolution are still going to look just wonderful with an HDTV signal.
Video (RGB) Bandwidth
Bandwidth is closely related to horizontal resolution. Regardless of the CRT spot size and optical characteristics of the lenses, the RGB signals must arrive at the CRTs with sufficient bandwidth to modulate the beam current at a rate (frequency) that creates the high resolution light to dark transitions of the image. The frequency response of the projector's electronics will degrade the frequency bandwidth of the HDTV signals unless the projector bandwidth is considerably higher than the HDTV signal bandwidth. If that happens, horizontal picture resolution will be lost. The projector manufacturer's horizontal resolution specification should include any limitations from the projector's bandwidth. However, this is not always the case. So the video bandwidth, or more precisely the RGB bandwidth (video bandwidth is sometimes taken to mean the bandwidth through a composite or Y/C input), should be checked as an independent requirement.
Since both 1080I and 720P use the same sample rate, 74.25 MHz, they have the same specification for a flat frequency response to 30 MHz. The projector frequency response should also be flat within a fraction of a dB to 30 MHz. This means a projector bandwidth (which is usually specified at - 3 dB) of about 50 MHz should be adequate. However, each projector will have a somewhat different frequency response curve, so unless the bandwidth is 60 MHz or more you might want to ask the manufacturer for the response at 30-35 MHz.
To use a projector with an HD 1080I line doubler the frequency response of the projector should be flat to 60 MHz. This would require a projector with about a 100 MHz bandwidth.
Vertical Resolution
There are two factors that make the vertical resolution difference between the NTSC and ATSC formats even larger than it may appear. The ATSC numbers refer to the active picture area only. NTSC's 525 scan lines include about 42 lines that occur during the vertical blanking interval. This leaves about 483 lines for the active picture area. Secondly, the ATSC 720P and 1080I formats are 16:9 formats. If a 16:9 area is letterboxed within a 4:3 NTSC picture, as it often is on laserdiscs or some DVDs, then there are only about 360 scan lines within the 16:9 image area. So the ATSC 720P format has twice the vertical resolution of a 4:3 letterboxed picture.
The DVD's 16:9 ('anamorphic') format provides a 33% improvement in vertical resolution over the 4:3 letterboxed format. The 16:9 format has 480 horizontal scan lines in the 16:9 image. This is equivalent to a vertical resolution of 640 lines (480 * 4/3) for a 4:3 display height. The 720P HDTV format provides an additional 50% improvement over the DVD 16:9 format.
Moreover, the 720P ATSC format is progressive with 720 scan lines per frame repeated 60 times per second. Laserdiscs and DVDs display 60 interlaced fields per second. Each field contains only half of the total frame scan lines. A 16:9 image area has only 180 scan lines per field using the 4:3 letterboxed format and 240 scan lines using the 16:9 format. The low vertical resolution makes interlacing artifacts especially obvious whenever there is slight motion between fields. The ATSC 1080I format is also interlaced, but it has three times the vertical resolution of the 4:3 letterbox format.
The 1080I format puts a difficult demand on any display device. As I just indicated, it requires three times the vertical resolution of a SD 4:3 picture. For 1080I, this is equivalent to displaying 1440 scan lines on the full height of a 4:3 display (480 * 3 = 1080 * 4/3 = 1440). Very few projectors will have a spot size small enough to actually resolve each line individually, the basic definition of vertical resolution.
You might notice that the theoretical maximum 1080I horizontal resolution expressed in pixels/PH is 1080 (1920 * 9/16). This is the same as the nominal vertical resolution. When the horizontal and vertical resolutions (both expressed in picture heights) are the same, they are called "square pixel formats". Both the 1080I and 720P ATSC formats are square pixel formats.
