Iec 61947 2 2001

INTERNATIONAL STANDARD IEC 61947 2 First edition 2001 09 Electronic projection – Measurement and documentation of key performance criteria – Part 2 Variable resolution projectors Reference number IEC[.]

Light output specifications

Light output specification for projectors with a separate screen

Light output measurement conditions: 6 500 K CCT, 4:3 aspect ratio, and a 2:1 HD6 lens;

(higher luminous flux values are better)

− 180 lm at 15,75 kHz horizontal and 90 Hz vertical;

− 220 lm at 36 kHz horizontal and 40 Hz vertical.

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Full-black light level specification

Measurements shall be made at the same signal as the black rectangles for contrast ratio measurement (see figure A.3).

− Full-black light level: 1,2 lm at 15,75 kHz horizontal and 90 Hz vertical.

Luminance specification for devices with an integral screen

Luminance measurement conditions: 9 300 K CCT, 4:3 aspect ratio, and a total screen viewing angle of 60° horizontal, 20° vertical (higher luminance values are better)

− 27 cd/m 2 (nit) at 15,75 kHz horizontal and 70 Hz vertical;

− 31 cd/m 2 at 33 kHz horizontal and 57 Hz vertical.

Direct comparisons of displays with and without integral screens can be accurately made using candela per square metre, provided that both screens share identical horizontal and vertical angles of view However, if the angles differ, mathematical conversions may be applied, but these will yield unreliable data of questionable value.

Light output uniformity

Example of a uniformity specification

− Brightest measurement locations: 10 % greater than average;

− Dimmest measurement locations: 5 % less than average.

Contrast ratio

The contrast ratio is calculated using illuminance or luminance values from a black-and-white "chessboard" pattern made up of 16 equal rectangles The white rectangles must be set to their maximum light output, with all controls maintained at the same settings.

Illuminance measurements, expressed in lux (candela per square metre with internal screen units), must be conducted at the center of both the bright (white) rectangles and the dark (black) rectangles.

To calculate the contrast ratio, divide the average illuminance or luminance of bright rectangles by that of dark rectangles This ratio is expressed as X:1; for instance, if bright rectangles have an average value of 15 lx and dark rectangles have an average value of 0.10 lx, the resulting contrast ratio is 150:1.

Blanking measurement and specification

The blanking (that portion of the raster that is forced to black to conceal the retrace or

In raster-scanned systems, the unblanked picture display time, defined as active horizontal time (\$T_{ah}\$) and active vertical time (\$T_{av}\$), is crucial for visual resolution calculations This display time is determined by subtracting the effective blanking time from the total scan time, ensuring that the blanking time is synchronized with the retrace time.

T ah is the active horizontal unblanked display time;

T sh is the horizontal scan time;

T ebh is the effective horizontal blanking time;

T av is the active vertical unblanked display time;

T sv is the vertical scan time;

T ebv is the effective vertical blanking time.

The effective blanking time shall be taken as the maximum time from the start of blanking or retrace to the end of blanking or retrace.

NOTE In some devices a retrace does not exist; for example, in laser projectors where a rotating polygon scanner is used as a horizontal deflector.

Effective blanking time

The effective blanking time shall be taken as the sum of the following:

− the out-of-phase time of the blanking and the retrace;

The maximum time for blanking or retrace is determined by adjusting controls such as hold, position, phase, and size.

− the unblanked picture display time that has a non-linearity greater than ±10 % compared to the centre of the screen.

When both the blanking and retrace times are 6.0 µs but are 0.5 µs out-of-phase, the effective blanking time becomes 6.5 µs This effective blanking occurs despite not being fully blanked due to factors such as component tolerances, frequency-sensitive circuitry, or phasing and centering control settings.

0,5 às, is the time that the video cannot usefully be viewed, either because it is actually blanked or because it occurs during retrace and is backwards and overlapped.

NOTE In some devices a retrace does not exist; for example, in laser projectors where a rotating polygon scanner is used as a horizontal deflector.

Blanking specification

Blanking (lower time values are better):

− horizontal blanking: 5,8 às or less;

− vertical blanking: 850 às or less.

