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تحويل الألوان إلى درجات - ٢ - الصورة أحادية اللون .. كيفية التقاط وتطوير الصور بالأبيض والأسود
COLOURS INTO TONES
These are the two major differences in sensitivity to colour between film and the human eye , and as the eye is the final arbiter , the uncorrected photo- graphic version may look unnatural . How important , or even how noticeable , this is depends on the familiarity of the scene . For instance , it is not likely to matter whether a red telephone looks almost black in a photograph - for all that the viewer knows , it might well be black . A tomato , however , is a different matter , as is red lipstick : we expect these to be a certain tone . Equally , we think of a blue sky as having a substantial tone , that ought in black - and - white to be a shade of grey something between medium and medium - pale . However , an uncorrected shot that includes the sky will show it as almost white because film is over - sensitive to this colour .
The principle of using coloured filters to control the tone is quite straight- forward . Whatever the colour of the filter , it will pass its own wavelength but block out the remainder . As an example , a strong red filter , such as a Wratten 25 , will allow the red components of light through , but hold back most of the blues and greens ; this is something you can check just by holding it to your eye . Now , most scenes , and certainly most natural ones , are made up of combina- tions of colours , and there are surprisingly few pure , unadulterated hues . For most of a picture , therefore , this red filter will make only small differences . The red telephone mentioned above , however , will look very pale indeed - almost white - while anything green will appear virtually black . The rule is : use a filter of the same hue if you want to lighten the tone of a colour , but use a filter of a complementary hue to darken it . Complementary colours are the opposites ; if mixed , they would cancel each other out . Place a red filter over a green one , for instance , and the result will be neutral and almost opaque .
The best - known tone control in black - and - white photography is to darken a blue sky , and for this a yellow , orange or even red filter is used . A yellow filter gives an approximately normal rendering - to the eye , that is . The reasons for darkening the sky are only partly to do with film's over - sensitivity to blue ; in a typical landscape composition , a pale and featureless sky lets the attention drift off towards the top . A darker tone above often helps to pull the eye back down into the frame .
The strength of the filter's effect depends not only on the density of the filter , but also on the colour purity in the subject . Blue sky is strongly affected , but many colours in nature give disappointing results . For example , you might expect a green filter to make vegetation appear quite pale . In practice , particu- larly with overall views of trees , the effect is weak , because most such greens are in fact degraded with browns yellows , and other colours .
In addition to using filtration to correct tonal values , it can also be used to manipulate them to suit your own tastes . Green and red of about the same intensity are immediately different in a coloured view ( they are almost op- posites ) , but in monochrome they may look very similar , and juxtaposed be difficult to tell apart . Using a filter of either colour will increase tonal separa- tion .
As a filter passes less light through to the film , the exposure usually needs to be increased . The best guide to this is the filter factor ; do not always rely on the camera's through - the - lens meter , as this has a colour sensitivity that is rather different to that of the eye .
The best , and by far the simplest , way of appreciating the dramatic changes that can be made to a black and white photo is to put theory to the test . Compare the sky in the unfiltered picture ( top ) with the lacklustre sky in the picture taken using a blue filter ( second from top Then note how using a yellow filter ( second from above ) has restored the blue to an acceptable strength . Finally , compare the unfiltered picture with the red filtered shot ( above ) ; the extremely dark sky produced by using a red filter may not be to everybody's taste .
No filter
Blue filter
Red filter
Yellow filter
Filter Checklist for Black - and - White Film
All the filters below , except the polarizer , are available in either glass or gelatin . As the glass thickness can distort , high optical quality is important in a filter , and this is expensive . Gelatin filters , on the other hand , are too thin to affect the optics of a lens , but must be handled carefully to avoid marking .
* This list of filter factors and the related increase in aperture is based on normal daylight . When the colour temperature changes , in the evening , for instance , these factors will change .
Coloured filters provide the necessary contrast control in black - and - white photography . The tomato appears light on the left - hand side of the picture , because a red filter was used . Compare this with the opposite side of the picture , where it is the lettuce which is lighter , the result of a green filter being used .