| Feature | NTSC Composite Digital |
DVD ITU- R-601 |
DVD Line Doubled |
DVD Line Quadrupled |
ATSC 720P |
ATSC 1080I |
ATSC 1080I Line Doubled |
| Frame Rate (Hz) | 29.97 | 29.97 | 59.94 | 59.94 | 60 | 30 | 60 |
| Field Rate (interlaced only) (Hz) | 59.94 | 59.94 | Progressive | Progressive | Progressive | 59.94 | Progressive |
| Active Picture Lines/Frame | 483 | 480 | 480 | 960 | 720 | 1080 | 1080 |
| Active Picture Lines/Field | 241.5 | 240 | Progressive | Progressive | Progressive | 540 | Progressive |
| Vertical Resolution Lines per Picture Height for a 4:3 Display * 16:9 'Anamorphic' Format |
483 | 480 640 * |
480 640 * |
960 1280 * |
960 | 1440 | 1440 |
I don't believe any manufacturer specifies the vertical resolution of their projectors as a separate line item. As I mentioned earlier, the RGB or computer resolutions that are sometimes specified, do not necessarily mean that each and every pixel can be resolved. So I would use caution in drawing too many conclusions from that data unless the manufacturer specifies that they are resolvable pixel resolutions.
In most cases the projector's vertical resolution for a 4:3 picture will be approximately the same as the horizontal resolution in TV Lines (referenced to a 4:3 picture height). This assumes that the spot size is approximately round (this will require good adjustment of astigmatism and focus) and that the horizontal resolution is not limited by the RGB bandwidth.
Only a handful of projectors will have sufficiently small spot sizes to truly display the full vertical resolution of the 1080I format. On the positive side, some modest overlapping of the scan lines will help hide the interlacing artifacts from this format. There is a very fine balancing act going on here that makes for the interesting debate between proponents of the 720P and 1080I formats. The 1080I format should produce a 50% improvement in horizontal and vertical resolution over 720P, but CRT and optical limitations in projectors (and aperture-grille and shadow-mask limitations in direct view TVs) will limit that significantly. But those same limitations partially obscure the visibility of the fine line-twitter and other interlace artifacts of the 1080I format. So the debate goes on between proponents of the 1080I and the 720P formats as the networks and others choose up sides for round one of HDTV.
Returning to the projector requirements, any projectors with conventional 4:3 horizontal resolutions of 1000 TV lines or more should display about all of the vertical and horizontal resolution that 720P has to offer. Projectors with 9" CRTs and premium lenses that can fully (or very nearly) resolve the full 1080I resolution will suffer more from the visibility of interlacing artifacts. These projectors will benefit from HD line doublers and should have the performance requirements discussed earlier to support them.
Two final notes on vertical resolution. First, the perceivable vertical resolution is significantly lower than the number of scan lines would indicate. This is related to the fact that the scan lines establish a discrete vertical sampling structure with finite scan line width (this is known as the aperture effect), as well as the fact that the scan lines may be interlaced. The measured loss of vertical resolution varies with the physical parameters of the display as well as the type of image used for evaluation. Several experimental evaluations of this phenomena have occurred over the years with varying results for perceived vertical resolution ranging from about 0.5-0.8 of the nominal scan line count. This is known as the Kell Factor and the figure most often used is 0.7.
Second, to help eliminate interline flicker on interlaced video, it is a common practice to vertically filter the output of the camera for video sources, or the telecine during film to video transfers. This filtering reduces interline flicker and shimmering by broadening the height of fine details to occupy more than a single scan line. Between the Kell Factor and deliberate vertical filtering, the perceived vertical resolution of an interlaced image may end up being little more than 50% of the nominal resolution found by counting the frame scan lines. In that case, the projectors spot size and optical resolution would seldom be a limiting factor.
Keep these last two considerations in mind when observing the nominal vertical resolution requirements given in the tables.
