We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Fig. 1. Type 31A densitometer with strip holder and indexing mechanism. Separately mounted amplifier at right.
throughout the world, with very encouraging results.
Requirements
The functional requirements decided upon for the new densitometer were as follows :
1. Measurement of transmission density in narrow spectral regions defined by interchangeable color filters.
2. A direct-reading range of 0 to 4.
3. Measurement of integral density, that is, spectral density of the sample as a whole. Analytical densities, or the densities of individual dye components, can be deduced by a transformation process from integral densities measured at three wavelengths.2
4. Conformance of the readings, on all types of samples, with American Standard diffuse density.3 Briefly, this means illumination of the sample with nearly collimated light and collection of light emerging at all angles.
5. Adaptability to the widest possible range of uses, including graphic-arts applications, measurements on photographic plates, and rapid stepwise positioning and reading of sensitometric strips.
6. Freedom from drift and instability due to all causes, including line-voltage variations.
The necessity of measuring spectral densities up to 4 demands a higher instrument sensitivity than is immediately apparent, because of the necessarily low total transmittance of suitable color filters. A dye image may, for example, have a density of 4 at the wavelength of measurement and yet transmit quite freely over broad bands in the visible and infrared. In such cases, only a color filter having extremely high density outside the passband can attenuate sufficiently to prevent contamination of the measured flux. Narrow-band color filters having acceptable performance, such
K. G. Macleish: Color Densitometer
697