تويت
تقييم التعرض والترشيح .. معالجة الألوان والطباعة .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Assessing exposure and filtration
The most important skill in color printing is controlling the tone and color of your result through exposure and color filtration . This is necessary for every image ; you are un- likely to find a negative which does not require some filtration . Differences in en- larger lamps , types of film , subject lighting , paper batches , and your subjective assess- ment of the image , mean that some color filtration is always necessary .
Additive and subtractive printing
You can control the color balance of your print either by subtractive ( " white light " ) printing or by additive ( " tri - color " ) printing .
In subtractive printing , pale yellow , mag- enta , and cyan filters are used to subtract some of the blue , green , and red from the light source . Additive printing uses three separate exposures through strong blue green , and red filters to control the color balance . Increasing the exposure through a
particular filter decreases this color in the print . Because three exposures are made for each print , additive printing is slow and shading and printing - in ( see p . 86 ) are difficult to do . Subtractive printing is much more convenient and therefore we shall be concentrating on this method .
Exposure and filtration tests
For each color negative you need to make two tests , the first for exposure and the second for filtration , as shown below . For the exposure test , you keep the filtration constant and then make several exposures of different times across a representative sec- tion of the image , rather like the black and white test strip ( see p . 80 ) . To assess the required filtration accurately , you should print the complete image each time using a different filtration , on a second test . You can do this by using a piece of black card , with one quarter cut out , laid over a whole
sheet of color paper . For each filtration , turn the card to expose a different quarter of the paper . The exposure time must be adjusted for each new filtration , as explained on page 169 .
Each filtration uses one or two of the filter colors only . Never filter all three colors at once . This creates “ neutral density " , lengthening the exposure time unneces- sarily , as explained on the opposite page . As a rough guide for the first filtration , if you have a Kodacolor II negative , use a 50Y 50M filtration . To remove a pre- dominant color cast in the print you must increase this color in the filtration . The " ring - around " guide on the opposite page shows the effects of adding different filters .
Always try to view your test strips and prints under a consistent light source to make your results as accurate as possible . A special " color matching " fluorescent tube or " daylight " lamp is ideal .
Making the exposure and filtration tests
1. Dial - in an estimated color filtration and compose and focus the image on the baseboard . In total darkness insert a strip of printing paper under the easel
2. With a piece of card make a series of exposure bands across the paper , giving increasing time to each band , e.g. 5 , 10 , and 20 seconds . Process the results as shown on page 168 .
3. From the exposure test strip estimate a likely filtration . In darkness place a whole sheet of paper under the easel and place the black card with one quarter cut away on top .
4. Give four exposures , using the card to uncover a new quarter of the paper . Each time alter the filtration ( and adjust the exposure time given by your first test accordingly ) . Process the print as shown on page 168 .
Analyzing the two tests
Exposure test
Judge the first test strip as you would a black and white print considering its darkness or light- ness and ignoring the color . In the best exposure band , in this case 20 seconds , there should be a good range of tones . Highlights should not appear bleached - out and the shadows should not be too dark The first test strip also gives you a guide to the required filtration .
Filtration test
Reading clockwise from the top left these prints were filtered at 50Y 50M , 50Y 55M , 55Y 55M , and 60Y 60M . The exposure times were 12 seconds , 12 seconds 14 seconds , and 17 seconds respec- tively . To remove a color cast you must add this color to the filtra- tion . Use the ring - around on the opposite page to help you decide on the changes in filtration .
Ring - around guide
A ring - around is a useful guide when color printing . The center print shows the best possible result from a typical negative . This is surrounded by prints which have been given different filtrations or exposures in regular amounts . Four of the six colors that can be produced by using the three com- plementary colored filters are shown magenta , cyan , yellow , and - green . To remove a cast from the print , you add filters which match that color . This means that to re- duce a primary color cast . you add the appropriate two com plementaries ( e.g. subtracting 10G from a print is achieved by adding 10Y and 10C filters .
Each filter affects one emulsion layer in the paper . For example , a yellow filter reduces the light affect- ing the blue sensitive layer , so that less yellow dye is formed in the print .
Neutral density
Sometimes after adding or sub- tracting filters you find yourself using all three filter colors together This lengthens the exposure time because of the gray ( neutral ) den- sity created by equal amounts of all three colors . The neutral den- sity can be removed by subtracting the lowest filter value from all three filtration values . For ex- ample , if you calculate a filtration of 60Y . 80M and 10C . you can simplify it to 50Y , 70M by sub- tracting 10 throughout . This gives the same color result but with a shorter exposure time .
Additive printing
Additive printing is cheaper than subtractive printing- you only need deep blue , green , and red gelatin filters . But because you have to use the three filters separately it takes three times as long as sub- tractive printing and shading and printing - in are impractical .
Before starting you should notch each filter so that you : can identify its color in the dark . The most useful test to make in additive printing is a " patch chart " , shown right , from which you can judge the correct exposure . This is made by using each of the filters in turn . First , with the blue filter under the lens , expose the whole image . Then change to the green filter and give a series of exposure times . left to right , across the print . Finally , using the red filter , give the same exposure series from top to bottom . Your processed test print will show nine variations .
Assessing the results
From this patch chart it can be seen that all three exposure times should be reduced by about one third to give a lighter result . The correct color here seems to lie in between the last two squares on the center row . The filtration chosen for the final print was 6 seconds through the blue filter , 20 seconds through the green filter and 29 seconds through the red filter .