The standard blanking specifications are not applicable to TV video inputs such as NTSC, PAL, and SECAM Instead, a unique blanking format is necessary for TV video to prevent unwanted signals like VIR, VITS, and closed captioning from appearing on the display It is recommended to utilize this specialized blanking format exclusively when displaying TV video content.

Visual resolution measurement and specification

Description and general requirements

The visual resolution specification enables users to directly relate the computer display to large screen displays, consisting of both horizontal and vertical resolution measurements.

The visual resolution specification refers to the count of unblanked pixels, determined by increasing pixel density until the modulation depth falls to 33% of the contrast measurement.

For devices with limited scan rate variability, an alternative procedure outlined in annex G must be followed to achieve an increase in pixel density.

The following formula shall determine the modulation depth:

L white and L black are luminance measured from full-screen white and black; and

L peak and L valley are peak and valley luminances measured from a grille pattern.

The measurements of L peak and L valley shall first be window-averaged over one pixel width

(to minimize sensor-noise effects), and shall then be averaged over all the peaks and valleys in the grille (to minimize grille aliasing effects).

NOTE 1 For more details on methodology, see the VESA Flat Panel Display Measurement Standard [4].

NOTE 2 Full white and black levels are measured with a large-area contrast test pattern (see figure A.3) The data used to determine the contrast can be reused here The modulation depth is the peak-to-peak measurement from the minimum light output (black) to the maximum light output (within the constraints of the light output measurement and specification) As the modulation depth decreases, the minimum light output may change to dark grey and the maximum light output may change to light grey The actual numbers are significant in this measurement only to establish the 100 % and 33 % points (see figure A.6).

Measurement of the modulation depth shall be made with the same conditions, control settings, and video levels as used in the light output specification by use of a pattern generator

(see annex B) with a test pattern of equal width (50 % duty cycle) white and black bars

Horizontal resolution

Horizontal resolution must be assessed using a high-resolution optical analyzer that can measure 1/10 the size of the smallest pixel at the specified image size determined by the display manufacturer Measurements should be taken perpendicular to the vertical parallel lines being evaluated (refer to figure A.4).

The pattern generator must be set to the maximum horizontal scan rate supported by the display device, while ensuring the vertical scan rate preserves the original size and aspect ratio of the image as outlined in section 3.4.

Vertical resolution

Vertical resolution is assessed using a high-resolution optical analyzer positioned perpendicularly to the horizontal parallel lines The pattern generator must be set to the lowest vertical scan rate allowed by the display device, while the horizontal scan rate should preserve the original size and aspect ratio of the image as specified in section 3.4.

If the vertical resolution limit is reached at a modulation depth greater than 33 %, the modulation depth percentage shall be stated along with the vertical resolution in the specifications.

NOTE 1 The vertical resolution may be limited by the maximum number of scan lines at the highest horizontal and lowest vertical scan rates and the vertical blanking time of the display This will be the maximum vertical resolution specification, regardless of any higher measurements which could be erroneous due to aliasing and line pairing.

NOTE 2 The lowest vertical scan rate may produce an objectionable flicker, depending on the persistence characteristics of the display.

Procedure

See figure A.6 for equipment set-up and the depth of modulation measurement example.

Conduct the test as follows.

The display system maintains consistent controls for black level (brightness), video gain (contrast), CCT image, and zoom settings, ensuring that illuminance and luminance measurements remain unaffected.

– The test generator is set to the chessboard rectangle pattern used in the contrast measurement where a full 100 % modulation can be measured (see figure A.3).

– The pattern is then changed to the resolution pattern of either the horizontal lines or the vertical lines (see figures A.4 and A.5).

The width of the lines is decreased, resulting in an increased number of lines at the generator, until the modulation depth of the measured display image reaches 33% of the value observed with the chessboard pattern, as illustrated in figure A.3 and figure A.6 This threshold is referred to as the 33% modulated pixel limit.

– Resolution measurements shall be made in each of the nine rectangular zones (see figure

A.2) and averaged Divide the amount of time that corresponds to the width of a single line at the 33 % modulated pixel limit into the active (unblanked) display time to yield the visual resolution in pixels Alternatively, the total number of both light and dark lines displayed at the 33 % modulation depth can be counted and reported.

