The Film Renter and Moving Picture News (Mar-Apr 1923)

March 17, 1923 THE FILM RENTER & MOVING PICTURE NEWS. (Technical Supplement). 85 PLEA FOR A STANDARD DENSITY IN FILM PRINTING. American Expert writes on much discussed subject, and gives many useful tips. (By Dr. WILLIAM E. STOREY, of the Society of Motion Picture Engineers of America) 7 HE motion-picture industry has perhaps the least excuse L of any branch of applied science for not obtaining and using satisfactory standards. There is no engineering line, except perhaps railroading, in which the same elaborate and accurately cut product passes through as many different and independent processes as does the motion-picture film; and often no two of these processes are controlled by the same concern. Not only is the film manufactured by one company, taken by another, developed and printed by a third and used by a fourth, but the theatres can use any one film but a short time to advantage. Accordingly, a circulating system is essential. This, again, is the strongest of reasons for having the film interchangeable, It is to be regretted that the dimensions adopted in America do not agree exactly with those of the English as adopted by the Incorporated Association of Kinematograph Manufacturers, though both standards can be run on the same machine. At present, then, there is ‘thorough co-operation between the various branches of the industry with respect to the size of the film used. There are two other factors, however, that if not as necessary of standardisation, should not be left out of consideration entirely. These two things are average density of negative, and contrast, and it is the investigation of these two properties of the film in which we are at present particularly interested. Our Present Method. I believe it is now the universal custom to make a number of prints of different densities from each negative film, and from the examination. of these to choose the time of exposure of tha final print. To one unfamiliar with the technique of printing, this method would seem to have objections. It is obviously impossible that the judging be carried on under the same conditions as those under which the film will be used, since theatres differ so much in the screen and auditorium illumination, in the size and distance of the picture and in many other ways that will affect the appearance of the screen. Apart from any difference of opinion among the judges, an allowance must be made for the different conditions obtaining in the final projection. I have it on good authority that sometimes eight times the intensity of illuminaion is used for judging as is found on the average theatre screen. I know that many prints are judged by holding them up to the sky or in front of a screen illuminated by daylight. Such surroundings and illumination will change so much during a few hours, or even minutes, as to cause serious doubt as to the reproducibility of results obtained by such methods, In any event it would seem quite impossible to make sufficient allowance for such ‘‘ abnormal '’ methods of viewing a film. Need of Specific Values. The only obviously accurate way of determining that density of film that ‘‘ looks ’’ the best is to decide, first of all, upon some specific value of the various factors that go to determine the appearance of a picture in a theatre. The average values of these factors as found at present might be selected as standard, or some arbitrary values might be chsoen, with the expectation of the theatre gradually conforming to these standards or making allowance for the departure they find necessary. Prints selected under these conditions would represent, apart from individual judgment, the proper printing of the negative in question for a theatre complying with the standards selected. There are, of course, great objections to this method of judging films, Apart from the trouble and time required, a theatre is necessary. Again, the length of film. that must be printed to each density for trial is considerably greater than at present, and perhaps the difficulty of comparing different trials, run successively as they, wauld probably be, might be great. What is the Gain? These are doubtless some of the dificulties that have prevented, the adoption of standards in printing. And to balance all this trouble and expense, what is the gain—an added ease in the determination of the amperage necessary for projection, with a little lower allowance for the over-dense film; slightly more assurance against the. flaring out of the thin film; a little more uniformly successful picture. The one absolute essential for a print is that detail necessary for the understanding of the. picture must be present on the screen. Obviously this detail cannot appear on the screen unless. corresponding detail exists in a positive film. | Sufficient Contrast. Needed. Now detail exists in a picture only through contrast, and, in the case of monochromes, through density contract. It is true that detail depends also on contrast gradient, that is, on the width of the strip through which one density fades into another, as well as upon the difference in the two densities. The width of this strip depends, however, on the sharpness of the negative. With this the present discussion has nothing te do; it deals simply with the printing of a given negative. The first step in the solution of the problem is, then, to have sufficient contrast in the necessary parts of the picture. By ‘* necessary ’’ is meant those parts necessary for the understanding of the picture. Characteristics of Positive. Whether or not the contrast will be sufficient, will depend, apart from the contrast of the negative, on the slope of the characteristic curve of the positive film. Since this slope is a maximum at one point and but slightly less than this through a considerable range (the so-called ‘‘ region of correct expo sure '’), falling off then more rapidly to zero for exposures below and above this region, the positive must for maximum contrast be printed such a length of time that every part of interest has an exposure in or near this region. If there is sufficient contrast in a particular area of the negative, the time of printing may depart considerably from that of the region of correct exposure for this area. If there is but slight contrast, then any under or over-exposure may lessen the contrast beyond the limit of eye sensitivity. If the contrast in the negative is too low, satisfactory detail will be impossible for any exposure, unless in some way the slope of the characteristic curve can be increased.