Assessing exposure and filtration
The most important skill in color printing is controlling the tone and color of your result through exposure and color filtration . This is necessary for every image ; you are un- likely to find a negative which does not require some filtration . Differences in en- larger lamps , types of film , subject lighting , paper batches , and your subjective assess- ment of the image , mean that some color filtration is always necessary .
Additive and subtractive printing
You can control the color balance of your print either by subtractive ( " white light " ) printing or by additive ( " tri - color " ) printing .
In subtractive printing , pale yellow , mag- enta , and cyan filters are used to subtract some of the blue , green , and red from the light source . Additive printing uses three separate exposures through strong blue green , and red filters to control the color balance . Increasing the exposure through a
particular filter decreases this color in the print . Because three exposures are made for each print , additive printing is slow and shading and printing - in ( see p . 86 ) are difficult to do . Subtractive printing is much more convenient and therefore we shall be concentrating on this method .
Exposure and filtration tests
For each color negative you need to make two tests , the first for exposure and the second for filtration , as shown below . For the exposure test , you keep the filtration constant and then make several exposures of different times across a representative sec- tion of the image , rather like the black and white test strip ( see p . 80 ) . To assess the required filtration accurately , you should print the complete image each time using a different filtration , on a second test . You can do this by using a piece of black card , with one quarter cut out , laid over a whole
sheet of color paper . For each filtration , turn the card to expose a different quarter of the paper . The exposure time must be adjusted for each new filtration , as explained on page 169 .
Each filtration uses one or two of the filter colors only . Never filter all three colors at once . This creates “ neutral density " , lengthening the exposure time unneces- sarily , as explained on the opposite page . As a rough guide for the first filtration , if you have a Kodacolor II negative , use a 50Y 50M filtration . To remove a pre- dominant color cast in the print you must increase this color in the filtration . The " ring - around " guide on the opposite page shows the effects of adding different filters .
Always try to view your test strips and prints under a consistent light source to make your results as accurate as possible . A special " color matching " fluorescent tube or " daylight " lamp is ideal .
Making the exposure and filtration tests
1. Dial - in an estimated color filtration and compose and focus the image on the baseboard . In total darkness insert a strip of printing paper under the easel
2. With a piece of card make a series of exposure bands across the paper , giving increasing time to each band , e.g. 5 , 10 , and 20 seconds . Process the results as shown on page 168 .
3. From the exposure test strip estimate a likely filtration . In darkness place a whole sheet of paper under the easel and place the black card with one quarter cut away on top .
4. Give four exposures , using the card to uncover a new quarter of the paper . Each time alter the filtration ( and adjust the exposure time given by your first test accordingly ) . Process the print as shown on page 168 .
Analyzing the two tests
Exposure test
Judge the first test strip as you would a black and white print considering its darkness or light- ness and ignoring the color . In the best exposure band , in this case 20 seconds , there should be a good range of tones . Highlights should not appear bleached - out and the shadows should not be too dark The first test strip also gives you a guide to the required filtration .
Filtration test
Reading clockwise from the top left these prints were filtered at 50Y 50M , 50Y 55M , 55Y 55M , and 60Y 60M . The exposure times were 12 seconds , 12 seconds 14 seconds , and 17 seconds respec- tively . To remove a color cast you must add this color to the filtra- tion . Use the ring - around on the opposite page to help you decide on the changes in filtration .
Ring - around guide
A ring - around is a useful guide when color printing . The center print shows the best possible result from a typical negative . This is surrounded by prints which have been given different filtrations or exposures in regular amounts . Four of the six colors that can be produced by using the three com- plementary colored filters are shown magenta , cyan , yellow , and - green . To remove a cast from the print , you add filters which match that color . This means that to re- duce a primary color cast . you add the appropriate two com plementaries ( e.g. subtracting 10G from a print is achieved by adding 10Y and 10C filters .
Each filter affects one emulsion layer in the paper . For example , a yellow filter reduces the light affect- ing the blue sensitive layer , so that less yellow dye is formed in the print .
Neutral density
Sometimes after adding or sub- tracting filters you find yourself using all three filter colors together This lengthens the exposure time because of the gray ( neutral ) den- sity created by equal amounts of all three colors . The neutral den- sity can be removed by subtracting the lowest filter value from all three filtration values . For ex- ample , if you calculate a filtration of 60Y . 80M and 10C . you can simplify it to 50Y , 70M by sub- tracting 10 throughout . This gives the same color result but with a shorter exposure time .
Additive printing
Additive printing is cheaper than subtractive printing- you only need deep blue , green , and red gelatin filters . But because you have to use the three filters separately it takes three times as long as sub- tractive printing and shading and printing - in are impractical .
Before starting you should notch each filter so that you : can identify its color in the dark . The most useful test to make in additive printing is a " patch chart " , shown right , from which you can judge the correct exposure . This is made by using each of the filters in turn . First , with the blue filter under the lens , expose the whole image . Then change to the green filter and give a series of exposure times . left to right , across the print . Finally , using the red filter , give the same exposure series from top to bottom . Your processed test print will show nine variations .
Assessing the results
From this patch chart it can be seen that all three exposure times should be reduced by about one third to give a lighter result . The correct color here seems to lie in between the last two squares on the center row . The filtration chosen for the final print was 6 seconds through the blue filter , 20 seconds through the green filter and 29 seconds through the red filter .
تعليق