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.
have certainly borne out our highest hopes, and incidentally have greatly increased the luminosity of the pictures. The absorption of the matrix or reseau has been reduced from over 90 per cent. to about 65 per cent., thus making the light transmitted nearly 34 times greater.
To return now to the emulsion. This must be capable of giving the intensity of black of a processemulsion, and yet must have a perfect scale of gradation corresponding to the whole of the light intensities usedin making apicture. Thoseinterested in sensitometry will appreciate the fact that, with so much light absorbed by the reseau, the inertia effect would become very pronounced in the shadows if the characteristic curve in the emulsion were to have a long foot. I have a diagram showing the characteristic curve of the Spicer-Dufay emulsion as against the classic S-shaped curve of MHiirter & Driffield.
The next slide shows how, after the original image is dissolved out by acid bichromate or acid permanganate, and Fig. 9 the balance of unexposed silver salts developed, the characteristic curve of the reversed picture is a mirror image of the original.
On this diagram there are three sets of curves for different times of development, but in each case the result is the same. We are, however, faced with one difficulty, and that is latitude. In the next slide are seen three sets of diagrammatic curves.
Figure | we willimagine to be thatof a perfect negative with a gamma of I, the shaded portion representing the original deposit. When this is dissolved away and the film re-developed, the unexposed silver salts blacken and we get a reversed picture indicated by the black portion. If we have a very steep curve and development proceeds too far we get reversal as is seen in Figure 2, an image—certainly equally steep—but obviously very much too poor in silver. On the other hand, if we do not develop sufficiently, and have a flat picture, as indicated in Figure 3, then on reversal we shall have too much silver to convert and the result will be too dense an image, as represented by the clear portion.
oe fanesce Rahts and Schutz have stated in a communication — to the VIIIth International Congress of Photography i that there is a latitude in exposure with Agfa plates of | Fig. 10 to 16. This takes into consideration the fact that these various faults we have just seen can be corrected by suitable treatment. A preliminary hypo bath before the second development will correct the undue amount of unexposed silver in Figure 3, while shortening development will correct the fault in Figure 2, but in commercial kinematography we have got to remember that hundreds of feet of film at a time, consist~ ing of various shots in the studio where lighting may constantly change both in character and intensity, necessitate flexibility of treatment, which is not in any way comparable with what can be given to an individual amateur plate. We -estimate that the latitude in taking a Spicer film is about 1 to 3 for over exposure and 1 to fin the case of under ; exposure. One might call thisa latitude of Fig. 11 1 to 9, but I prefer to callit a latitude of three times on either side of the correct exposure line. A further feature of the Spicer emulsion is the very small gelatine/silver ratio (only about 0-9 to 1), which has the
7
hog E
DEnxirx