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التباين .. اختيار الفيلم .. كيفية التقاط وتطوير الصور بالأبيض والأسود
CONTRAST
The third related image quality is contrast . When used to describe the perfor- mance of a film , this is a measure of how the range of tones in the negative compares with the range of tones in the real scene . Although this is reasonably straightforward contrast is highly manipulable .
Imagine a typical daylit scene , with a full range of intermediate tones , some shadows and some highlights ( ignore the colours ) . With a meter , you could measure the range of tones ; there would probably be a difference of several stops between the lightest and darkest parts . A film that , given the correct exposure , reproduces all these tones more or less exactly has medium contrast . This , indeed , is what happens with a regular medium - speed film : if you take care over the exposure , processing , choice of paper grade , and printing , the final print should have the same tonal range .
However , contrast is linked to speed and graininess , and slow emulsions are more contrasty than fast . This is complicated a little by the processing stage : an extra - fine - grain developer , or under - development with any other , tends to lower contrast , while high - energy developers or over - development increase it .
Slow films tend to offer higher contrast , although using an extra - fine - grain developer tends to have the effect of lowering that contrast ( top ) .
These contrast differences affect the negative image but , unlike graininess which is transmitted faithfully from the negative to the print , the amount of contrast also depends on the printing stage . In practice , contrast differences between types of film and methods of development are much less than those that can be made later , in the darkroom . As we will see in the section on printing , the selection of printing paper grade , dodging and burning - in tech- niques and print development can cover most of the film differences .
If you examine a negative carefully with a magnifier , and then a straight- forward print is made from it , you will notice that there is more highlight and shadow detail recorded in the negative than in the print . This is because the volume of the transparent gelatin in which the grains are embedded prevents absolute blackness , while in the unexposed areas gelatin and film base together give a pale grey tone . A print , on the other hand , is viewed by reflected light , so that the black silver grains that form the shadow areas have a double effect ( they block light falling on the paper and that reflected from it ) . The high- lights in a print can be as bright as the coating , which is deliberately chosen for its whiteness .
Note how there is more shadow and highlight detail in the negative ( below ) than in the straightforward print produced from it ( above ) .
CONTRAST
The third related image quality is contrast . When used to describe the perfor- mance of a film , this is a measure of how the range of tones in the negative compares with the range of tones in the real scene . Although this is reasonably straightforward contrast is highly manipulable .
Imagine a typical daylit scene , with a full range of intermediate tones , some shadows and some highlights ( ignore the colours ) . With a meter , you could measure the range of tones ; there would probably be a difference of several stops between the lightest and darkest parts . A film that , given the correct exposure , reproduces all these tones more or less exactly has medium contrast . This , indeed , is what happens with a regular medium - speed film : if you take care over the exposure , processing , choice of paper grade , and printing , the final print should have the same tonal range .
However , contrast is linked to speed and graininess , and slow emulsions are more contrasty than fast . This is complicated a little by the processing stage : an extra - fine - grain developer , or under - development with any other , tends to lower contrast , while high - energy developers or over - development increase it .
Slow films tend to offer higher contrast , although using an extra - fine - grain developer tends to have the effect of lowering that contrast ( top ) .
These contrast differences affect the negative image but , unlike graininess which is transmitted faithfully from the negative to the print , the amount of contrast also depends on the printing stage . In practice , contrast differences between types of film and methods of development are much less than those that can be made later , in the darkroom . As we will see in the section on printing , the selection of printing paper grade , dodging and burning - in tech- niques and print development can cover most of the film differences .
If you examine a negative carefully with a magnifier , and then a straight- forward print is made from it , you will notice that there is more highlight and shadow detail recorded in the negative than in the print . This is because the volume of the transparent gelatin in which the grains are embedded prevents absolute blackness , while in the unexposed areas gelatin and film base together give a pale grey tone . A print , on the other hand , is viewed by reflected light , so that the black silver grains that form the shadow areas have a double effect ( they block light falling on the paper and that reflected from it ) . The high- lights in a print can be as bright as the coating , which is deliberately chosen for its whiteness .
Note how there is more shadow and highlight detail in the negative ( below ) than in the straightforward print produced from it ( above ) .
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