Summary of HDTV Parameters & Projector Requirements
| Feature | NTSC Composite Digital |
DVD ITU- R-601 |
DVD Line Doubled |
DVD Line Quadrupled |
ATSC 720P |
ATSC 1080I |
ATSC 1080I Line Doubled |
| Frame Rate (Hz) | 29.97 | 29.97 | 59.94 | 59.94 | 60 | 30 | 60 |
| Field Rate (interlaced only) (Hz) | 59.94 | 59.94 | Progressive | Progressive | Progressive | 59.94 | Progressive |
| Aspect Ratio | 4:3 | 4:3/16:9 | 4:3/16:9 | 4:3/16:9 | 16:9 | 16:9 | 16:9 |
| Active Picture Horizontal Pixels | 768 | 720 | 720 | 720 | 1280 | 1920 | 1920 |
| Total Horizontal Pixels | 910 | 858 | 858 | 858 | 1650 | 2200 | 2200 |
| Active Picture Lines/Frame | 483 | 480 | 480 | 960 | 720 | 1080 | 1080 |
| Total Lines/Frame | 525 | 525 | 525 | 1050 | 750 | 1125 | 1125 |
| Horizontal Scan Rate (KHz) | 15.734 | 15.734 | 31.468 | 62.937 | 45.0 | 33.75 | 67.5 |
| Pixel Clock Rate (MHz) | 14.318 | 13.5 | 27.0 | 54.0 | 74.25 | 74.25 | 148.5 |
| Horizontal Retrace Time (uS) | 9.92 | 10.22 | 5.11 | 2.55 | 4.98 | 3.77 | 1.89 |
| Video Signal Bandwidth +/-0.05 dB BW (MHz) Limiting BW (MHz) |
- 4.2 RF - 5.3 LD |
5.75 6.3 |
11.5 12.6 |
23 25.2 |
30.0 33 |
30.0 33 |
60.0 66 |
| Feature | NTSC Composite Digital |
DVD ITU- R-601 |
DVD Line Doubled |
DVD Line Quadrupled |
ATSC 720P |
ATSC 1080I |
ATSC 1080I Line Doubled |
| Horizontal Scan Rate (KHz) | 15.734 | 15.734 | 31.468 | 62.937 | 45.0 | 33.75 | 67.5 |
| Horizontal Retrace Time (uS) | 9.92 | 10.22 | 5.11 | 2.55 | 4.98 | 3.77 | 1.89 |
| Vertical Retrace Time (uS) | 1335 | 1430 | 1430 | 1430 | 667 | 667 | 667 |
| Projector Bandwidth (-3 dB) (MHz) | 10 | 10 | 20 | 40 | 50 | 50 | 100 |
| Limiting Horiz Resolution per Picture Width (TV Lines) |
448 RF 567 LD |
667 | 667 | 667 | 1138 | 1707 | 1707 |
| Limiting Horiz Resolution/PH (TVL for 4:3 display) |
336 RF 424 LD |
506 | 506 | 506 | 853 | 1280 | 1280 |
| Limiting Horiz Resolution/PH (TVL for 16:9 display) |
N/A | 380 | 380 | 380 | 640 | 960 | 960 |
| Vertical Resolution Lines per Picture Height for a 4:3 Display * 16:9 'Anamorphic' Format |
483 | 480 640 * |
480 640 * |
960 1280 * |
960 | 1440 | 1440 |
Projector Specifications
Important
The following specifications for currently available projector models were assembled from the manufacturer's web pages. In many cases the information on their web pages is incomplete. There are also conflicting specifications on different web pages of the same manufacturer. In that case, I used the lower performance specification unless I thought there was an obvious error. I apologize for any errors in this table and invite manufacturers to submit corrections and additional information.
Different manufacturers may use different methods for measuring or stating the same specifications. Therefore, the specifications may not be directly comparable. This is particularly true in the case of the resolution specifications. Readers should always contact the projector manufacturers directly to verify and understand their specifications when making purchasing comparisons and decisions.
I've included several projectors in the table that are no longer current production models but are commonly available as used/refurbished products from dealers that advertise on the web. The specifications for those models were obtained from dealer web sites and private contacts. Refurbished products may include replacement components that are different than originally specified, and therefore the performance of these products may be better (or worse) than the original models. You should obtain a performance guarantee from your dealer.
CyberTheater assumes no responsiblility for the accuracy of the following specifications.