– Visual resolution is then determined by specifying the number of pixels displayed at the

33 % modulated pixel limit, referring to horizontal or vertical resolution as appropriate.

In summary, to calculate the visual resolution,

– determine the unblanked display time (see 6.1.4.1 and 6.1.4.2 for examples of calculations of T ah and T av );

To determine the number of pixels visible during the unblanked display time, divide the unblanked display time by the pixel time at the 33% pixel limit, as illustrated in the example provided in section 6.1.4.3.

NOTE The unblanked display time may be measured with the pattern shown in figure A.1.

The horizontal unblanked display time is determined by subtracting the horizontal blanking time from the horizontal line time at the specified scan rate of the display being measured.

The vertical unblanked display time is determined by subtracting the vertical blanking time specification of the display from the vertical refresh time of the test generator.

6.1.4.1 Unblanked horizontal display time ( T ah ) calculation

If the test generator operates at a 15,748 kHz horizontal scan rate and the display’s horizontal blanking specification is 5,5 às, the unblanked horizontal line time is calculated as follows:

T ah = 63,5 às – 5,5 às = 58 às where 63,5 às is 1 s divided by the number of line scans per second (15,748 in this example).

6.1.4.2 Unblanked vertical display time ( T av ) calculation

If the test generator operates at a 60,0 Hz vertical scan rate and the display’s vertical blanking specification is 850 às, the unblanked vertical line time is calculated as follows:

T av = 1 666 às – 850 às = 816 às or 0,816 ms where 1 666 às is 1 s divided by the number of frames per second (60 in this example).

When the 33 % pixel limit is reached, the vertical lines are 55 ns black and 55 ns white, equivalent to 55 ns pixels The visual resolution can then be calculated as follows:

B = T ah /pixel time = 58 às/0,055 às = 1 055 pixels horizontal resolution where 58 às is the active display time of one line and 0,055 às equals 55 ns pixel time.

Visual resolution (both measurements made at the specified light output; higher pixel values are better):

− 1 055 pixels horizontal at 33 % modulation depth at 36 kHz;

− 1 024 pixels vertical at 42 % modulation depth at 40 Hz

6.1.4.5 Specification of multiple resolution and scan rate combinations

Visual resolution (measured at the specified light output; higher pixel values are better):

− 1 300 pixels horizontal at 33 % modulation depth at 64 kHz;

− 968 pixels horizontal at 33 % modulation depth at 31 kHz;

− 1 100 pixels vertical at 33 % modulation depth at 40 Hz;

− 1 024 pixels vertical at 42 % modulation depth at 60 Hz.

Video frequency response specifications

Frequency response specifications

Frequency response (rise and fall times of 28 ns measured with 10 % overshoot and 6 ns ringing):

− 35 MHz at –3 dB RGB video frequency response at the CRT cathode;

Viewing angle (half/gain) specification for devices with an integral screen

The viewing angle is defined as the angle between the normal to the center of the screen and the observer, measured in both horizontal and vertical directions It represents the range within which the intensity of luminance decreases to 50% of its maximum value For instance, a total screen viewing angle of 60° horizontally and 20° vertically indicates the full angle at which the intensity is at half its peak.

Input signal format compatibility

Manufacturers shall supply customers with a list of compatible modes, video standards and, if necessary, hardware description.

Response time

The response time shall be specified by the light valve manufacturer, for example, less than

50 ms for the photoelectric light valve.

Colour measurements

Colour chromaticity

To establish the desired Correlated Color Temperature (CCT), set up a white screen and measure the u′, v′ chromaticity across the nine zones of the screen, as illustrated in figure A.2, following the measurement procedure outlined in clause 5.

Similarly, set up a screen with the primary colours red, blue and green and measure the u′, v′ chromaticity of the centre of the screen.

A colour chromaticity example for a CCT of 6 500 K is as follows: white: u′= 0,198, v′= 0,468 red: u′= 0,477, v′= 0,528 green: u′= 0,076, v′= 0,576 blue: u′= 0,175, v′= 0,158

The "efficiency" of a color gamut can be determined by calculating the area of the triangle formed by the primary colors in the u′, v′ coordinate space and dividing it by the area defined by the spectrum locus in the same space For further details, refer to annex J.

