SMPTE RP 167-1995 Alignment of NTSC Color Picture Monitors.pdf

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1、SMPTE RP*167 95 8357401 O001921 322 SMPTE RECOMMENDED PRACTICE Alignment of NTSC Color Picture Monitors RP 167-1995 1 Scope 1.1 This practice describes an alignment proce- dure for the consistent and repeatable alignment of television color picture monitors. 1.2 For critical evaluation of picture pr

2、ogram material, the aligned monitor shall be used in an environment such as that described in SMPTE RP 166. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this practice. At the time of publication, the editions indica

3、ted were valid. All standards are subject to revision, and parties to agreements based on this practice are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. SMPTE EG 1-1 990, Alignment Color Bar Test Signal for Television Picture Monitor

4、s SMPTE RP 166-1995, Critical Viewing Conditions for Evaluation of Color Television Pictures 3 Test signals and equipment A video test signal generator providing the following signals shall be available: - SMPTE color bars with PLUGE (picture lineup generating equipment) signal (SMPTE EG 1) unmodula

5、ted gray scale (50% APL) - window signal (100 IRE), also variable in level - unmodulated variable-level flat field crosshatch - pulse and bar - multiburst - centrally placed full-field PLUGE signal Page 1 of 7 pages Ideally, a spectroradionieter is the optimum instru- ment for setting color temperat

6、ure. Operationally, a split-field optical comparator with a photometer and/or tristimulus (color analyzer) device is required. 4 Definition of terrns All color picture monitors are functionally similar, but the designation of the controls varies among models and manufacturers. (Refer to A.l for a li

7、sting of con- trols that perform similar functions.) 5 Alignment Although this practice specifies an operational align- ment procedure for television color picture monitors, other alignment procedures are equally valid if they achieve the desired result. All the steps are not required every time the

8、 color picture monitor is to be aligned. If the desired results cannot be obtained, then the corrective procedures suggested by the manu- facturer should be followed. If the color picture monit1x-s have an NTSC corrective matrix, the matrix shoulc be switched off during align- ment (see A.4). Alignm

9、ent procedures should be fol- lowed in the sequence ciiven below: - initial conditions (see 5.1) - initial screen adjustments (see 5.2) - display uniformity (!see 5.3) - scan size (see 5.4) - geometry and aspect ratio (see 5.5) - focus (see 5.6) - convergence (see 5.7) - aperture correction (see 5.8

10、) - chrominance ampli.:ude and phase (see 5.9) - brightness, color temperature, and gray-scale - monitor matching (see 5.11) tracking (see 5.1 O) Copyright O 1995 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W Hartsdale Ave., White Plains, NY 10607 (914) 761-1100 Approved February 1

11、 1, 1995 _ SMPTE RP*Lb7 95 8357403 O003922 2b9 = RP 167-1995 5.1 Initial conditions The color picture monitor should be turned on and allowed to stabilize for 20-30 minutes. The room ambient lighting should be the same as it is when the monitor is in normal service. Several minutes must be allowed f

12、or visual adaptation. All the color picture monitor controls should be in their preset positions. It is important that the aim luminance value, 120 cd/m2 (35 fL), be used for all the adjustments, except as noted. It is important that the comb filter and NTSC color matrix, if present, be defeated (se

13、e A.4). 5.2 Initial screen adjustments Switch the monitor to the setup position. In this mode, only horizontal lines or bars appear on the monitor screen. Adjust the red, green, and blue screen controls individually so that red, green, and blue signals are barely visible. These adjustments are only

14、preliminary and will be modified later to achieve correct gray-scale tracking (consult manufacturers procedures). 5.3 Display uniformity Good display uniformity is essential for color monitor matching. Perceptible variations in luminance levels or discolorations will make monitor matching difficult

15、or impossible. 5.3.1 Purity Purity is the ability of the gun to excite only its desig- nated phosphor. It is checked by applying a low-level flat-field signal and activating only one of the three guns at a time. The display should have no noticeable discolorations. Purity can also be checked by turn

16、ing the contrast control to minimum and increasing the brightness control until a medium bright red, green, or blue raster appears. If discolorations are perceptible, then appropriate corrective action should be taken; .e., degaussing, movement of purity magnets, etc. (see A.5). tangent to the mask

