تأثير التظهير على كثافة الفيلم وتباينه .. كتاب فن التصوير الفوتوغرافي

Effect of endorsement on film density and contrast

The image printed on the negative crystal has two important properties: intensity and contrast. These two characteristics are very important to make a good picture, so the photographer should understand them well.

Density is the intensity of the blackness of the image in general, the negative image and the printed image alike.
Contrast is the difference in intensity between places of light and places of shadow in the same image.
Suppose we photographed a white paper and a dark gray one on the same film, and this gives us the equivalent of high light (the white paper) and shadows (the gray paper). Let's start endorsing the film.

The high-light area (the white paper) begins to turn black, i.e. its density begins to increase; The blackness of this area increases more and more as the endorsement time increases, meaning that the density increases as the endorsement increases. This is the basic principle of endorsement.

What happens during this to the underexposed area represented by the gray paper?
This area will begin to appear after the high-light area has become quite dense. When this happens, the film will not only have density, but also contrast, because we define contrast as the difference between the intensity between the places of light and places of shadow on the same image. With the continuation of the endorsement, the density of the dark region increases at a faster rate than the increase in the density of the shadow region. As a result, the density difference between the two regions increases. You see, then, that the discrepancy increases with the increase in endorsement, and this is another basic principle of the endorsement principles.

Now let's take a picture of the same two papers, but by increasing the exposure ten times. In this case, we see that the two areas: the high light and the shade appear more quickly when endorsing compared to the same time in the previous case, that is, they become more intense for the same amount of time.
compared to the previous one.
Suppose that we appeared here during half the period compared to the previous case, and yet we get a density equal to or greater than that. The previous case is due to the increase in exposure in this case, but the short endorsement time will result in no significant difference in intensity between the light area and the shadow area, as was the case in the previous case, i.e. the difference in intensity will be less, and the contrast will be, therefore, less. , although the density, in the second case, is much higher than in the first case.

In order to verify this by printing the two negatives, we find that to get the same value of whiteness from the two negatives, the gray paper is lighter in the image resulting from the second negative, or what this means is that the contrast here between the light area and the shadow area is less, although if we look at the two negatives we see that the second Despite its lower contrast, it is more intense.

Remember the following and it helps you understand the general causes of density and contrast:
1- Endorsement affects density and contrast, but its first effect is on contrast.
2- The degree of exposure affects the intensity and contrast, but its first effect is on the intensity.