Colour uniformity

Set up the screen to display white, red, green, and blue colors, and measure the u′ and v′ chromaticity values at the center of each of the nine equal rectangles shown in figure A.2.

Calculate the average chromaticity value (u′ 0 and v′ 0 ) of the nine measurements for each colour Also measure the u′, v′ chromaticity at the four corners of the screen.

To assess color uniformity, record the maximum deviation in $ u' $ and $ v' $ from the average values for each color across 13 measurements Let $ u'_{I} $ and $ v'_{I} $ denote the points with the highest deviation from the average values $ u'_{0} $ and $ v'_{0} $.

Keystone correction

Keystone correction refers to the range of angular tilt, measured in degrees, that allows a projector to display a rectangular image with equal top and bottom edges, as well as equal right and left edges This specification is crucial for ensuring that the projected image maintains its intended shape, even when the projector is not perfectly aligned with the screen.

Positive angles indicate that the screen centre-line orthogonal is above the projector,

(projection is up) Negative angles indicate that the screen centre-line orthogonal is below the projector (projection is down).

7 Range of focus and image size

This is the minimum and maximum distance from the screen from which a sharp focus and image size (diagonal) can be obtained.

Range of focus is 1,22 m to 4,27 m (4 feet to 14 feet) with a diagonal image size of 1,78 m to 3,05 m (70 inches to 120 inches) (4:3 aspect ratio).

The article discusses various audio input and output connections, detailing their impedance, signal levels, and connector types It highlights the selection methods for multiple audio/video inputs and specifies the signal isolation measured in decibels (dB) Additionally, it addresses special audio features, including stereo capabilities, to provide a comprehensive overview of audio connectivity options.

Report the power output and the frequency response in accordance with ISO 3741.

Output power when driving into an 8 Ω load is 5 W Total harmonic distortion for the frequency range 20 Hz to 20 kHz is less than 1 %.

If a lamp is used, the following information shall be reported:

– lamp wattage, CCT, and life expectancy (50 % or shutdown) (see 3.20);

– user or dealer serviceable lamp;

– any special handling requirements for safety.

If a CRT is used, the following information shall be required:

– life expectancy (when operated at levels used within the specifications).

Make the measurement in accordance with ISO 7779 and report the result.

NOTE Measurement could also be taken after 1 h of operation with all covers in place, white raster, as intended for normal use.

The projector must be connected to a stable power source, maintaining a voltage within ±0.5% of the nominal value Additionally, it is essential to report the power consumption, measured in watts, when the projector operates with all function controls set to their maximum power-consuming mode.

Also report the input voltage.

The weight (including that of the a.c power supply and specified lenses) shall be given in kg and/or pounds.

Length, width, and height shall be given in metres and/or inches.

Recommended practice 1 − Sync hierarchy

If the display device accepts more than one sync source, the following hierarchical preference should be used even if sync signals are present at more than one input:

− separate horizontal and vertical sync (5,0 V peak-to-peak video into 75 Ω);

− separate composite horizontal and vertical sync (5,0 V peak-to-peak video into

− composite sync mixed with the monochrome or green video (0,5 V peak-to-peak sync plus 0 V to 1,0 V peak-to-peak video into 75 Ω).

Recommended practice 2 − DC restoration

Annex A, figure A.7 outlines a black level clamp standard for display devices The specified 1.0 as horizontal sync and 2.0 as total blanking are expected to be sufficient for most future CRT-based, raster-scanned displays, given the challenges in achieving faster horizontal retrace times with the required magnetic deflection systems.

In situations where a "back porch" is not accessible for sampling and clamping, the display must be able to adjust the sampling point to the sync tip, either manually or automatically Additionally, it should offset the black level as necessary to ensure a consistent black background If the video signals lack sync, the initial edge of the horizontal sync can be utilized.

Recommended practice 3 − Sync

The deflection circuits must be activated by the initial edge of the input sync, which is the falling edge in standard negative sync systems and the rising edge in positive systems This edge marks the start of the blanked retrace time in the display, independent of the scan frequency Additionally, the horizontal deflection circuit should respond to the same edge of phase-correct, inverted sync pulses, referred to as equalization or serration pulses, during vertical sync.

