What color is the white dress through the red filter?

Red is because of an opaque object, which is actually determined by the color light it reflects. Color filters are not color filters. They can be divided into red color filters, green color filters, purple color filters, blue color filters and yellow color filters, and each color filter can transmit its own color. They can be long wave pass type or band pass type. If it is a long wave type, in addition to its own color band, it can also pass a longer band than this band, even including near infrared wavelength. It can be divided into coated color filter and colored glass. An optical device for selecting a desired radiation band.

The common filter is that no filter can brighten the image of celestial bodies, because all filters will absorb certain wavelengths, thus darkening celestial bodies. This is a kind of flat glass or ordinary film with various colors, and its transmission bandwidth is hundreds of Egyptian meters. It is mainly used for broadband spectrophotometry or installed in a stellar spectrometer to isolate overlapping spectral levels. Its main feature is that its size can be made very large. The filter is made of plastic or glass sheets and special dyes. The red filter only allows red light to pass through, and so on.

The light transmittance of glass plate is similar to that of air, and all colored light can pass through, so it is transparent. But after dyeing with dyes, the molecular structure has changed, the refractive index has also changed, and the passage of some colored light has also changed. For example, if a beam of white light passes through a blue filter, it will emit a beam of blue light, with little green light and red light, and most of them will be absorbed by the filter. Filters are very useful and widely used in photography. Why are the main scenes of some landscape paintings taken by photographers always so prominent?

How did they do it? That's why filters are used. For example, if you want to shoot a yellow flower with a camera, the background is blue sky and green leaves. If you shoot as usual, the theme of the yellow flower can't stand out, because the image of the yellow flower is not prominent enough. However, if you put a yellow filter in front of the camera to block part of the green leaves and blue light in the blue sky and let a lot of yellow light pass through, then the yellow flower will be obvious and highlight the theme of the yellow flower.