1、STD-SMPTE RP 15-ENGL 1997 8357LiOL 0002726 T3T M SMPTE RECOMMENDED PRACTICE Calibration of Densitometers Used for Black-and-white Photographic Density Measurements RP 15-1 997 Revision of RP 15-1988 1 Scope 1.1 The purpose of this practice is to specify the means to be employed in the calibration of
2、 densitometers utilized in the measurement of diffuse transmission densities. 1.2 This practice applies to densitometers utilized for the measurement of processed black- and-white photographic films and plates or cast colloidal carbon tablets. 2 Normative references The following standards contain p
3、rovisions which, through reference in this text, constitute provisions of this practice. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this practice are encouraged to investigate the possibility of applying th
4、e most recent edition of the standards indicated below. ANSIASO 5-2-1 995, ANSI/NAPM IT2.19-1995, Photography - Density Measurements - Part 2: Geometric Conditions for Transmission Density ANSI/ISO 5-3-1 995, ANSI/NAPM IT2.18-1996, Photography - Density Measurements - Part 3: Spectral Conditions 3 T
5、ypes of densitometers 3.1 In general, only those densitometers which conform to the geometric and spectral conditions specified by ANSVIS0 5-2, ANSVNAPM IT2.19 and ANSIASO 5-3, ANSVNAPM IT2.18 are capable of giving accurate readings of American Pagel of 4 pages National Standard diffuse transmission
6、 visual density for all types of black-and-white photo- graphic materials. 3.2 If a nonconforming densitometer is to be used with a given type of photographic material, it may be calibrated from reference samples composed of the same material. In this way, any densitometer may be calibrated to read
7、American National Standard diffuse transmission visual density, on any single type of photo- graphic material to a degree of accuracy com- mensurate with the stability and reproducibility of the instrument itself. In general, a new calibration must be made to obtain accurate readings on a different
8、material when a non- conforming densitometer is used. 4 Reference specimen 4.1 A reference specimen shall be a calibrated gray scale which is stored with special care and used at intervals of three months, more or less, as a primary reference against which to control the working specimens (see 5.1).
9、 4.2 A densitometer conforming to the geometric and spectral conditions specified in ANSMSO 5-2, ANSVNAPM IT2.19 and ANSIASO 5-3, ANSVNAPM IT2.18, and measuring in American National Standard diffuse transmission visual density, shall be used to calibrate the reference specimen. (Calibrated reference
10、 specimens are sold by manufacturers of densitometers, sensi- tometers, and film.) 4.3 The reference specimen shall have a range of diffuse transmission densities from below 0.06 to 3.0 or greater. Copyright O 1997 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., Whit
11、e Plains, NY 10607 (91 4) 761 -1 1 O0 Approved January 22,1997 STD-SMPTE RP 15-ENGL 1777 8357403 O002727 77b RP 15-1997 4.4 The density variation within each step or within each specified calibration area shall be 0.01 or less. (Care should be exercised in select- ing reference specimens. They shoul
12、d be free from dirt spots and abrasions. The step or cali- bration area should be large enough to accom- modate the largest aperture used for measuring the specimen and to allow for normal specimen- positioning variations. Good optical density stability is essential for reference specimens. In gener
13、al, this can be accomplished by keeping the processed specimen two months or longer under normal laboratory lighting and tempera- ture conditions before calibrating the specimen.) 4.5 A calibration chart shall accompany each reference specimen, giving the diffuse transmis- sion densities of each ste
14、p. It shall be noted on the calibration chart whether the diffuse trans- mission densities listed are American National Standard diffuse visual densities or American National Standard diffuse printing densities (ANSI/ISO 5-2, ANSI/NAPM IT2.19 and ANSVIS0 5-3, ANSVNAPM IT2.18). Each refer- ence speci
15、men and corresponding calibration chart shall be identified by a code or serial number. The chart shall also show the type of film of which the reference specimen is made. 4.6 Each step of each of three reference speci- mens shall then be measured carefully on the laboratory densitometer to be contr
16、olled. A mini- mum of 1 O step-by-step measurements should be made and each step averaged to establish the reference densities on the laboratory densi- tometers. The step-by-step measurements of one specimen shall be compared to the calibra- tion chart values for that specimen, and the deviations pl
17、otted versus the calibration chart values. (if, during the procedure, deviations in excess of the tolerances shown in 6.2 are obtained, the densitometer first could be cali- brated according to clause 6 and the procedure repeated. However, correlation curves obtained from a densitometer out of calib
18、ration, but oper- ating properly, are valid.) Measurements of each of the other specimens shall also be compared to corresponding calibration values, and the deviations plotted upon the same chart (see annex A). This procedure establishes the corre- lation among reference specimens. 4.7 The procedur