The horizontal deflection circuits should accept a 1,0 às or larger sync pulse, separate or composite The vertical deflection circuit should accept a 180 às or larger sync pulse, separate or composite.

Recommended practice 4 − Scan range labelling

Multiscan displays should feature a small label near the input connections that indicates the horizontal and vertical scan rates, as well as the blanking times, similar to the example label illustrated in figure A.7.

Figure A.1 – Test patterns/measurements set-up

The pattern depicted in figure A.1 features a completely illuminating white design Each small rectangle has a height that is 10% of the image area's total height, while its width is proportionate to the overall dimensions.

5 % of the width of the image area; and the distance between two patterns is equal to 5 % of the height of the image area.

Figure A.2 – Thirteen-point measuring grid

Figure A.2 illustrates the nine measurement zones, with the center of each zone designated for assessing light output and visual resolution The corner points, labeled 10, 11, 12, and 13, are positioned at 10% of the distance from each corner to the center point 5.

Figure A.3 is a pattern of 16 rectangles of alternating white and black used to measure the large-area contrast ratio.

Figure A.4 is a pixel width pattern with alternating white and black vertical lines used for making the small-area contrast ratio measurement.

Figure A.5 is a pixel width pattern with alternating white and black horizontal lines used for making the small-area contrast ratio measurement.

Pa tte rn M eas uri n g devi c e M eas urem ent

Light sensor array Light sensor array

30 % Modulated pixel limit Full light

Modulated – Modulated black Full light – Full black × 100 = %

Figure A.6 – Resolution equipment set-up/depth of modulation measurement

Figure A.6 is an illustration of the configuration and reading of the optical measuring device used in figures A.4 or A.5.

H BCP 250 ns Black sample pulse

(a) Black sampling pulse relationship to the horizontal sync pulse when there is a minimum of 500 ns "back porch"

(b) Phase and width relationships of horizontal sync, horizontal equalization, and vertical sync

850 às (c) Suggested label format to be placed near the input connectors of multisync displays

Figure A.7 – Sync and blanking timing

The pattern generator needed for these measurements shall have as a minimum the following specifications.

– The ability to maintain output levels within 1 % when switching from pattern to pattern and during 8 h of operation.

– Three identical red, green, and blue outputs at 700 mV (±1 %), 75 Ω.

This device features a straightforward approach for inputting horizontal and vertical scan rates as separate frequencies Additionally, it includes automatic internal rounding to the nearest even vertical divisor and provides readouts in microseconds (µs).

The video pixel rates can be continuously adjusted to 50% on and 50% off (±1%), with pixel widths ranging from over 250 ns to under 5 ns Additionally, the rise and fall times must be less than 20% of the minimum pixel size, regardless of the chosen scan rates, with readout measurements provided in nanoseconds.

A pattern generator with a video pixel rate that exceeds the projector's specified capability can be utilized If the pattern generator does not meet this requirement, it is essential to provide a detailed description of the generator in the complete sample specification.

– Adjustable horizontal and vertical blanking and centring with readout in microseconds.

Resolution of the adjustments for blanking shall be at least as fine as 0,1 às of a micro- second (see figure A.1).

Considerations in formulating this standard

General

The intent of this standard is to codify the creation of uniform specifications that are useful to the non-expert user in the evaluation of large screen displays.

NOTE This concept correlates to the U.S Federal Trade Commission's (FTC) high-fidelity power and distortion measurement standards for the audio industry.

Light output measurement

Measuring the total luminous flux of a projector in lumens is essential for users to determine the illuminance of the projector and screen setup in various installations, as the screen type can vary in each application.

Screens come with gain values ranging from under 1 to over 20, and their viewing angles vary from 180° to below 20° The primary goal of any installation is to achieve a specific level of luminosity and contrast, which are influenced by factors beyond just the projector's luminous flux.

Illuminance (expressed in lux) is the luminous flux (expressed in lumens) from the projector incident on the surface per unit area (for example, square metre) of a projection screen.

Luminance, measured in candelas per square metre, quantifies the light intensity emitted from a surface It represents the luminous flux, such as lumens, per unit solid angle in steradians, relative to the area in square metres of the light source, and is assessed in a specific direction concerning a projection screen.

