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Color correction of color positive images by addition

The additive correction method

This method differs - to some extent - from the previous one, which was explained on p. 306, in which we rely on correcting the colors of the image by means of subtractive correction. In addition correction, sensitive paper is exposed to different colors of light rays. Or the light source may be one and project the photosensitive paper three consecutive times, each through one of the three filters placed in front of the lens (Fig. 72). One of these filters is red (such as the Wratten No. 70 filter), the second filter is green (such as the Wrattend No. 99), and the third is blue. (Example Candidate 98.rattan No.)

Since correcting the colors of the images by addition requires that we control the amount of light that the sensitive paper receives from each of the colors of the light rays that pass through the filters, so two methods are used to perform this purpose:

(a) Either by controlling the duration of exposing the paper to each of the colors of the rays passing through the three filters, which is the method that is usually followed (2).

Since these filters do not allow ultraviolet rays to permeate them, it is therefore possible to dispense with the filter 23 that absorbs these rays and is usually placed in the lighting house.

(1) That is, their colors represent the primary colors, in contrast to the correction by deletion, in which filters representing the complementary colors (yellow - scarlet - cyan) are used. And she

(2) The following translator mentions: Jack H. Coote. Color Prints Revised edition (1963) p.182. In this case, the ratio between the three exposures through the filters would be four seconds for the red filter, 7 seconds for the green filter, and 14 seconds for the blue filter, if we used the three filters mentioned abov- The order of exposure priority through the three filters has no importance, so it is permissible to start first with the blue exposure and then with the other two exposures, and it is also permissible to start with the red exposure first and then the others, or with the green exposure first and so on. However, it is much better if he follows a certain order that we stay in that order. (b) Or by controlling the intensity of the light emitted by each of the three light sources, if we use three colored light sources. Perhaps it is indispensable to mention that any magnifier used to prepare black and white images will be suitable for preparing color images with correction (by addition), provided that one or another means of placing filters is prepared in front of the lens (Fig. 72, 73). Also, there is no difference in the type of color-sensitive papers used in the case of color correction by deletion (which we have already talked about on p. 297). Integral multi-layer color materials are the same used in both cases. Colors

(fig. 72)

One way to place filters is in front of the magnifier lens

Fix colors by adding

Additive correction (1) one of the three filters (b) the carrying disk the three filters (h) the magnifying glass.

It is worth noting that it is suitable for any usual magnifier used for “black and white” images to work in enlarging color images with color correction by way

add .

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(Fig. 73) Another way to perform the above hypothesis

bar from the airport

Twisted wire load filters

The three filters