19、e in 4.6 shall be repeated on the same densitometer at three-month intervals. if the correlation among reference specimens remains the same, it can be assumed that the specimens have not deteriorated. (Even if used once a week for calibration, seasoned see 4.41 reference specimens, when properly han
20、dled, might be expected to remain in good condition for about a year.) 4.8 If the trimonthly check reveals that one specimen no longer correlates with the others, it shall be discarded. If the check shows that the samples have maintained their original correla- tion but all three deviation curves ha
21、ve shifted, it may be assumed that the instrument calibra- tion has changed. (However, it is remotely possible that all reference specimens have deteriorated equally.) 5 Working specimen 5.1 A working specimen shall be a calibrated gray scale which is used for the routine calibra- tion of densitomet
22、ers and measured for correct density against the reference specimens at inter- vals of three months, more or less. 5.2 For routine checking of the densitometer, it is not advisable to use the reference specimens. For this purpose, working specimens of the same material shall be used once they have b
23、een related directly or indirectly to the refer- ence specimens. 5.3 The working specimen can be directly related to the reference specimens by deviating initial average of replicate readings of the working specimen from those of a reference specimen calibration curve (4.6). These deviations, when p
24、lotted, shall constitute a working specimen cali- bration curve. The tolerances shown in 6.2 shall apply to the step values assigned to the working specimen. 5.4 The following alternate technique may be used in place of that outlined in 5.3: a working specimen may be selected and the step densities
25、read on a densitometer which has been newly calibrated by means of the reference specimens. When this working specimen is subsequently used to check densitometer calibration, the instrument shall duplicate the original readings Page 2 of 4 pages STD-SMPTE RP 15-ENGL 1997 m 8357901 0002728 802 within
26、 a tolerance of k 0.01 from density 0.00 to 2.0 and within f 0.02 above a density of 2.0. (These tolerances apply to electronic physical densitometers. Other densitometers may require wider tolerances. See 6.2 note.) If this tolerance is exceeded in the same direction by three successive steps in on
27、e calibration check or by one step on three successive calibration checks, the instrument shall be evaluated with reference specimens. If this evaluation shows the instru- ment to be in calibration, the new density values shall be assigned to the working specimen, or the working specimen shall be re
28、placed by a new one. If, however, the reference specimen con- firms that the instrument is out of calibration, it shall be recalibrated, as in clause 6. 6 Densitometer calibration 6.1 The reference specimen shall be placed in the densitometer to be calibrated in the manner specified in ANSI/ISO 5-2,
29、 ANSVNAPM IT2.19 and ANSVIS0 5-3, ANSVNAPM IT2.18; .e., the emulsion side of the reference specimen shall face the receiver, except that if the incident radiation is diffuse, the emulsion side of the specimen shall face the diffuser. (Reference specimens should be handled with care to pre- vent dens
30、ity changes resulting from abrasions, fingerprints, or foreign materials such as grease or film-cleaning compounds.) RP 15-1997 applications, tolerances may be allowed as follows: Density Tolerance 0.0 to 1.0 IO.01 1 .o to 2.0 2.0 to 3.0 f 0.02 3.0 to 4.0 f 0.03 1: 0.01 5 (see note) NOTE - It is imp
31、ossible to read thousandths of a density point on all but the most precise instruments. This figure is given as a tolerance based on the statistical average of several readings. Each individual densitometer will vary about its bias level. The amount of variation will depend upon the type and conditi
32、on of the instrument. Precision or repeatability of individual densitometers will determine the need for and degree of replication of measurements. 6.3 A densitometer which gives measured values with the reference specimen in excess of the tolerance in 6.2 shall be taken out of service for repair or
33、 adjustment. Alternatively, a correction table or chart may be utilized to permit adjust- ment of the measured values in accordance with the calibration chart. 6.4 If the densitometer under test is of the non- 6.2 The values of diffuse transmission density of conforming type, its scope may be evalua
34、ted by the type desired indicated by the densitometer measuring samples which vary in scattering under test shall agree with the values shown power and spectral selectivity and comparing the on the calibration chart accompanying the results with those obtained by the standard reference specimen. For
35、 routine sensitometric method. Page 3 of 4 pages Annex A (informative) American National Standard diffuse transmission visual density value 1 I I I I I I I I I I I I z p +.O3 a o +.o1 5 +.o2 W Eo - v) W z - .o1 o - .o2 - .O3 SPECIMEN DENSITY Figure A.l - Density deviations versus specimen density Page 4 of 4 pages
