طرق طبع الصور الملونة - ٢ - كيف تعالج الصور .. كتاب التصوير الضوئي

Methods of printing color photos - 2 - How to process photos .. Photography book

- Using a mosaic filter

It is based on the principle that most images contain at least an area composed of a group of colors whose mixture gives a neutral gray surface.

The mosaic filter consists of adjacent colored surfaces, each of which represents a group of filters. For use, the experiment is achieved through the mosaic after the magnifier is calibrated. A bath is placed under the lens to enlarge the image. After processing, the surface of the experiment should appear gray. Refer to the method of use to determine which of the filter groups to use and how to calculate the exposure for the final image.

- Mosaic filter method: It consists of a mosaic piece made of transparent colored surfaces, a bath, and a gray color scale.

- Using a color analyzer:
It is an electronic device that measures the proportions of the primary colors (red - green - blue) contained in a white light source. These values ​​allow the negative to be compared with standard negatives that have been properly enlarged and their values ​​help to measure the analyzer. The differences in values ​​are expressed in the values ​​of the filters that must be entered to obtain a well-balanced image without overwhelming color.

Amateur color analyzers usually read the entire area of ​​the negative because their measuring device is mounted directly under the magnifying lens. Professional color analyzers are equipped with a small measuring device that allows the selection of the desired surface measurement in the image being analyzed.

- Addition method:

This is the method that can be followed if you only want to make a few enlargements during each session: the tools used are simpler and we can use an enlargement without a filter drawer. A set of three saturated filters called trichromatic filters - red, blue and green - and a filter holder are required to be placed under the lens during the exposure.

The realization of the image requires printing each of the three layers of paper in succession, each layer separately, by changing the filter for each exposure. The duration of each print must correspond to a complete balance of the color densities in each of the three layers. We obtain these exposure durations either by the method indicated below or by using a mosaic filter. It is very important to prevent any movement of the negatives and the sensitive paper during all operations: also be careful not to move the enlarger while changing the filters.

- Addition principle: The colors blue, green and red are called the primary or primary colors of white light. Because these three colors are! The problem is that the first color filters absorb two-thirds of the visible spectrum, leaving only a third: their own color.

- Magnifiers: Magnifiers: The complexity of the magnifiers for adding-pull magnification varies from one device to another.

Sometimes we make three exposures through three-color filters.

Sometimes we use three separate light sources, green, red and blue.

Magnifiers with a filter tray are used for adding-pull. Place the filters in this tray.

- Conducting experiments:
Either by tactile search or by mosaic.
For the first method: In the dark, with the sensitive paper in place, pass the blue filter through the tray and make a general exposure of 10 seconds: this forms the yellow image. Replace the blue filter with the green filter. Under this filter, make successive exposures of 10 - 15 - 20 - 25 seconds, moving the piece of cardboard horizontally to hide. Do the same with the red filter, but move the piece of cardboard vertically. The first experiment can be like the image above on the left: very light, lacking yellow.

To get yellow, make a second experiment with the same exposure times for green and red, but increase the exposure time for blue. When the experiment contains a square with satisfactory colors and intensity, achieve the final image using the three appropriate exposure times.

15 seconds under blue filter
10 seconds under blue filter
15 seconds under blue filter
20 seconds under blue filter