See notes at end of table |
Price |
CRT |
Light Output lumens peak |
Horiz Scan Rate (Khz) |
Horiz Retrace Time (uS) |
Vert Retrace Time (uS) |
Band width (-3dB) (Mhz) |
RGB Resolution 4:3 Display Nominal or Resolvable |
Limiting Horiz Resolution TVL/PH 4:3 Display |
Lim Horiz Res/PW ---- Vertical Res/PH 4:3 Display |
ATSC 720P Requirements |
45 |
4.98 |
667 |
50 |
853 |
1138 ---- 960 |
||||
| ATSC 1080I Requirements |
33.75 |
3.77 |
667 |
50 |
1280 |
1707 ---- 1440 |
||||
| Line doubled 1080P Requirements |
67.5 |
1.89 |
667 |
100 |
1280 |
1707 ---- 1440 |
||||
| Barco Graphics 1208s/ 1209s |
8"/9" EMF |
1000/ 1050 |
135 |
1.25 |
200 |
120 |
||||
| Barco Graphics 808s |
8" EMF |
1050 |
110 |
2.5 |
200 |
120 |
1600x 1200 |
|||
| Barco Data 808s |
8" EMF |
1250 |
75 |
3.3 |
300 |
75 |
1180x 900 |
|||
| Barco Vision1609 HDTV/ QDTV |
9" |
1600/ 1050 |
64 |
3.3 |
300 |
60 |
||||
| CAL Cinevision IDP 950 |
7" EMF |
800 |
33.75 |
|
|
30 |
||||
| CAL Cinevision IDP 1050 |
7" ESF |
850 |
70 |
|
|
75 |
1600x 1200 |
|||
| Electrohome Marquee 9500LC |
9" EMF |
1300/ 260 ANSI |
130 |
1.8 |
300 |
120 |
2500x 2000 Addr 1500x 1200 Ansi |
|||
| Electrohome Marquee 8110/8500/ 8500LC |
8" EMF |
210/ 225/ 235 ANSI |
110/ 130/ 130 |
1.8 |
300 |
100 |
2500x 2000 Addr 1350x 1100 Ansi |
|||
| Electrohome ECP Plus 4500/4501 |
7" ESF |
1005 150 ANSI |
90 |
2.5 (5.0 below 37 KHz) |
300 |
70 |
1600x 1280 Addr 1280x 1024 Resolvable |
1024 |
||
| Electrohome ECP Plus 3500/3501 |
7" ESF |
1005 150 ANSI |
72 |
3.6 |
300 |
60 |
1280x 1024 Resolvable |
1024 |
||
| Electrohome ECP 4100 (Used Only) |
7" ESF |
650 |
80 |
2.5 (5.0 below 37 KHz) |
300 |
70 |
1280x 1024 |
1000 |
||
| Electrohome ECP 3100 (Used Only) |
7" ESF |
650 |
50 or 58 |
3.6 |
300 |
60 |
1280x 1024 |
|||
| NEC 6PG XTRA |
7" EMF |
1000 |
69 |
2.5 |
350 |
100 |
1280x 1024 |
1200 |
||
| NEC XG75/ XG75A |
8" |
1100 230 ANSI |
75 |
2.6 |
270 |
110 |
1500 |
|||
| NEC XG110LC |
8" |
1200 240 ANSI |
110 |
2.6 |
270 |
120 |
2500x 2000 Addr |
1500 |
||
| NEC XG135LC |
$24K |
8" |
1200 240 ANSI |
135 |
2.6 |
270 |
150 |
2500x 2000 Addr |
1500 |
|
| Runco DTV-852 w/Line Dbler |
$15K |
7" EMF |
850 |
50 Bypass doubler |
50 |
900 |
||||
| Runco IDP-980/950 |
$19K/ |
8" EMF |
1100 |
65 |
2.5 |
350 |
80 |
1600x 1200 |
1000 |
|
| Runco IDP-980 Ultra |
$23K |
8" EMF |
1100 |
89 |
2.5 |
350 |
100 |
1600x 1200 |
1000 |
|
| Runco DTV-991/ Ultra |
$25K/ $33K |
8" EMF |
1200 |
75/ 110 |
2.6 |
270 |
110 |
1600x 1200 2500x 2000 |
||
| Runco DTV-1000 |
$48K |
9" EMF |
1250 |
135 |
1.25 |
200 |
120 |
2500x 2000 |
||
| Sony VPL W400Q |
$5K |
Three 1.35" 16:9 LCDs |
400 ANSI |
1080I 480I only |
800x480 4:3 1068x480 16:9 |
600 |
||||
| Sony VPH D50Q |
7" |
800 |
64 |
75 |
1280x 1024 |
1000 |
||||
| Sony VPH G70Q |
8" |
1200 |
110 |
120 |
1700x 1200 |
1100 |
||||
| Vidikron Vision One |
9" |
130 |
||||||||
| Vidikron VPH 50 HD |
64 |
|||||||||
| Vidikron VPF 40 HD |
55 |
|||||||||
| Zenith Pro900 |
$12.6K |
800 |
50 |
1920x 1080 |
|
|||||
| Zenith Pro2000 w/Line Dbler |
$20.5K |
EMF |
190 ANSI |
1600x 1200 |
Projector Table Notes:
CRT
EMF - Electromagnetic Focus (EMF) generally provides a better spot size and more picture detail than Electrostatic Focusing.
