DEPTH IN FILMS

Evening Post, Issue 73, 23 September 1936, Page 19

DEPTH IN FILMS

FRENCH EXPERIMENTS

IMPRESSION OF DISTANCE

PROGRESS OF WORK

Have you ever wondered why you get the impression exf distance when you look at an object? asks Louis Polleticr in "Marianne," Paris. This is why, he says: Little by little, since your birth or at least since your eyes became tive to light, you have been familiar with the third dimension of distance. Slowly, by a process which is hard to explain, and isn't even fully understood, in which the differences between light and shade certainly played an important part, you acquired experimentally the ideas that make up the laws of linear perspective. But getting the idea of relief was made much easier for you by the fact that the two pictures of an object that form on the retinas of your two eyes are slightly different. They are registered, as photographers would say, on two different cameras. Now come over into photography itself, and take [ two pictures in two cameras, side by side, and as far apart as the normal eyes, which is about 2.7 inches. While ordinary modern movie films carry one series of pictures, run off at a certain speed (from sixteen to twenty a second), the stereoscopic films of the future will carry two series of pictures, running parallel to each other, one corresponding to the right eye and the other to the left eye. As in present 'films, the strip for sound effects will be beside the picture part of the film. NO GREAT DIFFICULTIES. So far the problem of three-dimen-sional films has not offered any great difficulties. Many years ago, less than fifteen years after the discovery of photography by Nicephore Niepce of Chalon, the French physician Rolman thought of the stereoscopic picture that Almeida discovered independently in 1858. These pictures were made in two complementary colours, colours, that is, that make white when added together, like red and green. Two simple experiments will make thjs point clear. Make a sketch on white paper in green, ink. If you look at it through a, glass coloured a darker green, you won't see the sketch at all. But look at it through a red glass and the sketch will appear black, -on a red background. Why? Because the red glass absorbs tlie green light rays given off from the lines of the sketch and keeps them from reaching your retina. Now make another sketch on white paper, this time in red ink. Look at it through glass coloured a darker red and you won't see the sketch at all, but through green glass it will look black and a green background. Think of it ,this way: imagine that the picture seen in green is seen by the left eye, and.the one in red by the right eye; what happens when they are seen at the same time? If you tried it by making spectacles with the left lens green and the right lens red, according to what has just been said, the left eye will not see the image that the. right eye does, and the right eye will not see the one the left eye sees. Each' retina will register only its own picture, and the observer will get a sharp impression of relief, of depth, in the picture. METHOD TOO COSTLY. But this method costs too much: in a short time the eyes will become very tired and strained, because they are not receiving the same amount of light, and the nervous system cannot blend the two images together for any length of time. That is the basic problem that Louis Lumiere tackled in his work on the three-dimensional film. The principle of his method lies in the explanation of certain points that demand a good knowledge of biological physics. In the first stage of experiment, the observer has a pair of spectacles the glasses of which have been chemically treated with the greatest possible respect for the laws of the eyes' sensitivity; it is possible to Watch a performance through these glasses for some hours without tiring the eyes. That the desired result can be obtained is proved when you see the films already made by Lumiere's process. Among them are a section of the Mediterranean beach, where the bathers look very much alive; two elephants photographed close up with the result that their trunks seem to wave out from the screen; the train coming into La Ciotat where Lumiere cranked off his first Him forty years ago; a flight of pigeons that seemed to swoop through the hall; and a ladder that looks as if it Were falling right on to the, audience. . The technique of making these pictures requires the: use of a series of lines, or grilles, on the. film, so that the surface is composed of parallel opaque lines with transparent spaces between them. In the method now being used the width of the opaque lines is slightly greater than that of the open spaces. HOW THE PROCESS WORKS. To understand . how this process works take, an ordinary stereoscopic scene made up of the two necessary pictures, the left picture for the left eye and the right one for the right eye, and break up these two pictures into fine parallel bands by following the lines that go from top to bottom of each picture. If, after numbering the bands of the picture on the left in the natural order, 1, 2, 3, 4, 5, 6, ... you take out the even numbers, 2, 4, 6 . . . you. will have an incomplete picture left, because every other band will be missing. But if the bands are fine enough their absence will not spoil the whole effect of the picture. That is the way photo-engravings are made, of course, and while they look continuous and smooth from a distance they are really made up of very small points of colour. Now, do the same thing with the right-hand picture, and after numbering the bands in the same way, take out the odd numbered bands, 1, 3, 5. ... In this way we get two pictures of a stereoscopic pair, both incomplete, but each, when looked at through a stereoscope, giving an acceptable impression. From the two half-pictures we now have, composed of' the odd bands of the left and the even bands of the right picture, make only one plate, which we will call the composite picture, with all the bands in their proper numerical order, running 1, 2, 3, 4, 5, 6. Thus we have a composite picture made up of two incomplete pictures, each one made of thread-like bands, and the bands of the composite picture coming alternately from each half-picture. THE FINAL PROJECTION. So we have the two pictures in the one plate, but so arranged that we can sort them out again automatically and make one eye see one picture to the exclusion of the other by the use of coloured spectacles. The principle of the technique is not hard to understand. But putting it into practice! . You can easily see that that's another matter. ' First the automatic stereoscopic film will be lined oa one side, andl covered on the