ABOVE A red filter holds back green
ABOVE A green filter , being the complementary of red , passes green but blocks red .
COLOURS INTO TONES
These are the two major differences in sensitivity to colour between film and the human eye , and as the eye is the final arbiter , the uncorrected photo- graphic version may look unnatural . How important , or even how noticeable , this is depends on the familiarity of the scene . For instance , it is not likely to matter whether a red telephone looks almost black in a photograph - for all that the viewer knows , it might well be black . A tomato , however , is a different matter , as is red lipstick : we expect these to be a certain tone . Equally , we think of a blue sky as having a substantial tone , that ought in black - and - white to be a shade of grey something between medium and medium - pale . However , an uncorrected shot that includes the sky will show it as almost white because film is over - sensitive to this colour .
The principle of using coloured filters to control the tone is quite straight- forward . Whatever the colour of the filter , it will pass its own wavelength but block out the remainder . As an example , a strong red filter , such as a Wratten 25 , will allow the red components of light through , but hold back most of the blues and greens ; this is something you can check just by holding it to your eye . Now , most scenes , and certainly most natural ones , are made up of combina- tions of colours , and there are surprisingly few pure , unadulterated hues . For most of a picture , therefore , this red filter will make only small differences . The red telephone mentioned above , however , will look very pale indeed - almost white - while anything green will appear virtually black . The rule is : use a filter of the same hue if you want to lighten the tone of a colour , but use a filter of a complementary hue to darken it . Complementary colours are the opposites ; if mixed , they would cancel each other out . Place a red filter over a green one , for instance , and the result will be neutral and almost opaque .
The best - known tone control in black - and - white photography is to darken a blue sky , and for this a yellow , orange or even red filter is used . A yellow filter gives an approximately normal rendering - to the eye , that is . The reasons for darkening the sky are only partly to do with film's over - sensitivity to blue ; in a typical landscape composition , a pale and featureless sky lets the attention drift off towards the top . A darker tone above often helps to pull the eye back down into the frame .
The strength of the filter's effect depends not only on the density of the filter , but also on the colour purity in the subject . Blue sky is strongly affected , but many colours in nature give disappointing results . For example , you might expect a green filter to make vegetation appear quite pale . In practice , particu- larly with overall views of trees , the effect is weak , because most such greens are in fact degraded with browns yellows , and other colours .
In addition to using filtration to correct tonal values , it can also be used to manipulate them to suit your own tastes . Green and red of about the same intensity are immediately different in a coloured view ( they are almost op- posites ) , but in monochrome they may look very similar , and juxtaposed be difficult to tell apart . Using a filter of either colour will increase tonal separa- tion .
As a filter passes less light through to the film , the exposure usually needs to be increased . The best guide to this is the filter factor ; do not always rely on the camera's through - the - lens meter , as this has a colour sensitivity that is rather different to that of the eye .
The best , and by far the simplest , way of appreciating the dramatic changes that can be made to a black and white photo is to put theory to the test . Compare the sky in the unfiltered picture ( top ) with the lacklustre sky in the picture taken using a blue filter ( second from top Then note how using a yellow filter ( second from above ) has restored the blue to an acceptable strength . Finally , compare the unfiltered picture with the red filtered shot ( above ) ; the extremely dark sky produced by using a red filter may not be to everybody's taste .
No filter
Blue filter
Red filter
Yellow filter
Filter Checklist for Black - and - White Film
All the filters below , except the polarizer , are available in either glass or gelatin . As the glass thickness can distort , high optical quality is important in a filter , and this is expensive . Gelatin filters , on the other hand , are too thin to affect the optics of a lens , but must be handled carefully to avoid marking .
* This list of filter factors and the related increase in aperture is based on normal daylight . When the colour temperature changes , in the evening , for instance , these factors will change .
Coloured filters provide the necessary contrast control in black - and - white photography . The tomato appears light on the left - hand side of the picture , because a red filter was used . Compare this with the opposite side of the picture , where it is the lettuce which is lighter , the result of a green filter being used .
ABOVE A red filter holds back green
ABOVE A green filter , being the complementary of red , passes green but blocks red .
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