17、position. Overscan should be no more than 5% (see A.6). 5.5 Geometry and aspect ratio Geometry and aspect ratio of 4:3 are adjusted with the crosshatch signal by scanning the display device with the green beam only. Correct geometry and linearity are obtained by adjust- ing the pin-cushion and scan-

18、linearity controls so that the picture appears without evident distortions from the normal viewing distance. The following options are available: - place a linearity (ball chart) overlay onto the face of the CRT display; - project a linearity slide onto the CRT display with a high-quality slide proj

19、ector (a long focal length is required); - use a transparent linearity tape with 2% tolerance markings. 5.6 Focus An ideal focus target is not currently available on most test signal generators; however, multiburst, cross- hatch, or white noise can be used as tools to optimize the focus of the displ

20、ayed picture. The focus control should be adjusted at the aim luminance level with all the beams on for optimum picture resolution in the central areas of the picture. (There should be no noticeable loss of definition in the corners.) 5.7 Convergence Convergence is adjusted with a crosshatch signal.

21、 Convergence should be optimized for either normal scan or underscan, depending upon the application. The manufacturer generally provides an alignment sequence to ensure all scanning beams coincide. 5.4 Scan size 5.8 Aperture correction The color picture monitor application establishes whether the o

22、verscan or underscan presentation of the display will be selected. An underscanned display is one in which the active video (picture) area, includ- ing the corners of the raster, is visible within the screen mask. Normal scan brings the edges of the picture If aperture correction is used, the amount

23、 of aperture correction can be estimated visually by ensuring that the 2T sin2 pulse has the same brightness as the luminance bar or the multiburst signal when the 3 MHz and 4.2 MHz bursts have the same sharpness and Page 2 of 7 pages SMPTE RP*Lb7 95 M 8357403 O003923 IT5 contrast. This adjustment s

24、hould be verified under normal viewing conditions with picture material, not test signals (see A.7). 5.9 Chrominance amplitude and phase The chrominance amplitude and phase are adjusted using the SMPTE color bar test signal and viewing only the blue channel. Switching off the comb filter, if present

25、, provides a clear blue channel display (see A.8). The chroma set signal in the SMPTE color bar signal consists of four blue patches, which are to be matched with the four blue bars vertically above them. These blue bars and patches should increase and decrease in brightness equally, once the chromi

26、nance amplitude and phase controls have been properly set, as the contrast and brightness controls are varied over their normal range; .e., they should track (see A.8). Periodically, the red and green channels should be checked individually in a similar manner to verify that the decoders are working

27、 properly. 5.9.1 Visual alignment procedure A visual alignment procedure is given below: The left blue bar (blue component of the gray bar) is the reference bar and its brightness is affected only by the contrast control. The phase control affects the brightness of the inner two bars and patches. Th

28、e chroma control affects the brightness of the right outer bar and also the inner two bars. The adjustment sequence is first to adjust the chroma and then the phase so that all the bars and patches are of equal brightness and that black is interspersed between the blue bars. However, should the blue

29、 bars not track equally with a change in contrast, then the AFPC (automatic frequency and phase control) probably requires adjustment. Reduce the contrast until the blue bars and patches are barely visible. (The lefi-hand bar is the reference bar.) Adjust the phase control so that the right-hand blu

30、e bar matches the blue component of the gray patch. Then adjust the AFPC until the two center bars and patches are of equal brightness; the AFPC reacts in the same manner as the phase control. Slight readjustment of the chroma control to achieve uniform blue bars and patches may be necessary. Increa

31、se the contrast over its normal range. If the blue bars and patches do not track, repeat the above procedure with slight adjustments of the phase and/or AFPC. RP 167-1995 5.10 Brightness, color temperature, and gray- scale tracking The 100-IRE window signal is used to supply the reference white. Bls

32、cause of typical luminance shading limitations, a centrally-placed PLUGE signal is recommended for setting the monitor brightness control. However, until a centrally-placed PLUGE signal is commonly available, the PLUGE or black set signal provided in tie SMPTE color bars signal can also be used for

33、setting the monitor brightness control. (Refer to S. F. Ciuinn and C. A. Siocos. Pluge method of adjusting picture monitors in television studios - a technical note. J. SMPTE, 76: 925, September 1967.) 5.10.1 Reference white Using a split-field optical comparator, adjust the dis- played reference wh

