Suggestions for the Improvement of Illustrations

Abstract

Photo-engraving is an art of reproduction. Excellence is reached when a perfect reproduction of the original copy is achieved. Since photography is the basis of photo-engraving, the copy used for the purpose of illustration is most important. The illustrations used in Radiology are printed from photo-engravings that come under two classifications—line engravings made from charts, graphs, and pen-and-ink drawings, and halftones made from photographs and x-ray photoprints, etc. The copy for both line cuts and halftones may be enlarged to about double the size of the copy and may be reduced to one-sixth the original size of the copy. However, extreme reductions usually lose much of the detail, while enlargements magnify any imperfections there may be in the original. The copy for line cuts must have dense black lines on white stock and the detail must be sufficiently clear so that it will not be lost when reductions are made. If charts or graphs are photographed, the photographic print, used by the engraver as copy, should be made so that all lines are a dense black, even though the white background be slightly clouded. This is preferable to having a clear white background and gray lines. If the above suggestions for line cuts are followed, the engraver will have no difficulty in the reproduction of clear and readable charts and graphs. Halftones are made by photographing the copy through a screen which breaks the continued tones of the photographs into dots of various sizes which can readily be seen by looking at a halftone with a magnifying glass. Breaking the tones into dot formation causes the loss of some detail, which is noticeable even when the copy is reproduced same size. Therefore, wherever possible, unnecessary parts of the copy should be eliminated so that the essential part of the photograph will not require greater reduction than is absolutely necessary. There are three classifications of dot formations which are found on every halftone engraving, namely, the high-light dot which is the lightest tone of the copy; the middle tones which include the light and darker grays, and the shadow dot which is the blacker tones. (You will notice by looking at any halftone reproduction the different size of dots in the various tones.) To make a satisfactory etching of a halftone it is etched in the following steps: The plate is given a flat etch to a printing depth. The shadows are then held back by being painted in with an acid resist and the etching continues, giving a tone separation between the shadows and middle tones. After the middle tones have been sufficiently lightened these tones are held back and the high-lights etched lighter. By this separation various tones can be brought out by re-etching.