1、 STD-SMPTE RP L4-ENGL 3977 8357403 0002730 460 SMPTE RECOMMENDED PRACTICE Plotting Data from Sensitometric RP 14-1 997 Revision of RP 14-1988 Strips Exposed on Type Ib (Intensity Scale) Sensitometers 1 Scope The purpose of this practice is to specify the relation- ship of the spacings of the exposur
2、e scale (horizontal coordinate) of graph paper on which sensitometric data are plotted and the corresponding increments of the logarithm of exposure in the sensitometer when the exposure modulator is a step tablet. 2 Normative references The following standards contain provisions which, through refe
3、rence 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 the most recent edition of the
4、standards indicated below. ANSI/ISO 5-2-1 995, ANSVNAPM IT2.19-1995, Photography - Density Measurements - Part 2: Geometric Conditions for Transmission Density ANSI/ISO 5-3-1995, ANSI/NAPM IT2.18-1996, Photography - Density Measurements - Part 3: Spectral Conditions 3 Exposure method 3.1 In a type I
5、b (intensity scale) sensitometer, the most common method of modulating the illumination falling upon the sample employs a step tablet. The exposure is made with the emul- sion of the sample in contact with the modulator except for a thin, transparent acetate cover which protects the modulator agains
6、t abrasion and foreign matter. The opening and closing of a shutter admits light for the required period of time. Step tablets may be cast with gelatin Page 1 of 3 pages containing dyes or colloidal carbon or, alterna- tively, may be produced photographically by suitable exposure and development of
7、film or plates. 3.2 With a step tablet as the exposure modulator, the illumination reaching the sample is dependent upon the transmittance of the various steps of the modulator. This assumes uniformity of illumi- nation. Density, being the common logarithm of the reciprocal of the transmittance, is
8、a more convenient method for specifying the light- stopping power of the segments of the modulator. Density may be measured with a densitometer calibrated in reference to ANSI/ISO 5-2, ANSI/NAPM IT2.19, and ANSI/ISO 5-3, ANSVNAPM IT2.18. 3.3 The Ib (intensity scale) sensitometer exposure modulator s
9、hould typically have step- to-step increments of 0.1 5 diffuse transmission visual density; however, other increments can be used for specific needs. As modulators vary somewhat from this 0.15 increment, it may be necessary to adjust the step reference points on the exposure axis (horizontal coordin
10、ate) of the sensitometric graph paper to represent the actual densities of each step in the tablet. (Single step departures of the order of 0.01 5, or less, from the ideal 0.15 density increment, when known, would not be considered signifi- cant. However, cumulative errors, especially those which oc
11、cur in the same direction, are significant and can lead to erroneous results (see figure 1). 4 Method of correction 4.1 The steps of the exposure modulator shall be measured with a densitometer reading in dif- fuse transmission visual density, specified in Copyright O 1997 by the SOCIETY OF MOTION P
12、ICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (914)761-1100 Approved January 22,1997 RP 14-1 997 1.8 i .6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 o .o 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Dm NOTES 1 - - -x- - -x = curve showing sample densities versus m
13、odulator densities assumed to have consecutive ideal increments of 0.15. 2 -0-0- = curve showing same sample densities versus actual modulator densities for a modulator not meeting the criterion of 4.3 2). Figure 1 - Sample densities versus modulator densities ANSI/ISO 5-2, ANSI/NAPM IT2.19 and ANSI
14、/ISO 5-3, ANSVNAPM IT2.18. Such densities are normally shown on the calibration chart accompanying each new step tablet. 4.2 If such a calibration chart is not available, the step tablet should be removed carefully from the sensitometer and from its removable protec- tive cover, if any, and each ste
15、p read on a densitometer (see 4.1). 4.3 Unless the step tablet modulator conforms to the following specifications, the sensitometric density data shall be plotted against the actual rather than the nominal densities of the step tablet: 1) The density increment between any two adja- cent steps shall
16、be 0.1 50 f 0.01 5 density. 2) The departure of any step from its nominal density value shall not exceed 0.02 density or 2% of its density value, whichever is greater. The nomi- nal value is defined as the density of the lowest density step plus 0.15 times the number of steps above the lowest densit
17、y step. 3) No individual step shall depart from the best linear fit through all the steps by more than a density of 0.02. Page 2 of 3 pages STD-SMPTE RP 14-ENGL 1997 m 8357401 0002732 233 RP 14-1997 5 Method for plotting actual densities of the step-tablet modulator 5.1 For laboratories using graph
18、paper where the scale of the horizontal coordinate is as long or longer than the scale of the vertical coordinate: most laboratories carry a supply of printed graph sheets for the plotting of sensi- tometric data. These sheets normally carry a density scale on the vertical coordinate and a numbered
19、“step“ scale or log exposure reference on the horizontal coordinate. It is suggested that the density scale be cut off a graph sheet and placed along the horizontal co- ordinate of a second sheet. The scale of the first sheet should be oriented as shown in figure 1. 5.2 The density readings of the e
20、xposed and processed sample may now be plotted against the actual step-tablet densities. 5.3 For laboratories using graph paper where the horizontal coordinate is shorter than the vertical coordinate: on graph sheets where the horizontal coordinate carries 71/2 equal divisions between each “step“ or
21、 log exposure reference, each division represents 0.02 density of the sensitometer step tablet and may be used as reference to plot the densities of the step Annex A (informative) Bibliography tablet against the densities of the exposed and processed sample. 5.4 Where there is no scale on the horizo
22、ntal coordinate between each “step“ or log exposure reference, a scale may be drawn to divide the space between each reference into 7l/2 equal parts. Each part will represent 0.02 density of the sensitometer step tablet. This scale may be moved up the sheet opposite the various density readings of t
23、he exposed and processed sample so as to locate the step tablet densities versus the processed sample densities. 6 Care of the modulator 6.1 Step tablets are very delicate. To prevent damage, it is customary to protect the tablet with a thin, transparent acetate cover. The surface of the cover shoul
24、d be inspected from time to time to ensure that it is clean and free from abrasion. The acetate cover should be renewed when nec- essary to ensure that the diffuse transmission densities of the modulator steps are not affected by dirt or abrasion on the cover. 6.2 Although the density of step tablet
25、s normally changes little over periods ranging up to two years, it is suggested that the tablets be checked for density from time to time. Jones, Loyd A. Photographic sensitometry, Part I, January 1932; Part IV, Jour. SMPE 18:324-355, March Jour. SMPE 17r491-535, October 1931; Part II, Jour. SMPE 17:695-742, November 1931; Part 111, Jour. SMPE 18:54-89, 1932. Page 3 of 3 pages
