How to calculate and modify the exposure time during the color correction process?
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To calculate and modify the exposure time according to the sample, you must first know the three factors that cause the exposure time to change during the color correction process (ie, the density of the color filter, the number of sheets, and the density of the sample). Change the value and then calculate the new exposure time based on these values.
(1) Effect of color filter density change on exposure time Generally, magenta and cyan filter have the same effect on exposure, and the exposure time needs to be increased or decreased by 10% for each increase or decrease of 10 densities. The yellow filter has a small effect on the exposure, and the exposure time differs by only 10% when the difference is 40 densities. The following two tables are calculated by calculation for reference when calculating the exposure time. Effect of density change of magenta and cyan filter on exposure time
(2) Effect of the change of the number of sheets on the exposure time Generally, the transmittance of the new filter is good, and each filter has a difference of 10%. If the color filter is worn out, the surface is rubbed, and the light transmittance is lowered, each filter has a difference of 15% or more of the exposure time. Effect of the change of the number of filters on the exposure time
(3) Effect of sample density on exposure time If the exposure time is too much or insufficient, the exposure time should be calculated according to the data in the table according to the amount of excess or deficiency (percentage). Sample density (dark) modification of exposure time
Here are two examples to illustrate the calculation method for modifying the sample exposure.
Example 1: The original sample filter combination is 60 40 00.
Exposure time: 10 seconds
Number of color filters: 2 sheets
After the sample is judged to be magenta, it is estimated that 20 density magenta filters should be added. The sample density is low and it is estimated to increase the exposure by 10%.
Therefore, the modified color filter combination is 60 60 00
Check the table to know that adding 20 density magenta should be × 1.2
The number of filters has not changed.
Look up the table, the density is 10% smaller ×1.1
Therefore, the exposure time after the change is: 10 (seconds) × 1.2 × 1.1 = 13.2 (seconds)
Example 2: The original sample filter combination is 40 30 00
Exposure time: 15 seconds
Number of color filters: 2 sheets
After the sample was judged: the color was yellowish 30 densities, 15 densities were green, and the sample was 20% lighter.
Therefore, the modified combination of the color filters is: 40 30 00 +30 00 15 70 30 15 -15 15 15 55 15 00
The revised changes are:
Yellow filter adds 15 densities × 1.05
Magenta filter reduces 15 densities × 0.85
Add two color filters × 1.2
Then the exposure time should be modified:
15 (seconds) × 1.05 × 0.85 × 1.2 = 16 (seconds)