ESF - Electrostatic Focus
Light Output
Peak Lumens - This is often measured by illuminating an area of about 10% the screen size in the center of the display. This measurement ignores the reduction in brightness at the sides and corners of the screen.
ANSI Lumens - Tested per an ANSI (American National Standards Institute) specification. The measurement is made by dividing the screen into 9 blocks, taking a reading in the center of each, and averaging the readings. This number is much lower than the peak lumen measurement (usually around 20-25%).
RGB Resolution
Nominal - This is the projector manufacturer's highest recommended computer resolution setting for use with their product. These are subjective recommendations and shouldn't be used for precise comparisons between products from different manufacturers.
Addr - Addressable, same as Nominal above.
ANSI (RGB/Computer Display) Resolution - This ANSI specification averages the measured resolution in nine different rectangular zones across the display and expresses the result in equivalent pixels across the picture width or height. The contrast between alternating black and white pixels is called the depth of modulation. The measurements are made by increasing the number of black and white lines (pixels) in the rectangular measurement zones until the depth of modulation drops below 30% of the large area contrast ratio.
Limiting Horizontal Resolution (for a 4:3 Display)
These specifications are almost always expressed in terms of TV Lines (alternating black and white vertical lines) across a display width equal to the picture height. This measurement is subjective, but if carefully made using normal picture operating conditions, it can be quite representative of actual performance.
Projector Table Notes:
CRT
EMF - Electromagnetic Focus (EMF) generally provides a better spot size and more picture detail than Electrostatic Focusing.
ESF - Electrostatic Focus
Light Output
Peak Lumens - This is often measured by illuminating an area of about 10% the screen size in the center of the display. This measurement ignores the reduction in brightness at the sides and corners of the screen.
ANSI Lumens - Tested per an ANSI (American National Standards Institute) specification. The measurement is made by dividing the screen into 9 blocks, taking a reading in the center of each, and averaging the readings. This number is much lower than the peak lumen measurement (usually around 20-25%).
RGB Resolution
Nominal - This is the projector manufacturer's highest recommended computer resolution setting for use with their product. These are subjective recommendations and shouldn't be used for precise comparisons between products from different manufacturers.
Addr - Addressable, same as Nominal above.
ANSI (RGB/Computer Display) Resolution - This ANSI specification averages the measured resolution in nine different rectangular zones across the display and expresses the result in equivalent pixels across the picture width or height. The contrast between alternating black and white pixels is called the depth of modulation. The measurements are made by increasing the number of black and white lines (pixels) in the rectangular measurement zones until the depth of modulation drops below 30% of the large area contrast ratio.
Limiting Horizontal Resolution (for a 4:3 Display)
These specifications are almost always expressed in terms of TV Lines (alternating black and white vertical lines) across a display width equal to the picture height. This measurement is subjective, but if carefully made using normal picture operating conditions, it can be quite representative of actual performance.
A special thanks to CyberTheater Productions LLC to for granting permission to post this informative article.