تخفيض كثافة الصور السلبية.. كتاب التحميض والطبع والتكبير

Second: Reducing the density of negative images
REDUCTION PROCESS

As a result of overexposure or an increase in exposure time beyond the required limit, the negative image density increases. The details of the highly illuminated areas are less clear in the image of the subject that we photographed.

In order to avoid the previous defect, solutions that lead to a decrease in density are used. Reducers carry some salts that interact with silver and turn it into easily soluble salts. Thus, it is possible to get rid of the excess amount of silver.

Density reduction solutions differ from each other according to their effect on the degree of contrast. Some solutions increase contrast in addition to their effect in reducing density, while others reduce contrast in addition to reducing density. Accordingly, our choice of the appropriate solution depends on determining our desire to increase or decrease the degree of contrast, or in other words - on the actual defects that the negative image suffers from.

Chemical frills work with density reduction solutions:

It is possible to remove black spots, or any black parts in the negative, by means of density reduction solutions (Fig. 47) after washing the negative well and then immersing it in a basin of water containing several drops of wetting agents.

Reducing the density of images that suffer from a lack of contrast with an increase in density:
This defect usually results if the nursing increases too much with a lack of exposure, and then work should be done to reduce the intensity with a slight increase in contrast, and then it is repaired by one of the solutions known as Subtractive Reducers, whose effect increases in the low-density parts of the smear, which are the parts that represent the shadow areas in the original subject On its effect on the highly dense parts (which are the parts that represent the highly illuminated areas in the original subject). As a result of these characteristics, the degree of contrast increases slightly in addition to reducing the intensity of the image.

An example of this type of solution is the one known as Howard Farmer's Reducer, which was named after its author, and consists of an aqueous solution of potassium ferricyanide (toxic) and hypo. The matter is to silver ferrocyanide and the reaction takes place according to the following equation: - Silver + potassium ferrocyanide = silver ferrocyanide + potassium ferrocyanide.
And silver ferrocyanide dissolves in the hypo solution easily.

Reducing the density of the image that suffers from an increase in both intensity and contrast:

This defect is usually seen in the negatives that have increased the duration. And then it needs to reduce the density while reducing the degree of contrast. This is done by means of a solution called “Proportional Reducer”, and it was named as such due to its greater effect in areas in which a large amount of silver is deposited (which represents the highly luminous areas in the main subject) than in areas of shadows in which a lesser amount of silver is deposited. Transfer the degree of contrast at the same time while reducing the overall density of the image. The following are examples of the installation of this type of solutions.

Reducing the intensity of the image that suffers from an increase in its intensity with a significant increase in contrast:

In this case, it is necessary to reduce the degree of intensity while reducing the degree of contrast a lot. For this, solutions known as Super Proportional Reducers are used, which are not much different from the previous type, except that they have a stronger effect, as they reduce the intensity of the high-density areas, which are the high-light areas, in the original subject, to a degree that greatly exceeds their effect on the low-density areas, which are the shadows in the subject. This ultimately leads to a reduction in image density while reducing its contrast a lot at the same time.
The following is a statement for the installation of a solution of this type.