34、ite to the illuminant D65 and a luminance value of 120 cd/m2 (35 fL) (see A.2). If the optical comparator has 3 variable luminance control, set the reference white on the monitor screen to the specified luminance value with a photometer and then adjust the comparator. Brightness, color temperature,

35、and gray-scale track- ing controls are interactive. Achieving all the correct results simultaneously requires adjustments which reduce but do not completely correct the perceived error(s). The adjustment sequence must be per- formed several times, each time with smaller incremental adjustment:;. 5.1

36、0.2 Preferred method An optical comparator is used to set the color tem- perature of the white pcht, using the monitor R,G,B gain controls. If the optical comparator does not have an output level equivaleiit to the reference luminance level, then it is necessary to adjust the contrast so that the wh

37、ite signal matches the brightness of the optical comparator. Gray-scale tracking is most easily set using a color photometer, but it must have adequate low-light sen- sitivity. The procedure is as follows: 1) Initialize the white point of the colorimeter using a 100-IRE window signal. 2) Reduce the

38、input sjignal to about 10-20 IRE. Page 3 of 7 pages SMPTE RP*Lb 75 357403 O003924 O31 m RP 167-1995 3) Adjust the monitor screen controls for matching RGB values as measured by the color photometer. 4) Using the PLUGE signal, set the brightness control so that the darker patch of the PLUGE just merg

39、es with the reference black level, but the brighter patch is clearly distinguishable from where the monitor will be normally viewed (see A.lO). 5) Readjust the input to a 1 00-IRE window signal. 6) Adjust RGB gain controls, as necessary, to obtain the reference white values. 7) Repeat steps (1) thro

40、ugh (6) until RGB measurements at both high- and low-luminance levels track closely. 8) Gray-scale tracking can be most accurately verified by measuring the color of the window pattern with the color photometer as the intensity of the window pattern is varied from the low-light IRE level through the

41、 middle steps of gray to 100 IRE. Avariable window will, in most cases, provide more accurate results than using a variable-intensity flat field. Alternatively, an unmodulated 50% APL stairstep signal can be used to verify gray-scale tracking throughout the displayed scale (see A.12). 5.10.3 Alterna

42、te method 1) Place the split-field optical comparator against the face of the monitor and over the center of the white area of the window pattern. Adjust the color picture monitor contrast control for a brightness match with the split-field optical comparator (see A.12). Adjust the red, green, and/o

43、r blue gain con- trols so that the monitor has a close match in color with the split-field optical comparator. 2) Display a 50% APL unmodulated stairstep signal. Then adjust the red, green, and/or blue screen controls to produce visual neutrals in the darker picture areas. 3) Using the PLUGE signal,

44、 set the brightness control so that the darker patch of the PLUGE just merges with the reference black level, but the brighter patch is clearly distinguishable from where the monitor will be normally viewed (see A.lO). 4) Repeat steps (1) to (3) for optimum results. The gray-scale signal (50% APL un

45、modulated stair- step signal) should now be visually neutral (black to white) and the reference white should have the desired color temperature and luminance value. 5.1 1 Monitor matching When color matching two or more color monitors, the same alignment steps should be performed on each monitor in

46、turn (see A.3). CAUTION - Monitors cannot be matched without the same phosphor sets, similar display uniformity characteristics, and similar sharpness, etc. (see A.14). The most noticeable faults on color monitors are the lack of uniform color presentations and brightness shading. Color matching of

47、monitors for these parameters can be most easily assessed by observ- ing flat-field uniformity of the picture at low, medium, and high amplitudes. Once monitor calibration has been satisfactorily completed in the monitors to be matched, apply an unmodulated flat field, first at a low level (15 to 30

48、 IRE), then at a mid-level (45 to 60 IRE), and finally at a high level (not to exceed 80 IRE), and observe the color and brightness changes over the entire sutface of the monitors to be matched. The patterns of non-uniformity in both intensity and color must be similar among the monitors, at all thr

49、ee levels, if average scene material displayed on these monitors are to match. There could be other reasons why the monitors do not match. Most often, the problems relate to incorrect adjustments, usually in this sequence: AFPC, color temperature and brightness of the reference white, and brightness control. Generating test patterns needed to determine the ability of monitors to match may be most easily accomplished in the studio by using the color background generator in the production switcher. It should have the capability of gener- ating the variable level luminance and