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Colour photography or the colour method .. How to process pictures .. The book of photography

How to process pictures
Colour photography or the colour method

Commercial colour photography has been around since 1907 but the early principles are nothing like those of today. The decisive turning point came in 1935 when the reversible film with overlapping layers called (Tripak) was introduced. This film was very easy to use. The clarity of the image and the stability and quality of the colours made it a success and its processing was always guaranteed by the manufacturer.

Since then a whole range of films has been brought to the market, some of these materials are complete devices in themselves (see pages 223-222) but most require laboratory processing to produce either printed images on sensitive paper or positive images for display (slides).

The variety of films available today is interesting: from the fine-grained 16 ASA to the very fast 500 ASA, most films have a speed between 50 ASA and 100 ASA. There are several types of color films because they cannot adapt, as the human eye does, to different types of light: a film will only give correct colors if it is exposed to light with a very specific spectral characteristic. There is the "daylight" type (5400 k) and the "artificial light" types (3200 or 3400 k). The vast range of possibilities offered by color film is shown in the figure below: it shows that there is more than one way to achieve the desired result.

In general, the final quality is better when there are only a minimum of intermediate stages. With the exception of instant photography, which gives the image directly, the flexibility of the color principle is shown in the following: for example, if you take a color negative film in order to print images on sensitive paper, you can obtain positive images for display, but they are less advantageous than those taken directly on reversible film, for the simple reason that an additional stage is required. (By reversible film, we mean positive film.)

When choosing a type and principle, pay attention to what each one specifies. For example, it seems that taking pictures on reversible film and then printing images on reversible paper is a good principle, but the exposure of the film must be very precise, while with the negative/positive principle we can allow ourselves without any risk of a slight error in exposure that can be corrected in printing. Tri-Pac Color Film:

The film has three light-sensitive layers: the top layer is sensitive to blue, the middle to green and the bottom to red. A yellow filter eliminates during processing (see its position in the drawing) the intrusive blue in the middle and bottom layers which are slightly sensitive to blue.

- Production of color images:

- Second copies of positive images or slides: We use a film that can be pulled into second copies with soft life and low contrast. The second copy is often more contrast than the original: The exposure must be very correct.

- Positive images or slides: A wide variety of films from 12 ASA to 500 ASA. Some can be pushed during development from 2 to 3 holes in the lens. Correct exposure.

Images on reversible paper The original positive image must be well exposed. Some papers have a reversal stage during processing. A filter is placed on the images during enlargement.

Negative/Positive Photographs:

Negative photographs that have been overexposed by one value of the diaphragm opening can still be drawn. The color saturation increases with the increase in exposure and vice versa, it is necessary to place the filter during the enlargement.

Negative/Positive Photographs:
As mentioned above, sometimes with increased contrast.

Instant color photograph:
It requires a special photographic machine. The image appears automatically within a few minutes. This image can be reproduced or enlarged later.

When color film is processed, the image in each layer consists of a colorant in a color complementary to the subject color: red gives a blue color, blue gives a yellow image, and green a magenta image (red base). The opposite happens when the positive is drawn: the blue-colored parts of the negative give magenta (red base) and yellow images on the paper, and their combination forms the red color, and so on.

In the case of reversible film for positive images, a black and white negative is first formed in the first appearance, then the unprinted parts are blocked out and finally the homogeneous color appearance of the positive images formed from the colors is revealed.

Color negative film:
The film records the colors of the subject in primary colors. The white color is printed on the three layers while the three primary colors (blue - green - red) are printed each color on its own layer.

- During processing, chemicals form complementary colorants for the negative: the red-sensitive layer forms a blue-blue image, the green a dark red image.

- The red filter is removed during processing.

- Colored paper acts like a negative film:
The dark red layer of the film is imprinted on the red-blue-sensitive layers of paper. After processing, the colorants are blue and the yellow (formed by color development) gives a green color by overlay.

The final negative is formed by overlaying three layers of colorants attached to the gelatin. The silver and silver salts are removed at the end of processing.

' Reversible film:

Reversible film records light and color just like negative film. The only real difference is the absence of the orange veil that gives the negative film its special appearance.

- The underlying image appears in black and white, which gives a negative image that forms colors. The undeveloped parts are then masked out.

- The film undergoes a monochromatic, homogeneous development similar to that of a color negative film, producing a positive image formed from the colorants. The silvery images formed during the two development processes are then removed by bleaching.

- Color Screen:
Most negative films are provided with an orange screen to improve the color quality of the final image. The fourth image below shows a scene of a negative screened after processing. This screen has been intentionally removed from all the other images to better illustrate the development stages.