ISO 00005-4:2009 pdf free download – Photography and graphic technology一 Density measurements一 Part 4: Geometric conditions for reflection density.
5 Distinction between ideal and realized parameters
The unambiguous definition of density requires that geometric, as well as spectral, parameters be exactly specified. However, the practical design and manufacture of instruments require that reasonable tolerances be allowed for physical parameters. The definition of ISO 5 standard reflection density shall be based on the ideal value specified for each parameter. The tolerances shown for the realized parameter values represent allowable variations of these standard parameters, which for many applications have an effect of less than 0,01 on the density values resulting from measurements made with instruments. A method for determining conformance of a realized parameter with the tolerances is given in Annex A.
6 Requirements
6.1 Influx and efflux geometry
ISO 5 standard reflection measurements may be made with two equivalent measurement geometries. In the “annular influx mode”, the geometry of the illuminator is annular and the geometry of the receiver is directional. In the “annular efflux mode”, the geometry of the illuminator is directional and the geometry of the receiver is annular. The annular influx mode is illustrated in Figure 1. The annular efflux mode would be illustrated by Figure 1 if the arrows showing the radiant flux direction were reversed and the labels were interchanged. The modes can be described in terms of specified annular and directional distributions of illumination radiance (subscript i) or receiver responsivity (subscript r), depending on the mode. The cone halfangle ic(lower case Greek kappa, is the angle between the angle of illumination or view (lower case Greek theta) and the marginal ray.
6.2 Sampling aperture
The extent and shape of the area on which density is measured are the sampling aperture. Physically, the sampling aperture is realized by the optical systems of the illuminator and receiver. The size and shape of the sampling aperture are not critical
a) if no dimension is so large that the influx and efflux geometric conditions vary materially over the sampling aperture, or
b) if no dimension is so small that the effects of granularity, specimen texture, diffraction, or half-tone dot structure become significant.
For case b), the diameter of a circular sampling aperture should not be less than 15 times the screen width; it shall not be less than 10 times the screen width that corresponds to the lower limit for the screen ruling for which the instrument is recommended by the manufacturer. The area of non-circular sampling apertures shall not be smaller than that required for circular sampling apertures.
The sampling aperture is defined as the smaller of the illuminator region and the receiver region. Ideally, the larger shall be greater than the smaller to the extent that any increase in size of the larger region has no effect on the measurement result. The specimen characteristics over the illuminator region should be the same as those over the receiver region.
NOTE I This requirement prevents lateral diffusion error.
The realized boundary of the larger of the illuminator region and the receiver region shall be outside the boundary of the smaller by at least 2 mm. Where small sampling apertures are required, this dimension shall be at least 0,5 mm. The magnitude of the resulting lateral diffusion error should be accepted as part of the overall measurement uncertainty, or a greater boundary differential should be used.