نشأة مسحات الألوان ، وعلاجها في الصور الموجبة .. كتاب التصوير الملون

Genesis of color smears, and their treatment in positive images

How does Magenta Cast arise in colored positive images: Assuming that the density of the scarlet layer in the negative image is lower than that of the other two layers (yellow and cyan), what is the consequence of that when printing or enlarging on colored sensitive paper?

In response to the previous question, we say the following: The light source in the enlargement device or printing box emits white rays (consisting of red + green + blue) that travel on their way to permeate the colored negative, which consists of three colored layers (yellow + scarlet + cyan). ), and if the scarlet layer in the negative film is of low density, it will result in it not absorbing enough - the side of the white rays emitted by the light source, and this side is the green rays in this case, because the scarlet dye is responsible for absorbing the rays from
green. If the scouts of the scarlet dye increase, then the degree of absorption of the green rays will increase, and if the intensity of this dye decreases, then the absorption of these rays will decrease, and thus the percentage of green rays that permeate the negative image will exceed the percentage of the rest of the components of the white rays, which are the red and blue parts). It follows that the increase in the percentage of green rays that penetrate from the negative towards the sensitive colored paper increases its effect on the sensitive layer of the green rays (which bears the problems of the color magenta color formers), which is something that makes the positive image covered with a tinge of magenta cast. also .

1 The appropriate treatment in this case is to work to reduce the amount of green rays that led to an increase in the crimson color in the positive form, by placing a scarlet filter in front of the light source, because as we learned previously - it is the filter capable of absorbing the green rays.

Now that we know that the decrease in the density of the scarlet layer in the negative results in the emergence of a tinge of scarlet color on the positive, what is the appropriate treatment to remove this tinge in the following images?

Undoubtedly, we have deduced from the previous explanation the following fact:

If the colored positive image has a scarlet tinge, then the appropriate remedy to get rid of it in the next positive image is to place a scarlet filter in front of the light source (i.e. a filter of the same color as the tinge that affected the positive image and that we want to remove), and it must be The density of this filter is suitable for the intensity of the color hue, and unless a filter of the appropriate density is chosen, another defect will certainly arise, which we will talk about later on pg. 314 under the title “Over correction of cast”. Falak also appears clear in the colored paintings.
The emergence and treatment of yellow cast.

Worse than what we mentioned previously regarding the magenta cast, we find that the increase in the yellow tint in the positive form may be due to a decrease in the density of the first layer that carries the yellow dye in the negative form compared to the density of the other two layers, and thus the percentage of blue rays passing through the negative image increases. Its effect increases on the blue-sensitive layer of the positive photosensitive paper, which is the layer that carries yellow color formers, and thus the density of the silver image increases in this layer, and thus the density of the yellow dye image increases in it, and then we find the final positive image. It had a tinge of yellow to it.

In the same way as the aforementioned treatment (in the case of the scarlet smear), we find that to remove the yellow smear from the positive image, we must work to reduce the amount of blue rays that reach the sensitive paper, and that is by placing a yellow filter in the path of the rays.

That is, if the positive image is covered with a tinge of yellow, then we must place a yellow filter in the path of the rays emitted by the light source (i.e. a filter whose color is the same as the color of the smear to be removed), and its intensity must be equal to the intensity of the yellow tinge that hit the image. Positive, if we miscalculate the density of the filter, it is certain that the positive image will be affected by a tinge of another new color, which we will talk about later in Issue 314 under the title “Increasing this clearly in colored paintings.” Smear correction, it seems