Black and white photography of filter

The use of filters in color photography was mainly discussed. Now let's see how to use filters in black and white photography. In black and white photography, the most important function of the filter is to highlight a certain gray tone to distinguish the colors represented by other gray tones. As we all know, all colors in black and white photos are reproduced with different shades of gray. When admiring the black and white photos of the Duchess, no one can tell whether the skirt she is wearing is red, blue or purple. Because all we see are gray tones. Sometimes, people don't pay special attention to the authenticity of colors, and they are very willing to accept black and white photos that don't reflect colors. However, black and white photos should also strive to be natural and true. Occasionally, we also want to highlight a certain color in a black-and-white photo to make it appear in sharp contrast. For example, what should I do if I want to highlight the bright red rose on the background of green leaves, the duchess's green dress on the background of blue velvet cloth, and reproduce various color patterns on textiles to make each color look different? In fact, all this can be done as long as you choose the right filter. So, what kind of filter is suitable? In order to understand this, we must understand a basic principle: the filter only allows light of the same color to pass through and blocks light of other colors. The yellow filter only lets yellow light pass through, but blocks other colors of light; The green filter only allows green light to pass through, but prevents light of other colors; The red filter only lets red pass, but blocks other colors of light, and so on. This principle has played a great role in black and white photography. Here, the red filter is taken as an example to explain this principle in detail. Because the red filter only lets the red light pass through, when shooting the red rose, the red light reflected by the red rose will pass through the filter unimpeded and be projected onto the film. On black and white film, what kind of results will this produce? A large number of river patterns reflected by red roses (most of the reflected light of red roses is red) are projected on black-and-white film, which will affect a large number of silver halide crystals in the corresponding areas on the film. When developing, all these crystals will become black metallic silver on the negative. Therefore, the negative left a picture of black and red roses. What will happen to this negative in the photo? We can imagine that the deeper part of the original negative will become a lighter gray image in the photo. We know that the red filter will block other colors except red light, so what will the green around the red rose look like in the photo? Because the red filter blocks the green light, only a small amount of green light can be projected onto the film. The less light is projected on the film, the less the silver halide crystal is affected. This means that the corresponding area of the negative film will be thinner after development and there will be less black metal silver. Therefore, the image of green leaves on the negative film is relatively shallow. So, what will the beautiful green leaves look like in the photo? We can also imagine that the brighter parts of the negative will appear deeper in the photo. Therefore, the green leaves in the photo will appear as dark gray images. Now, put the red flowers and green leaves together to see the overall effect. In the photo taken with the red filter, the red rose is in a lighter gray tone, and the green leaves are in a darker gray tone than the safflower. Results: The striking red roses were in sharp contrast with the green leaves.