(for example, perpendicular to the screen).

A projector with an illuminance of 300 lx results in a screen luminance of approximately 95.5 cd/m², assuming a uniform light scattering and a screen gain of 1 For a projected image area of 1.8 m² on a lambertian screen, the light output is calculated to be 540 lumens, derived from both the projector's illuminance and the screen's luminance This equivalence is confirmed by the formula, where the screen luminance is multiplied by the image area and π, reflecting the half-space-integrated beam pattern of the lambertian screen.

In general, the light output for a lambertian screen having a gain of 1 may be computed as follows: Φ = π L A where: Φ is the luminous flux, in lumens;

L is the luminance, in candela per square metre;

A is the area of image, in square metres.

The selected pattern (refer to Annex A, Figure A.1) exemplifies modern workstations featuring black text on a white backdrop Ensuring the screen is fully illuminated is crucial, as it allows for clear visibility of the 5% and 95% illuminated rectangles.

Changes in the scan rate can significantly impact light output due to the fixed spot size When the spot size is small enough to fit 1,000 scan lines without overlap, a display with only 200 scan lines will result in a considerable amount of black, unscanned area The highest number of scan lines is achieved by combining maximum horizontal and minimum vertical scan rates, while the fewest scan lines occur with minimum horizontal and maximum vertical scan rates.

Visual resolution measurement

The resolution test procedure, defined by a modulation depth of approximately 33%, may produce more conservative results compared to traditional methods Previous measurements using 5% or 10% modulation depth are inadequate for today's small text and graphics The visual resolution specification aims to determine the pixel count necessary for characters and graphic symbols to be easily recognized by the target audience This 33% modulation depth parameter was established through empirical experimentation.

Artificially high numbers for resolution can be measured at greatly reduced light output in most

CRT-based projectors measure visual resolution at specified light output, avoiding the misleading practice of reporting inflated numbers at lower light levels Accurate resolution measurement relies on the precise specification of useful unblanked (active) video time, making it essential to define effective blanking accurately Additionally, reverse pixels during unblanked retrace can negatively impact picture quality.

Higher resolutions can be achieved beyond the visual resolution specification, but this may lead to decreased brightness, contrast, and edge definition The resolution is constrained by the bandwidth of the electronic circuit, the response behavior of the amplitude modulation of the beam, and the beam's shape Insufficient bandwidth results in reduced contrast in the scanned plane.

The comparison between horizontal and vertical line planes reveals that characters composed of multiple pixels can achieve a high modulation depth In contrast, adjacent single pixel characters often lack visibility due to their low modulation depth, leading to the vertical parts of characters becoming nearly invisible while the horizontal sections remain prominent (see figure C.1).

Possible causes for measurement errors

Even with careful setup of measurement and display conditions according to the standard, various factors can still cause measurement errors and significant discrepancies in light measurements of a projection system.

Issues to be watchful of are briefly discussed in clause 5 and in annexes F and H.

Input signal levels

Analogue input signal levels for R, G, and B should be 0,7 V.

Figure C.1 − Simulation of lowered resolution

XYZ brand, Model 123 data projector (specification based on July 1996 measurements)

Light output measured with 2:1 HD6 lens:

− Horizontal and vertical frequency or

Light output measured with 67-inch diagonal lenticular screen:

Full black light level: 1,2 lm

Light output uniformity (across image area)

Blanking time: 2 às minimum horizontal and 850 às minimum vertical

Resolution (pixels) at light output: 1 055 horizontal by 1 024 vertical

Frequency response (at the CRT cathode): 120 MHz (–3dB point) and –12 dB per octave roll-off

Response time (10 % – 90 %): 8 ns rise time and 10 ns fall time

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Audio: 5 W r.m.s audio power into an 8 Ω load; total harmonic distortion:

Tiêu đề	Electronic projection – Measurement and documentation of key performance criteria – Part 2: Variable resolution projectors
Trường học	International Electrotechnical Commission
Chuyên ngành	Electrical and Electronic Engineering
Thể loại	Standards document
Năm xuất bản	2001
Thành phố	Geneva

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