Write a note on Print Variations
Variation in print of photographs is caused by a number of factors which are: material, surface, weight, contrast, and tone. These are discussed as:
Prints are of three types:
- Opaque paper prints
Paper prints are the cheapest, and they are commonly used for routine photo-interpretation.
- Cronapaque prints
Cronapaque prints are intermediate in quality b/w paper prints and diapositives.
- Film positives transparencies (diapositives)
Diapositives prints on glass are characterized by the least dimensional changes and the sharpest detail.
Positive prints from photographic negatives may be printed on transparent translucent or on opaque media. Positive film transparencies are comparatively costly, but they are superior to opaque prints for photo-interpretation.
The print surface and character of photographic papers are some of the important considerations in obtaining and handling aerial photographs. So far as prints surface are concerned, they are of three types:
- Glossy Prints:
The word “glossy” means smooth and shiny. In photo-interpretation, it means smooth luster. These prints produce the sharpest detail, but they reflect glare and are difficult to write upon, develop cracks with excessive handling and are not suited to necessary bending under the lens stereoscope.
- Semi-matte Prints:
“Semi” means half and “matte” means dull finish which together means “neither very shiny nor very dull and coarse.” These prints are desirable because they have a minimum glare, and the surface is not too smooth to mark or write upon.
- Matte Dried Glossy:
These are preferable because they combine the good qualities of glossy a semi-matte prints.
The prints are smooth and shiny yet the glare is not offensive. The surface is sufficiently toothed to be easily marked yet the prints retain high-resolution quality and sufficient contrast. These prints are made on paper, but they retain dimensional stability.
On the basis of weight, photo prints are classified into two main categories:
- Single Weight Prints:
In this case, photo prints are obtained on single weight paper. The prints are less expensive and are much easier to handle under the pocket stereoscope and are flexible. They also take less storage space. They are, however, subject to curling and dimensional changes caused by variations in temperature and humidity.
- Double Weight Prints:
The prints obtained on double weight papers are stiffer, more durable and less susceptible to dimensional changes caused by variations in temperature and humidity. They are, however, heavy and require more storage capacity.
Contrast refers to the degree of differentiation b/w the tones. Photographs with very dark and very light tones have generally high contrast. (See the pic _ from left: Nazir Jan, Asif, Saleem Javid, Mubbashir, Imran Sb, Kamran, Yar Jan, and Imran Ameer Sb)
The amount of contrast is determined by light reflections of objects, clearness of atmosphere, and photographic techniques, like:
- Atmosphere haze scatters light and reduces contrast.
- Photographs taken on bright days have greater contrast than those taken on dull days.
- Soil when wet absorbs light, and therefore, the photographs are darker than the dry soil photographs.
Contrast changes from season to season, from place to place, and it can be increased or decreased by the exposure time or the time for developing film and by the paper used for making prints.
Each distinguishable shade from black to white is called tone. The tone of an image depends upon the amount of light reflected by the object. The amount of light reflected depends upon:
- Nature and the colors of the surface of the object.
- The degree to which the object is exposed to the Sun.
- The angle of reflection from the object to the camera.
On all above basis:
- Smooth roads, dry soil, etc. appears white from a wide range because of reflection of light.
- Forest vegetation, wet soil, and water bodies register grey to dark tone on aerial photographs because these absorb light.
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